Why Are Some Plants Overcompensating?

Skyrocket_Gilia_(Ipomopsis_aggregata)_(9523007897).jpg

Gardeners are all too familiar with herbivory. Countless times I have been awaiting a bloom to burst only to have the buds nipped off the night before they opened. While this can be devastating for many plant species (not to mention my sanity), for certain plant species, an encounter with a hungry herbivore may actually lead to an increase in reproductive fitness.

Overcompensation theory is the idea that, under certain conditions, plants can respond to herbivore damage by producing more shoots, flowers, and seeds. It goes without saying that when this idea was originally proposed in the late 80's, it was met with its fair share of skepticism. Why would a plant capable of producing more shoots and flowers wait to be damaged to do so? The answer may lie in in the realm of biological trade-offs.

Overcompensation may evolve in lineages that tend to grow in habitats where there is a "predictable" amount of herbivory in any given growing season, perhaps a region where large herbivores migrate through annually. Plants in these habitats may conserve dormant growing tips and valuable resources to be used once herbivory has occurred. Perhaps this also serves as a cue to upregulate antiherbivory compounds in new tissues. The trade-off is that the plants incur a cost in the form of fewer flowers and thus reduced reproduction when herbivory is low or absent.

  Scarlet gilia ( Ipomopsis aggregata )

Scarlet gilia (Ipomopsis aggregata)

It could also be that plants are exhibiting two different strategies - one to deal with competition and one to deal with herbivory. If herbivory is low, plants may become more competitive, thus favoring rapid vertical growth of one or a couple shoots. When herbivory is high, rapid vertical growth becomes disadventageous and overcompensatory branching and flowering can provide the higher fitness benefits.

These possibilities are not mutually exclusive. In fact, since the late 80's, experts now believe that overcompensation is not an "either/or" phenomenon but rather a spectrum of possibilities that are dictated by the conditions in which the plants are growing. Certainly overcompensation exists but which conditions favor it and which do not?

Research on scarlet gilia (Ipomopsis aggregata), a biennial native to western North America, suggests that overcompensation comes into play only when environmental conditions are most favorable. Soil nutrients seem to play a role in how well a plant can bounce back following herbivore damage. When resources are high, the results can be quite astounding. Early work on this species showed that under proper conditions, plants that were browsed by upwards of 95% produced 2.4 times as much seed as uneaten control plants. What's more, the resulting seedlings were twice as likely to survive than their uneaten counterparts.

Things change for scarlet gilia growing in poor conditions. Low resource availability appears to place limits on how much any given plant may respond to browsing. Also, herbivory can really hamper flowering time. Because scarlet gilia is pollen limited, anything that can cause a disruption in pollinator visits can have serious consequences for seed set. In at least one study, browsed plants flowered later and received fewer pollinator visits as a result.

More recent work has been able to add more nuance to the overcompensation story. For instance, experiments done on two subspecies of field gentian (Gentianella campestris), add further support to the idea that overcompensation is a matter of trade-offs. They showed that, whereas competition with neighboring plants alone could not explain the benefits of overcompensation, browsing certainly can.

  Field gentian ( Gentianella campestris )

Field gentian (Gentianella campestris)

Plants growing in environments where herbivory was higher overcompensated by producing more branching, more flowers, and thus more seed, all despite soil nutrients. It appears that herbivory is the strongest predictor of overcompensation for this gentian. What's more, when these data were fed into population models, only the plants that responded to herbivory by overcompensation were predicted to show any sort of population growth in the long term.

Despite all of the interest overcompensation has recieved in the botanical literature, we are only just beginning to understand the biological mechanisms that make it possible. For starters, we know that when a dominant shoot or stem gets damaged or removed, it causes a reduction in the amount of the plant hormone auxin being produced. When auxin is removed, tiny auxiliary buds at the base of the plant are able to break dormancy and begin growing.

Removal of the dominant shoot or stem can also have major impact on the number of chromosomes present in regrowing tissues. Work on Arabidopsis thaliana revealed that when the apical meristem (main growing tip of a vertical stem) was removed, the plant underwent a process called "endoreduplication" in which the cells of the growing tissues actually duplicate their entire genome without undergoing mitosis.

Gentianaceae_-_Gentianella_campestris-6.JPG

Endoreduplication is a complex process with lots of biological significance but in plants it is often associated with stress responses. By duplicating the genomes of these new cells, the plants may be able to adjust more rapidly to their environment. This often manifests in changes to leaf size and shape and an uptick in plant defenses. Thus, plants may be able to fine tune the development of new tissues to overcompensate for browsing. Certainly far more work is needed to understand these mechanisms and their functions in more detail.

Overcompensation is not universal. Nonetheless, it is expected to occur in certain plants, especially those with short life cycles, and under certain environmental conditions, mainly when herbivore pressure and nutrient availability are relatively high. That being said, we still have plenty more to learn about this spectrum of strategies. When does it occur and when does it not? How common is it? What are the biological underpinnings of plants capable of overcompensation? Are some lineages more prone to overcompensation than others? Only more research can say for sure!

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4]

 

 

The Plight of the African Violets

b7c6396f1c0aa324200936f345c0194d.jpg

For many of us, African violets (Saintpaulia spp.) are some of the first houseplants we learned how to grow. They are not true violets (Violaceae), of course, but rather members of the family Gesneriaceae. Nonetheless, their compact rosettes of fuzzy leaves coupled with regular sprays of colorful flowers has made them a multi-million dollar staple of the horticultural industry. Unfortunately their numbers in captivity overshadow a bleak future for this genus in the wild. Many African violets are teetering on the brink of extinction.

The genus Saintpaulia is endemic to a small portion of east Africa, with a majority of species being found growing at various elevations throughout the Eastern Arc Mountains of Kenya and Tanzania. Most of the plants we grow at home are clones and hybrids of two species, S. ionantha and S. confusa. Collected in 1892, these two species were originally thought to be the same species, S. ionantha, until a prominent horticulturist noted that there are distinct differences in the seed capsules each produced. Since the 1890's, more species have been discovered.

  Saintpaulia goetzeana

Saintpaulia goetzeana

Exactly how many species comprise this genus is still up for some debate. Numbers range from as many as 20 to as few as 6. Much of the early work on describing various Saintpaulia species involved detailed descriptions of the density and direction of hairs on the leaves. More recent genetic work considers some of these early delineations to be tenuous at best, however, even these modern techniques have resolved surprisingly little when it comes to a species concept within this group.

  Saintpaulia  sp.  in situ .

Saintpaulia sp. in situ.

Though it can be risky to try and make generalizations about an entire genus, there are some commonalities when it comes to the habitats these plants prefer. Saintpaulia grow at a variety of elevations but most can be found growing on rocky outcrops. Most of them prefer growing in the shaded forest understory, hence they do so well in our (often) poorly lit homes. Their affinity for growing on rocks means that many species are most at home growing on rocks and cliffs near streams and waterfalls. The distribution of most Saintpaulia species is quite limited, with most only known from a small region of forest or even a single mountain. Its their limited geographic distribution that is cause for concern.

  Saintpaulia ionantha  subsp.  grotei in situ.

Saintpaulia ionantha subsp. grotei in situ.

Regardless of how many species there are, one fact is certain - many Saintpaulia risk extinction if nothing is done to save them. Again, populations of Saintpaulia species are often extremely isolated. Though more recent surveys have revealed that a handful of lowland species are more widespread than previously thought, mid to highland species are nonetheless quite restricted in their distribution. Habitat loss is the #1 threat facing Saintpaulia. Logging, both legal and illegal, and farming are causing the diverse tropical forests of eastern Africa to shrink more and more each year. As these forests disappear, so do Saintpaulia and all of the other organisms that call them home.

There is hope to be had though. The governments of Kenya and Tanzania have recognized that too much is being lost as their forests disappear. Stronger regulations on logging and farming have been put into place, however, enforcement continues to be an issue. Luckily for some Saintpaulia species, the type localities from which they were described are now located within protected areas. Protection coupled with inaccessibility may be exactly what some of these species need to survive. Also, thanks to the ease in which Saintpaulia are grown, ex situ conservation is proving to be a viable and valuable option for conserving at least some of the genetic legacy of this genus.

  Saintpaulia intermedia

Saintpaulia intermedia

It is so ironic to me that these plants can be so common in our homes and offices and yet so rare in the wild. Despite their popularity, few recognize the plight of this genus. My hope is that, in reading this, many of you will think about what you can do to protect the legacy of plants like these and so many others. Our planet and the species that call it home are doomed without habitat in which to live and reproduce. This is why land conservation is an absolute must. Consider donating to a land conservation organization today. Here are two worth your consideration:

The Nature Conservancy

The Rainforest Trust

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4] [5]

Is Love Vine Parasitizing Wasps?

6016714856_14eb405421_o.jpg

No, that's not dodder (Cuscuta sp.), its love vine (Cassytha filiformis), a member of the same family as the avacados in your kitchen (Lauraceae). It is a pantropical parasite that makes its living stealing water and nutrients from other plants. To do so, it punctures their vascular tissues with specialized structures called "haustoria." Amazingly, a recent observation made in Florida suggests that this botanical parasite may also be taking advantage of other parasites, specifically gall wasps.

Gall wasps are also plant parasites. They lay their eggs in developing plant tissues and the larvae release compounds that coax the plant to form nutrient-rich galls packed full of starchy goodness. Essentially you can think of galls as edible nursery chambers for the wasp larvae. While looking for galls on sand live oak (Quercus geminata) growing in southern Florida, Dr. Scott Egan and his colleagues noticed something odd. A small vine seemed to be attaching itself to the galls.

 Love vine draping a host plant. 

Love vine draping a host plant. 

The vine in question was none other than love vine and they were attached to galls growing on the underside of the oak leaves. What is strange is that, of all of the places that love vine likes to attach itself to its host (new stems, buds, petioles, and on the top and edge of leaves), the only time this vine showed any "interest" in the underside of oak leaves was when galls were present. Obviously this required further investigation.

The team discovered that at least two different species of gall wasps were being parasitized by love vine - one that produces small, spherical galls on the underside of oak leaves and one that forms large, multi-chambered galls on oak stems. Upon measuring the infected and uninfected galls, the team discovered that there were significant differences that could have real ecological significance.

 (A)  Cassytha filiformis  vine attaching haustoria to a leaf gall induced by the wasp  Belonocnema treatae  on the underside of their host plant,  Quercus geminata . (B) Labeled graphic of insect gall, parasitic vine, and vine haustoria. (C) Box plots of leaf gall diameter for unparasitized galls (control) and galls that have been parasitized by  C. filiformis . (D) Proportion of  B. treatae  leaf galls that contained a dead ‘mummified’ adult for unparasitized galls (control) and galls that have been parasitized by the vine  C. filiformis .  [SOURCE]

(A) Cassytha filiformis vine attaching haustoria to a leaf gall induced by the wasp Belonocnema treatae on the underside of their host plant, Quercus geminata. (B) Labeled graphic of insect gall, parasitic vine, and vine haustoria. (C) Box plots of leaf gall diameter for unparasitized galls (control) and galls that have been parasitized by C. filiformis. (D) Proportion of B. treatae leaf galls that contained a dead ‘mummified’ adult for unparasitized galls (control) and galls that have been parasitized by the vine C. filiformis. [SOURCE]

For the spherical gall wasp, infected galls tended to be much larger, however, the team feels that this may actually be due to the fact that the vine "prefers" larger galls. Astonishingly, larvae living in the infected galls were 45% less likely to survive. For the multi-chambered gall wasp, infection by love vine was associated with a 13.5% decrease in overall gall size. They suggest this is evidence that love vine is having net negative impacts on these parasitic wasps.

Subsequent investigation revealed that these wasps were not alone. In total, the team found love vine attacking the galls of at least two other wasps and one species of gall-making fly (though no data were reported for these cases). To be sure that love vine was in fact parasitizing these galls, they needed to have a closer look at what the vine was actually doing.

 Figure S2. (A)  Cassytha filiformis  vine attaching haustoria to a leaf gall induced by the wasp  Callirhytis quercusbatatoides  on the stem of their host plant,  Quercus geminata . (B) Labeled graphic of insect gall, parasitic vine, and vine haustoria on  C. quercusbatatoides . (C) Exemplar of parasitic vine wrapping tightly around the stem directly proximate to a gall induced by the wasp  Disholcaspis quercusvirens  on  Q. geminata . (D) Field site where love vine,  C. filiformis , is attacking the sand live oak,  Q. geminata , and many of the gall forming wasps on the same host plant.  [SOURCE]   

Figure S2. (A) Cassytha filiformis vine attaching haustoria to a leaf gall induced by the wasp Callirhytis quercusbatatoides on the stem of their host plant, Quercus geminata. (B) Labeled graphic of insect gall, parasitic vine, and vine haustoria on C. quercusbatatoides. (C) Exemplar of parasitic vine wrapping tightly around the stem directly proximate to a gall induced by the wasp Disholcaspis quercusvirens on Q. geminata. (D) Field site where love vine, C. filiformis, is attacking the sand live oak, Q. geminata, and many of the gall forming wasps on the same host plant. [SOURCE]
 

Dissection of the galls revealed that the haustoria were plugged into the gall itself, not the wasp larvae. However, because the larvae simply cannot develop without the nutrients and protection provided by the gall, Eagan and his colleagues conclude that these do indeed represent a case of a parasite being parasitized by another parasite.

At this point, the next question that must be asked is how common is this in love vine or, for that matter, across all other parasitic plants that utilize haustoria. Considering that parasites of parasites are nothing new in the biosphere, it is a safe bet that this will not be the last time this phenomenon is discovered.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1]

The Carnivorous Dewy Pine

19446001581_6e47ef8d27_o.jpg

The dewy pine is definitely not a pine, however, it is quite dewy. Known scientifically as Drosophyllum lusitanicum, this carnivore is odd in more ways than one. It is also growing more and more rare each year.

One of the strangest aspects of dewy pine ecology is its habitat preferences. Whereas most carnivorous plants enjoy growing in saturated soils or even floating in water, the dewy pine's preferred habitats dry up completely for a considerably portion of the year. Its entire distribution consists of scattered populations throughout the western Iberian Peninsula and northwest Morocco.

Drosophyllum_lusitanicum_Plantas_2011-5-22_SierraMadrona.jpg

Its ability to thrive in such xeric conditions is a bit of a conundrum. Plants stay green throughout the year and produce copious amounts of sticky mucilage as a means of catching prey. During the summer months, both air and soil temperatures can skyrocket to well over 100°F (37 °C). Though they possess a rather robust rooting system, dewy pines don't appear to produce much in the way of fine roots. Because of this, any ground water presence deeper in the soil is out of their reach. How then do these plants manage to function throughout the driest parts of the year?

During the hottest months, the only regular supply of water comes in the form of dew. Throughout the night and into early morning, temperatures cool enough for water to condense out of air. Dew covers anything with enough surface area to promote condensation. Thanks to all of those sticky glands on its leaves, the dewy pine possesses plenty of surface area for dew to collect. It is believed that, coupled with the rather porous cuticle of the surface of its leaves, the dewy pine is able to obtain water and reduce evapotranspiration enough to keep itself going throughout the hottest months. 

 Dewy pine leaves unfurl like fern fiddle heads as they grow.

Dewy pine leaves unfurl like fern fiddle heads as they grow.

As you have probably guessed at this point, those dewy leaves do more than photosynthesize and collect water. They also capture prey. Carnivory in this species evolved in response to the extremely poor conditions of their native soils. Nutrients and minerals are extremely low, thus selecting for species that can acquire these necessities via other means. Each dewy pine leaf is covered in two types of glands: stalked glands that produce sticky mucilage, and sessile glands that secrete digestive enzymes and absorb nutrients.

Their ability to capture insects far larger than one would expect is quite remarkable. The more an insect struggles, the more it becomes ensnared. The strength of the dewy pines mucilage likely stems from the fact that the leaves do not move like those of sundews (Drosera spp.). Once an insect is stuck, there is not much hope for its survival. Living in an environment as extreme as this, the dewy pine takes no chances.

Drosophyllum_lusitanicum_concurso_reserva_biosfera.jpg

The taxonomic affinity of the dewy pine has been a source of confusion as well. Because of its obvious similarity to the sundews, the dewy pine has long been considered a member of the family Droseraceae. However, although recent genetic work does suggest a distant relationship with Droseraceae and Nepenthaceae, experts now believe that the dewy pine is unique enough to warrant its own family. Thus, it is now the sole species of the family Drosophyllaceae.

Sadly, the dewy pine is losing ground fast. From industrialization and farming to fire suppression, dewy pines are running out of habitat. It is odd to think of a plant capable of living in such extreme conditions as being overly sensitive but that is the conundrum faced by more plants than just the dewy pine. Without regular levels of intermediate disturbance that clear the landscape of vegetation, plants like the dewy pine quickly get outcompeted by more aggressive plant species. Its the fact that dewy pine can live in such hostile environments that, historically, has kept its populations alive and well.

Drosophyllum_lusitanicum_Habitus_2011-4-21_SierraMadrona.jpg

What's more, it appears that dewy pines have trouble getting their seeds into new habitats. Low seed dispersal ability means populations can be cut off from suitable habitats that are only modest distances away. Without a helping hand, small, localized populations can disappear alarmingly fast. The good news is, conservationists are working hard on identifying what must be done to ensure the dewy pine is around for future generations to enjoy.

Changes in land use practices, prescribed fires, wild land conservation, and incentives for cattle farmers to adopt more traditional rather than industrial grazing practices may turn the table on dewy pine extinction. Additionally, dewy pines have become a sort of horticultural oddity over the last decade or so. As dedicated growers perfect germination and growing techniques, ex situ conservation can help maintain stocks of genetic material around the globe.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4]

 

 

Cycad Pollinators

8406039152_0380bd9ae3_o.jpg

When it comes to insect pollination, flowering plants get all of the attention. However, flowers aren't the only game in town. More and more we are beginning to appreciate the role insects play in the pollination of some gymnosperm lineages. For instance, did you know that many cycad species utilize insects as pollen vectors? The ways in which these charismatic gymnosperms entice insects is absolutely fascinating and well worth understanding in more detail.

Cycads or cycad-like plants were some of the earliest gymnosperm lineages to arise on this planet. They did so long before familiar insects like bees, wasps, and butterflies came onto the scene. It had long been assumed that, like a vast majority of extant gymnosperms, cycads relied on the wind to get pollen from male cones to female cones. Indeed, many species certainly utilize to wind to one degree or another. However, subsequent work on a few cycad genera revealed that wind might not cut it in most cases.

 White-haired cycad ( Encephalartos friderici-guilielm i)

White-haired cycad (Encephalartos friderici-guilielmi)

It took placing living cycads into wind tunnels to obtain the first evidence that something strange might be going on with cycad pollination. The small gaps on the female cones were simply too tight for wind-blown pollen to make it to the ovules. Around the same time, researchers began noting the production of volatile odors and heat in cycad cones, providing further incentives for closer examination.

Subsequent research into cycad pollination has really started to pay off. By excluding insects from the cones, researchers have been able to demonstrate that insects are an essential factor in the pollination of many cycad species. What's more, often these relationships appear to be rather species specific.

  Cycadophila yunnanensis ,  C. nigra , and other beetles on a cone of  Cycas  sp.

Cycadophila yunnanensis, C. nigra, and other beetles on a cone of Cycas sp.

By far, the bulk of cycad pollination services are being performed by beetles. This makes a lot of sense because, like cycads, beetles evolved long before bees or butterflies. Most of these belong to the superfamily Cucujoidea as well as the true weevils (Curculionidae). In some cases, beetles utilize cycad cones as places to mate and lay eggs. For instance, male and female cones of the South African cycad Encephalartos friderici-guilielmi were found to be quite attractive to at least two beetle genera. 

Beetles and their larvae were found on male cones only after they had opened and pollen was available. Researchers were even able to observe adult beetles emerging from pupae within the cones, suggesting that male cones of E. friderici-guilielmi function as brood sites. Adult beetles carrying pollen were seen leaving the male cones and visiting the female cones. The beetles would crawl all over the fuzzy outer surface of the female cones until they became receptive. At that point, the beetles wriggle inside and deposit pollen. Seed set was significantly lower when beetles were excluded.

 Male cone of  Zamia furfuracea  with a mating (lek) assembly of  Rhopalotria mollis  weevils.

Male cone of Zamia furfuracea with a mating (lek) assembly of Rhopalotria mollis weevils.

For the Mexican cycad Zamia furfuracea, weevils also utilize cones as brood sites, however, the female cones go to great lengths to protect themselves from failed reproductive efforts. The adult weevils are attracted to male cones by volatile odors where they pick up pollen. The female cones are thought to also emit similar odors, however, larvae are not able to develop within the female cones. Researchers attribute this to higher levels of toxins found in female cone tissues. This kills off the beetle larvae before they can do too much damage with their feeding. This way, the cycad gets pollinated and potentially harmful herbivores are eliminated. 

Beetles also share the cycad pollination spotlight with another surprising group of insects - thrips. Thrips belong to an ancient order of insects whose origin dates back to the Permian, some 298 million years ago. Because they are plant feeders, thrips are often considered pests. However, for Australian cycads in the genus Macrozamia, they are important pollinators.

  Macrozamia macleayi  female cone.

Macrozamia macleayi female cone.

Thrip pollination was studied in detail in at least two Macrozamia species, M. lucida and M. macleayi. It was noted that the male cones of these species are thermogenic, reaching peak temperatures of around   104 °F (40 °C). They also produce volatile compounds like monoterpenes as well as lots of CO2 and water vapor during this time. This spike in male cone activity also coincides with a mass exodus of thrips living within the cones.

 Thrips ( Cycadothrips chadwicki ) leaving a thermogenic pollen cone of  Macrozamia lucida.

Thrips (Cycadothrips chadwicki) leaving a thermogenic pollen cone of Macrozamia lucida.

Thrips apparently enjoy cool, dry, and dark places to feed and breed. That is why they love male Macrozamia cones. However, if the thrips were to remain in the male cones only, pollination wouldn't occur. This is where all of that male cone metabolic activity comes in handy. Researchers found that the combination of rising heat and humidity, and the production of monoterpenes aggravated thrips living within the male cones, causing them to leave the cones in search of another home.

Inevitably many of these pollen-covered thrips find themselves on female Macrozamia cones. They crawl inside and find things much more to their liking. It turns out that female Macrozamia cones do not produce heat or volatile compounds. In this way, Macrozamia are insuring pollen transfer between male and female plants.

 Thrips up close.

Thrips up close.

Pollination in cycads is a fascinating subject. It is a reminder that flowering plants aren't the only game in town and that insects have been providing such services for eons. Additionally, with cycads facing extinction threats on a global scale, understanding pollination is vital to preserving them into the future. Without reproduction, species will inevitably fail. Many cycads have yet to have their pollinators identified. Some cycad pollinators may even be extinct. Without boots on the ground, we may never know the full story. In truth, we have only begun to scratch the surface of cycads and their pollinators.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3] [4] [5] [6]

Fluorescent Bananas

4023036941_c9c93a3684_o.jpg

Bananas are one of the most popular fruits in the world. Love them or hate them, most of us know what they look like. Despite their global presence, few stop to think about where these fruits come from. That is a shame because bananas are fascinating plants for many reasons but now we can add blue fluorescence to that list.

Before we dive into the intriguing phenomenon of fluorescence in bananas, I think it is worth talking about the plants that produce them in a little more detail. Bananas belong to the genus Musa, which is located in its own family - Musaceae. Take a step back and look at a banana plant and it won't take long to realize they are distant relatives of the gingers. There are at least 68 recognized species of banana in the world and many more cultivated varieties. Despite their pan-tropical distribution, the genus Musa is native only to parts of the Indo-Malesian, Asian, and Australian tropics.

Starr_050826-4195_Musa_sp..jpg

Banana plants vary in height from species to species. At the smaller end of the spectrum you have species like the diminutive Musa velutina, which maxes out at about 2 meters (6 ft.) in height. On the taller side of things, there are species such as the monstrous Musa ingens, which can reach heights of 20 meters (66ft.)! Despite their arborescent appearance, bananas are not trees at all. They do not produce any wood. Instead, what looks like a tree trunk is actually the fused petioles of their leaves. Bananas are essentially giant herbs with the aforementioned M. ingens holding the world record for largest herb in the world.

When it comes time to flower, a long spike emerges from the main growing tip. This spike gradually elongates, revealing long, beautiful, tubular flowers arranged in whorls. For many banana species, bats are the main pollinators, however, a variety of insects will visit as well. In the wild, fruits appear following pollination, a trait that has been bred out of their cultivated relatives, which produce fruits without needing pollination. The fruits of a banana are actually a type a berry that dehisce like a capsule upon ripening, revealing delicious pulp chock full of hard seeds. Not all bananas turn yellow upon ripening. In fact, some are pink!

plant_banana_banana_shrub_green_food_banana_tree_leaf_bananas-1022525.jpg

For many fruits, the act of ripening often coincides with a change in color. This is a way for the plant to signal to seed dispersers that the fruits, and the seeds inside, are ready. As many of us know, many bananas start off green and gradually ripen to a bright yellow. This process involves a gradual breakdown of the chlorophyll within the banana skin. As the chlorophyll within the skin of a banana breaks down, it leaves behind a handful of byproducts. It turns out, some of these byproducts fluoresce blue under UV light. 

Amazingly, the fluorescent properties of bananas was only recently discovered. Researchers studying chlorophyll breakdown in the skins of various fruits identified some intriguing compounds in the skins of ripe Cavendish bananas. When viewed under UV light, these compounds gave off a luminescent blue hue. Further investigation revealed that as bananas ripen, their fluorescent properties grow more and more intense.

mfig001.jpg

There could be a couple reasons why this happens. First, it could simply be happenstance. Perhaps these fluorescent compounds are simply a curious byproduct of chlorophyll breakdown and serve no function for the plant whatsoever. However, bananas seem to be a special case. The way in which chlorophyll in the skin of a banana breaks down is quite different than the process of chlorophyll breakdown in other plants. What's more, the abundance of these compounds in the banana skin seems to suggest that the fluorescence does indeed have a function - seed dispersal.

Researchers now believe that the fluorescent properties of some ripe bananas serves as an additional signal to potential seed dispersers that the time is right for harvest. Many animals including birds and some mammals can see well into the UV spectrum and it is likely that the blue fluorescence of these bananas is a means of attracting such animals. Additionally, researchers also found that banana leaves fluoresce in a similar way, perhaps to sweeten the attractive display of the ripening fruits.

To date, little follow up has been done on fluorescence in bananas. It is likely that far more banana species exhibit this trait. Certainly more work is needed before we can say for sure what role, if any, these compounds play in the lives of wild bananas. Until then, this could be a fun trait to investigate in the comfort of your own home. Grab a black light and see if your bananas glow blue!

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2]

Light Pollution and Plants

I love walking around my town at night. Things really seem to slow down when the sun sets. Growing up in the country, my evening walks were lit only by the moon. Now that I live in civilization, however, street lights punctuate the darkness on every block. Walking around I can't help but wonder what all of this artificial light is doing to our photosynthetic neighbors. 

The vast majority of plants need light to make food. It doesn't matter if this light comes from the sun or a high powered electric light, as long as it is strong enough for photosynthesis. Even weaker wavelengths of light serve a purpose for our botanical friends. Plants can sense the relative length of uninterrupted darkness in their environment and they use that information for myriad internal processes. Its this dependence on light that makes many plant species vulnerable to our addiction to artificial lighting.

Just because a light isn't strong enough for photosynthesis doesn't mean it isn't affecting nearby plants. This is especially true for plants that use day length for timing events like bud break, flowering, and dormancy. The type of lighting favored by most municipalities emit wavelengths that peak especially high in the red to far-red ratio of the electromagnetic spectrum, which makes them particularly adept at disrupting plant photoperiods.

One of the most obvious effects of artificial lighting on plants can readily be seen in street trees growing in temperate regions. Though light sensitivity varies from species to species, trees growing near street lights tend to hold onto their leaves much longer in the fall than trees farther away. Because artificial lighting is enough to trick the red to far-red receptors in plants, it can "convince" trees that the days are longer than they actually are. Additional photosynthesis may not seem that bad but holding onto leaves longer makes trees more susceptible to ice damage. 

late fall.JPG

The effects of artificial lighting continues into spring as well. Trees growing near lights tend to break buds and flower earlier in the spring. This too makes them susceptible to frost damage. Early flowering plants run the risk of losing their entire reproductive effort by blooming before the threat of frost is gone. This can really mess up their relationship with pollinators. 

The effects of artificial lighting can even influence the way in which plants grow. Research has found that plants growing near street lights had larger leaves with more stomatal pores and these pores remained open for considerably longer than plants growing under unlit night conditions. This made them more susceptible to pollution and drought, two stressors that are all too common in urban environments. This issues is made much worse if the artificial lighting never turns off throughout the night. 

Artificial lighting affects more than just plant physiology too. Scaling up, the effects of night lights can have whole ecosystem consequences. For instance, researchers found that artificial lighting was enough to change the entire composition of grassland communities. Some plants responded well to artificial lights, producing more biomass and vegetative offshoots to the point that they pushed out other species. This was compounded by the change in reproductive output, with certain species showing higher seed production than others.

Effet_de_la_pollution_lumineuse_sur_l'arbre_urbain_Effect_of_light_pollution_on_urban_trees_and_dead_leaves_04.jpg

Changes in plant physiology, phenology, and composition also affect myriad other organisms in the environment. Changes in the timing of flowering or bud break can disrupt things like insects and birds that rely on these events for food and shelter. Research even suggests that forest regeneration is being altered by artificial lighting. Seed dispersers such as bats often will not fly into well-lit areas at night, therefore reducing the amount of seeds falling in those areas. Such research is still in its infancy meaning we have a lot more to learn about how artificial lighting is disrupting natural events.

Light pollution is so much more than an aesthetic issue. Artificial lighting is clearly having pronounced effects on plant life. Disrupt plants and you disrupt life as we know it. Certainly more work is needed to tease out all the ways in which lights influence plants, however, it is clear that we must work hard on reducing light pollution around the globe.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]

Fossils Shine Light On the History of Gall-Making Wasps

Common_spangle_galls_-_geograph.org.uk_-_568302.jpg

We can learn a lot about life on Earth from the fossil record. I am always amazed by the degree of scrutiny involved in collecting data from these preserved remains. Take, for instance, the case of gall-making wasp fossils found in western North America. A small collection of fossilized oak leaves is giving researchers insights into the evolutionary history of oaks and the gall-making wasps they host.

Oaks interact with a bewildering array of insects. Many of these are gall-making wasps in the family Cynipidae. Dozens of different wasp species can be found on a single oak tree. Female wasps lay their eggs inside developing oak tissues and the larvae release hormones and other chemicals that cause galls to form. Galls are essentially edible nursery chambers. Other than their bizarre shapes and colors, the compounds released by the wasp larvae reduce the chemical defenses of the oak and increase the relative nutrition of the tissues themselves. Often, these relationships are precise, with specific wasp species preferring specific oak species. But when did these relationships arise? Why are oaks so popular? What can fossil evidence tell us about this incredible relationship?

Cynips_sp_beentree.jpg

Though scant, the little fossil evidence of oak galls can tell us a lot. For starters, we know that gall-making wasps whose larvae produce structures similar to that of the Cynipids have been around since at least the late Cretaceous, some 100 million years ago. However, it is hard to say for sure exactly who made these galls and exactly what taxonomic affinity the host plant belongs to. More conclusive Cynipid gall fossils appear again in the Eocene and continue to pop up in the fossil record throughout the Oligocene and well into the Miocene (33 - 23 million years ago).

Miocene aged fossils are where things get a little bit more conclusive. Fossil beds located in the western United States have turned up fossilized oak leaves complete with Cynipid galls. The similarity of these galls to those of some present day species is incredible. It demonstrates that these relationships arose early on and have continued to diversify ever since. What's more, thanks to the degree of preservation in these fossil beds, researchers are able to make some greater conclusions about why gall-making wasps and oaks seem to be so intertwined.

 Holotype of Antronoides cyanomontanus galls on fossilized leaves of  Quercus simulata . 1) Impression of the abaxial surface of the leaf, showing the galls extending into the matrix. 2) Galls showing close association with secondary veins. 3) Gall showing the impression of rim-like base partially straddling the secondary vein. 4) Close-up of gall attached at margin extending down into the matrix. 5) Gall uncovered revealing spindle-shaped morphology.

Holotype of Antronoides cyanomontanus galls on fossilized leaves of Quercus simulata. 1) Impression of the abaxial surface of the leaf, showing the galls extending into the matrix. 2) Galls showing close association with secondary veins. 3) Gall showing the impression of rim-like base partially straddling the secondary vein. 4) Close-up of gall attached at margin extending down into the matrix. 5) Gall uncovered revealing spindle-shaped morphology.

 1)  Xanthoteras clavuloides  galls on fossilized  Quercus lobata , showing gall attached to secondary vein. Specimen in California Academy of Sciences Entomology collection, San Francisco. 2) Two galls of attached to a secondary vein showing overlap of their bases. Specimen in California Academy of Sciences Entomology Collection, San Francisco. 3) Three galls collected from leaf of California  Quercus lobata  showing clavate shape and expanded, ring-like base. 4) Gall showing the annulate or ribbed aspect of the base, which is similar to bases of  Antronoides cyanomontanus  and  A. polygonalis . 5) Galls showing clavate shape, pilose and nonpilose surfaces, and bases.

1) Xanthoteras clavuloides galls on fossilized Quercus lobata, showing gall attached to secondary vein. Specimen in California Academy of Sciences Entomology collection, San Francisco. 2) Two galls of attached to a secondary vein showing overlap of their bases. Specimen in California Academy of Sciences Entomology Collection, San Francisco. 3) Three galls collected from leaf of California Quercus lobata showing clavate shape and expanded, ring-like base. 4) Gall showing the annulate or ribbed aspect of the base, which is similar to bases of Antronoides cyanomontanus and A. polygonalis. 5) Galls showing clavate shape, pilose and nonpilose surfaces, and bases.

Gall-making wasps seem to diversify at a much faster rate in xeric climates. The fossil records during this time show that mesic tree speciess were gradually being replaced by more xeric species like oaks. Wasps seem to prefer these drier environments and the thought is that such preferences have to do with disease and parasite loads.

Again, galls a large collections of nutrient-rich tissues that are low in defense compounds. Coupled with the juicy grub at their center, it stands to reason that galls make excellent sites of infection for fungi and other parasites. By living in drier habitats, it is believed that gall-making wasps are able to escape these environmental pressures that would otherwise plague them in wetter habitats. The fossil evidence appears to support this hypothesis and today we see similar patterns. White oaks are especially drought tolerant and its this group of oaks that host the highest diversity of gall-making wasps.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

Meet the Blazing Stars

Liatris_aspera3.jpg

Midsummer in North America is, among other things, Liatris season. These gorgeous plants are often referred to as blazing stars or gayfeathers, which hints at the impact their flowers have on our psyche. Whether in the garden or in the wild, Liatris are a group of plants worth getting to know a bit better.

Liatris is by and large a North American genus with only a single species occurring in the Bahamas. Though we often think of Liatris as prairie plants, the center of diversity for this group is in the southeastern United States. Taxonomically speaking, Liatris are a bit of a conundrum. Something like 40 different species have been described and, where ranges overlap, many putative hybrids have been named.

 Rocky Mountain blazing star ( Liatris ligulistylis )

Rocky Mountain blazing star (Liatris ligulistylis)

Authorities on this group cite ample confusion when it comes to drawing lines between species. Much of this confusion comes from the fact that numerous variants and intergradations exist between the various species. As mentioned, hybridization is not uncommon in this genus, which complicates matters quite a bit.

 Prairie blazing star ( Liatris pycnostachya )

Prairie blazing star (Liatris pycnostachya)

Liatris as a whole appears to have undergone quite an adaptive radiation in North America, with species adapting to specific soils and habitat types. Take, for instance, the case of cylindrical blazing star (L. cylindracea), marsh blazing star (L. spicata), and rough blazing star (L. aspera). The ranges of these species overlap to quite a degree, however, each prefers to grow in soils of specific texture and moisture. Marsh blazing star, as you may have guessed, prefers wetter soils whereas rough blazing star enjoys drier habitats. Cylindrical blazing star seems to enjoy intermediate soil conditions, especially where soil pH is a bit higher. As such, these three species often occur in completely different habitats. However, in places like the southern shores of Lake Michigan, they find themselves growing in close quarters and as a result, a fair amount of hybridization has occurred.

 Rough blazing star ( Liatris aspera )

Rough blazing star (Liatris aspera)

Another example of confusion comes from a species commonly known as the savanna blazing star (Liatris scariosa nieuwlandii). Many different ecotypes of this plant exist and some experts don't quite know how to deal with them all. Sometimes savanna blazing star is treated as a variant of another species called the northern blazing star (Liatris scariosa var. nieuwlandii) and sometimes it is treated as its own distinct species (Liatris nieuwlandii). Until proper genetic work can be done, it is impossible to say which, if any, are correct. 

 Glandular blazing star ( Liatris glandulosa )

Glandular blazing star (Liatris glandulosa)

Taxonomic confusion aside, the various Liatris species and variants are important components of the ecology wherever they occur. Numerous insects feed upon and raise their young on the foliage and few could argue against their flowers as pollinator magnets. All Liatris produce pink to purple flowers in splendid Asteraceae fashion. Every once in a while, an aberrant form is produced that sports white flowers. Though horticulturists have capitalized on this for the garden, at least one authority claims that these white forms are much weaker than their pink flowering parents. At least one species, the pinkscale blazing star (L. elegans), produces large, filamentous white bracts that very much resemble flowers.

 Check out the bracts on the pinkscale blazing star ( L. elegans )!

Check out the bracts on the pinkscale blazing star (L. elegans)!

Liatris are just as interesting below as they are above. The roots, foliage, and flowers all emerge from a swollen underground stem called a corm. The formation of these corms is one reason why some Liatris species have become so popular in our gardens. It makes them extremely hardy during the dormant season. In the spring, the corm starts forming roots. At the same time, tiny preformed buds at the top of the corm begin to grow this years crop of leaves and flowers. By the end of the growing season, the corm has reached its maximum size for that year and the plant draws down the rest of its reserves to wait out the winter.

 Cylindrical blazing star ( Liatris cylindracea )

Cylindrical blazing star (Liatris cylindracea)

During this time, some species form a layer of tissue along the edge of the corm that is much darker in coloration than what was laid down earlier in the season. This has led some to suggest that aging individual Liatris is possible. Experts believe that specimens can readily reach 30 to 40 years of age or more, however, the degree to which these dark bands indicate annual growth is up for a lot of debate. Others have found no correlation with plant age. Regardless, it is safe to say that many Liatris species can live for decades if left undisturbed.

 Scrub blazing star ( Liatris ohlingerae )

Scrub blazing star (Liatris ohlingerae)

All in all, Liatris is a very special, albeit slightly confusing, group of plants. It offers a little something for everyone. What's more, their beauty is only part of the story. These are ecologically important plants that support many great insect species. As summer wears on, make sure to get out there and enjoy the Liatris in your neck of the woods. You will be happy you did!

Photo Credits: [1] [2] [3] [4] [5] [6] [7] [8]

Further Reading: [1] [2] [3]

 

 

 

Giant Hogweed And Other Toxic Plants

Heracleum_mantegazzianum_(Meise)_JPG1b.jpg

Everybody run, giant hogweed is coming! I am sure by now, many of you reading this will have picked up a story or two about a nasty invasive plant that will render you blind and nursing third degree burns. Indeed, giant hogweed (Heracleum mantegazzianum) is a plant worth learning how to identify. However, the tone of these articles is often one of hysterics, leaving the reader feeling like this plant is more like a Triffid, actively uprooting itself to hunt down unwary humans. Is giant hogweed worth all of this anxiety?

runaway.gif

Let's start with the plant itself. Giant hogweed is a member of the carrot family (Apiaceae). Its native range encompasses much of the Caucasus region and into parts of central Asia. It was (and probably still is in some areas) considered a wonderfully large and unique addition to a temperate garden. And large it is. Individual plants regularly reach heights of 6 feet (2 m) or more and some records indicate that individuals over 10 feet (3 m) in height are not unheard of.

Heracleum_mantegazzianum_(Meise)_JPG1a.jpg

Because it was once a popular garden plant, this species has been introduced far outside of its native range. For many decades, giant hogweed probably lurked in the background unnoticed, its seeds finding favorable spots for germination among other weedy plants along roadsides, fallow fields, and abandoned lots. In the last few years it has grown harder to ignore. More and more plants are showing up where they shouldn't. Indeed, it seems that giant hogweed is yet another invasive species we need to get on top of. But what about all of that panic? Certainly its invasive status alone isn't what all the hype is about.

Well, like all members of the carrot family, giant hogweed produces an impressive array of chemical compounds. Many of these compounds serve to protect the plants from hungry herbivores and a plethora of microbial infections. Some of the compounds in the giant hogweed arsenal are a group known as the furocoumarins. These compounds defend the plant in a rather alarming way. These furocoumarins are phototoxic, which means when the sap gets on the body of an animal and is exposed to sunlight, they cause severe chemical burns.

 Giant hogweed when not in bloom.

Giant hogweed when not in bloom.

Stories of people being hospitalized due to an unfortunate run in with this plant make headlines wherever it pops up. That being said, simply touching the plant isn't going to hurt you. The chemicals are sloshing around in the sap of giant hogweed and the plant needs to be injured in some way before they will leak out onto whatever is hurting it. For humans, this usually occurs while mowing or weed whacking, or if a child mistakenly uses the hollow stem as a pea shooter.

With stories like this floating around, it is no wonder then why people get so upset when this plant shows up. However, I can't help but feel that this is being fed on a bit by media fear-mongering. It is worth putting giant hogweed into some practical context. It may actually alarm you to know just how many plants on the landscape have the ability to cause you harm if handled the wrong way.

 Wild parsnip ( Pastinaca sativa )

Wild parsnip (Pastinaca sativa)

Even hogweeds less robust relatives are capable of causing phototoxic reactions. I once weed whacked a large patch of Queen Anne's lace (Daucus carota) and wild parsnip (Pastinaca sativa) and ended up covered in nasty blisters the next day. I recovered but I sure did learn to give those two species more respect whenever I encountered them. Plants like poison ivy, oak, and sumac certainly cause their fair share of misery but even these do not get the sort of media attention that giant hogweed does.

Even more interesting are some of the species we actively plant in our gardens. For instance, castor bean (Ricinus communis) is quite popular among gardeners and it is responsible for producing ricin, a protein with enough killing power to bring down an adult human many times over. Take a bite out of the castor bean in your garden and it will be the last thing you ever eat. Even more potent than ricin is aconitine, an alkaloid produced by beloved garden plants like the monkshoods (Aconitum) and the larkspurs (Delphinium). This powerful alkaloid causes your nervous system to endlessly fire, leading to convulsions and death.

 Castor bean ( Ricinus communis )

Castor bean (Ricinus communis)

Similarly, a few different species of Datura are commonly grown around the world. Datura posioning is nothing to mess with and symptoms include "a complete inability to differentiate reality from fantasy; hyperthermia; tachycardia; bizarre, and possibly violent behavior; and severe mydriasis (dilated pupils) with resultant painful photophobia that can last several days." Even plants we grow for food can hurt us in bad ways. Most members of the tomato family produce a multitude of toxic alkaloids like solanine. That is why only ripe tomatoes and eggplants should ever be consumed.

 Jimsonweed ( Datura stramonium )

Jimsonweed (Datura stramonium)

In reality, I could devote an entire blog and podcast series to the chemical warfare plants have taken up during their long and complicated evolutionary history. Long story short, plants are sessile organisms that must defend themselves in order to survive and toxic chemicals are really great means to do just that. The reality is that we welcome many toxic and potentially harmful plants (both knowingly and unknowingly) into our lives and it seems slightly odd that species like giant hogweed warrant such fervor from media outlets. That being said, it is important to treat these plants with the respect they deserve. Don't bother them and they won't bother you.

So, is giant hogweed coming to attack you and your family? No. Is giant hogweed a plant worth learning to identify? Yes. Is giant hogweed dangerous to humans? Yes, but only under certain conditions.

Plants like giant hogweed are the perfect reminder as to why we must give plants more respect in our society. Teaching friends and family which plants can feed them and which plants can hurt them is something everyone should invest some time in doing. If you find giant hogweed in your area and you do not live in the Caucasus or central Asia, don't be a hero. Call a professional to come and deal with it. Otherwise, stay calm and keep on botanizing. Giant hogweed is not out to get you.

Photo Credits: [1] [2] [3] [4] [5] [6] [7]

Further Reading: [1] [2] [3]

Life With Endophytic Fungi

 Endophytic fungi living in the cells of a grass leaf.

Endophytic fungi living in the cells of a grass leaf.

Talk about plants long enough and fungi eventually make their way into the conversation. These two walks of life are inextricably linked and probably have been since the earliest days. At this point we are well aware of beneficial fungal partners like mycorrhizae or pathogens like the cedar apple rust. Another type of relationship we are only starting to fully appreciate is that of plants and endophytic fungi living in their above ground tissues. 

Endophytic fungi have been discovered in many different types of plants, however, it is best studied in grasses. The closer we look at these symbiotic relationships, the more complex the picture becomes. There are many ways in which plants can benefit from the presence of these fungi in their tissues and it appears that some plants even stock their seeds with fungi, which appears to give their offspring a better chance at establishment. 

To start, the benefits to the fungi are rather straight forward. They get a relatively safe place to live within the tissues of a plant. They also gain access to all of the carbohydrates the plants produce via photosynthesis. This is not unlike what we see with mycorrhizae. But what about the plants? What could they gain from letting fungi live in and around their cells?

One amazing benefit endophytic fungi offer plants is protection. Fungi are famous for the chemical cocktails they produce and many of these can harm animals. Such benefits vary from plant to plant and fungi to fungi, however, the overall effect is largely the same. Herbivores feeding on plants like grasses that have been infected with endophytic fungi are deterred from doing so either because the fungi make the plant distasteful or downright toxic. It isn't just big herbivores that are deterred either. Evidence has shown that insects are also affected.

There is even some evidence to suggest that these anti-herbivore compounds might have influences farther up the food chain. It usually takes a lot of toxins to bring down a large herbivore, however, some of these toxins have the potential to build up in the tissues of some herbivores and therefore may influence their appeal to predators. Some have hypothesized that the endophytic fungal toxins may make herbivores more susceptible to predators. Perhaps the toxins make the herbivores less cautious or slow them down, making them more likely targets. Certainly more work is needed before anyone can say for sure.

 Italian ryegrass ( Lolium multiflorum ) is one of the most studied grasses that host endophytic fungi.

Italian ryegrass (Lolium multiflorum) is one of the most studied grasses that host endophytic fungi.

Another amazing example deals with parasitoids like wasps that lay their eggs in other insects. Researchers found that female parasitoid wasps can discriminate between aphids that have been feeding on plants with endophytic fungi and those without endophytic fungi. Wasp larvae developed more slowly and had a shorter lifespan when raised in aphids that have fed on endophytic fungi plants. As such, the distribution of plants with endophytic symbionts may have serious ramifications for parasitoid abundance in any given habitat.

Another benefit these endophytic fungi offer plants is increased photosynthesis. Amazingly, some grasses appear to photosynthesize better with endophytic fungi living in their tissues than plants without fungi. There are many mechanisms by which this may work but to simplify the matter, it appears that by producing defense compounds, endophytic fungi allow the plant to redistribute their metabolic processes towards photosynthesis and growth. In return, the plants produce more carbohydrates that then feed the fungi living in their tissues. 

One of the most remarkable aspects about the relationship between endophytic fungi and plants is that the plants can pass these fungi on to their offspring. Fungi are able to infect the tissues of the host plants' seeds and therefore can be carried with the seeds wherever they go. As the seedlings grow, so do the fungi. Some evidence suggests this gives infected seedlings a leg up on the competition. Other studies have not found such pronounced effects.

Still other studies have shown that it may not be fungi in the seeds that make a big difference but rather the fungi present in the decaying tissues of plants growing around them. Endophytic fungi have been shown to produce allelopathic compounds that poison neighboring plants. Areas receiving lots of plant litter containing endophytic fungi produced fewer plants but these plants grew larger than areas without endophytic fungi litter. Perhaps this reduces competition in favor of plant species than can host said endophytes. Again, this has potentially huge ramifications for the diversity and abundance of plant species living in a given area.

We are only beginning to understand the role of endophytic fungi in the lives of plants and the communities they make up. To date, it would appear that endophytic fungi are potentially having huge impacts on ecosystems around the globe. It goes without saying that more research is needed.

Photo Credits: [1] [2]

Further Reading: [1] [2] [3] [4] [5] [6]

                                                        

Growing Camouflage

 A garden on the back of a weevil living a humid Chilean rainforest.

A garden on the back of a weevil living a humid Chilean rainforest.

Lots of us will be familiar with organisms like decorator crabs that utilize bits and pieces of their environment, especially living sea anemones, as a form of camouflage and protection. Examples of terrestrial insects attaching bits and pieces of lichens to their body are not unheard of either. However, there are at least two groups of arthropods that take their camouflage to a whole new level by actively growing miniature gardens on their bodies.

Little is known about these garden-growing arthropods. To date, these miniature gardens have only been reported on a few species of weevil in the genus Gymnopholus as well as a species of millipede called Psammodesmus bryophorus. Coined epizoic symbiosis, it is thought that these gardens serve as a form of protection by camouflaging the gardeners against the backdrop of their environment.

 Bryophytes on a  Psammodesmus bryophorus  male.

Bryophytes on a Psammodesmus bryophorus male.

Indeed, both groups of arthropods frequent exposed areas. What is most remarkable about this relationship is that these plants were not placed on the carapace from elsewhere in the environment. Instead, they have been actively growing there from the beginning. Closer inspection of the cuticle of these arthropods reveals unique structural adaptations like pits and hairs that provide favorable microclimates for spores to germinate and grow.

The plant communities largely consist of mosses and liverworts. At least 5 different liverwort families are represented and at least one family of moss. Even more remarkable is the fact that even these small botanical communities are enough to support a miniature ecosystem of their own. Researchers have found numerous algae such as diatoms, lichens, and a variety of fungi growing amidst the mosses and liverworts. These in turn support small communities of mites. It appears that an entire unknown ecosystem lives on the backs of these mysterious arthropods.

 FIGURE 39. Elytral base of Gymnopholus (Niphetoscapha) nitidus with exudates. FIGURES 40a–b. Gymnopholus (Niphetoscapha) inexspectatus sp. n., live specimen with incrustrations of algae and lichens; photographs M. Wild, Mokndoma.  [SOURCE]

FIGURE 39. Elytral base of Gymnopholus (Niphetoscapha) nitidus with exudates. FIGURES 40a–b. Gymnopholus (Niphetoscapha) inexspectatus sp. n., live specimen with incrustrations of algae and lichens; photographs M. Wild, Mokndoma. [SOURCE]

There is still much to be learned about this symbiotic relationship. Although camouflage is the leading hypothesis, no work has been done to actually investigate the benefits these arthropods receive from actively growing these miniature gardens on their backs. Mysteries still abound. For instance, in the case of the millipede, gardens are found more frequently on the backs of males than on the backs of females. Could it be that males spend more time searching their environment and thus benefit from the added camouflage? Only further research will tell.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]

Meet the Crypts

26165576_2033477836679071_8698732942376159621_n.jpg

If you have ever spent time in an aquarium store, you have undoubtedly come across a Cryptocoryne or two. Indeed, these plants are most famous for their indispensable role in aquascaping freshwater aquaria. As organisms, however, crypts receive considerably less attention. Nonetheless, a handful of dedicated botanists have devoted time and effort to understanding this wonderful genus of tropical Aroids. What follows is a brief introduction to the world of Cryptocoryne plants. 

Cryptocoryne is a genus that currently consists of around 60 - 65 species, all of which are native to tropical regions of Asia and New Guinea. Every few years it seems at least one or two new species are added to this list and without a doubt, more species await discovery. All crypts are considered aquatic to one degree or another. Ecologically speaking, however, species fall into four broad categories based on the types of habitats they prefer.

  Cryptocoryne cognata in situ .

Cryptocoryne cognata in situ.

The most familiar crypts grow along the banks of slow-moving rivers and streams and find themselves submerged for a large portion of their life. Others grow in seasonally flooded habitats and experience a pronounced dry season. These species usually go dormant until flood waters return. Still others can be found growing in swampy forested habitats, often in acidic peat swamps. Finally, a few crypts have adapted to living in tidal zones in both fresh and brackish waters.

Like all aquatic plants, crypts face a lot of challenges living in water. One of the biggest challenges is reproduction. Despite their aquatic nature, crypts will not flower successfully underwater. If growing submerged, most crypt species reproduce vegetatively via a creeping rhizome. As such, crypts often form large, clonal colonies in both the wild and in aquaria, a fact that has made a few crypts aggressive invaders in places like Florida.

  Cryptocoryne wendtii  is one of the most common species in the aquarium trade. Its textured leaves are thought to have a higher surface area, allowing this plant to thrive in shaded aquatic habitats.

Cryptocoryne wendtii is one of the most common species in the aquarium trade. Its textured leaves are thought to have a higher surface area, allowing this plant to thrive in shaded aquatic habitats.

Given proper hydrologic cycles, however, crypts will flower and when they do, it is truly a sight to behold. As is typical of aroids, crypts produce an inflorescence comprised of a spadix with whirls of male and female flowers covered by a decorative sheath called a spathe. This spathe is the key to successful flowering among the various crypt species.

 Species like  C. becketti  have become invasive in places like Florida, no doubt thanks to aquarium hobbyists.

Species like C. becketti have become invasive in places like Florida, no doubt thanks to aquarium hobbyists.

If the spathe were to open underwater, the inflorescence would quickly rot. Instead, most crypts seem to have an uncanny ability to sense water levels. At early stages of development, the spathe completely encloses the developing spadix in a water tight package. The tubular spathe continues to grow upward until the top has breached the surface. Consequently, the overall length of a crypt inflorescence is highly variable depending on the water level of its habitat. Crypts living in tidal zones take this a step further. Somehow they are able to time their flowering events to the ebb and flow of the tides, only producing flowers during periods of the month when tides are at their lowest.

  Cryptocoryne ligua

Cryptocoryne ligua

With the tip of the inflorescence safely above water, the spathe will finally open revealing their surprisingly complex anatomy and coloration. It is a shame that most crypt growers never get to see such floral splendor in person. The spathe of many crypt species emit a faint but unpleasant odor. Additionally, some species adorn the spathe with fringes that, coupled with stark coloration, is thought to improve the chances of pollinator visitation.

Pollinators are poorly studied among crypts, however, it is thought that small flies take up the bulk of the work. Lured in by the promise of a rotting meal on which they can feed and lay their eggs, the flies become trapped inside the long tube of the spathe. Like the pitfall traps of a pitcher plant, the inner walls of the spathe are coated in a waxy substance that keeps the insects from crawling out before they do their job.

In general, the female flowers mature first. If the insect inside has visited a crypt of the same species the day before, it is likely carrying pollen and thus deposits said pollen onto the stigmas of the current crypt. After the female flowers have had a chance at being fertilized, the male flowers then mature. The insects inside are then dusted with new pollen, the walls of the spathe lose their slippery properties, and the insects are released in hopes of repeated the process again.

 The fruit of a  Cryptocoryne  is called a syncarp.

The fruit of a Cryptocoryne is called a syncarp.

To the best of my knowledge, most crypts are not self-compatible. Instead, plants must receive pollen from unrelated individuals to set seed. Because large crypt colonies are often made up of clones of a single mother plant, sexual reproduction can be rather infrequent among the various species. Nonetheless sexual reproduction does occur and the seeds are produced in a different way than most other aroids. Instead of berries, crypts produce their seeds in a aggregated collection of fruits called a syncarp. When ripe, the syncarp opens like a little star and the seeds float away on the current.

One species, Cryptocoryne ciliata, takes seed production to a whole different level by producing viviparous seeds. Before the syncarp even opens, the seeds actually germinate on the mother plant. In this way, tiny seedlings complete with roots and leaves are released instead of seeds. Seedlings have a much greater surface area than seeds and readily get stuck in mud as well as other aquatic vegetation. In this way, C. ciliata offspring get a jump start on the establishment process. It is no wonder then that C. ciliata has one of the widest distributions of any of the crypt species.

  Cryptocoryne ciliata

Cryptocoryne ciliata

Despite plenty of overlap among the ranges of various crypt species, the genus displays an amazing array of variation. Some have likened crypts to Araceae's version of Darwin's finches in that the unique ecology of each species appears to have created barriers to species introgression. Though hybrids do occur, each crypt seems to maintain its own niche via a unique habitat requirement, differing flower phenology, or a specific set of pollinators. It would appear that much can be learned about the mechanics of speciation by studying the various Cryptocoryne and their habits.

Unfortunately, the limited geographic distribution and specific habitat requirements of crypt species is cause for concern. Many are growing more and more rare as human settlements expand and destroy valuable crypt habitat. As popular as some crypts may be in cultivation, many others have proven too idiosyncratic to grow on a commercial level. More work is certainly needed to properly assess populations and bring plants into cultivation as a form of ex situ conservation.

  Cryptocoryne cordata  Var. Siamensis 'Rosanervig' is a contoversial variety names recognized by the stark patterns of venation on its leaves.

Cryptocoryne cordata Var. Siamensis 'Rosanervig' is a contoversial variety names recognized by the stark patterns of venation on its leaves.

Proper study is further complicated by the fact that many crypt species are highly plastic. They have to be in order to survive the rigors of their aquatic environment. True species identification can really only be assessed when flowers are present and some populations seem to prefer vegetative over sexual reproduction a majority of the time. A multitude of subspecies exist, though the degree to which they should be formally recognized is up for debate.

I think it is safe to say that Cryptocoryne is a genus worth far more attention than it currently receives. They are without a doubt important components of the ecology of their native habitats and humans would do well to understand them a bit better. With a bit more attention from botanical gardens and other conservation organizations, perhaps the future for many crypts does not have to be so bleak.

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4] [5]

 

Toxic Nectar

35523565_2235120153181504_7723861579292213248_o.jpg

I was introduced to the concept of toxic nectar thanks to a species of shrub quite familiar to anyone who has spent time in the Appalachian Mountains. Locals will tell you to never place honeybee hives near a patch of rosebay (Rhododendron maximum) for fear of so-called "mad honey." Needless to say, the concept intrigued me.

A quick internet search revealed that this is not a new phenomenon either. Humans have known about toxic nectar for thousands of years. In fact, honey made from feeding bees on species like Rhododendron luteum and R. ponticum has been used more than once during times of war. Hives containing toxic honey would be placed along known routs of Roman soldiers and, after consuming the seemingly innocuous treat, the soldiers would collapse into a stupor only to be slaughtered by armies lying in wait.

  Rhododendron luteum

Rhododendron luteum

The presence of toxic nectar seems quite confusing. The primary function of nectar is to serve as a reward for pollinators after all. Why on Earth would a plant pump potentially harmful substances into its flowers?

It is worth mentioning at this point that the Rhododendrons aren't alone. A multitude of plant species produce toxic nectar. The chemicals that make them toxic, though poorly understood, vary almost as much as the plants that make them. Although there have been repeated investigations into this phenomenon, the exact reason(s) remain elusive to this day. Still, research has drummed up some interesting data and many great hypotheses aimed at explaining the patterns.

 Catalpa nectar has been shown to deter some ants and butterflies but not large bees.

Catalpa nectar has been shown to deter some ants and butterflies but not large bees.

The earliest investigations into toxic nectar gave birth to the pollinator fidelity hypothesis. Researchers realized that meany bees appear to be less sensitive to alkaloids in nectar than are some Lepidopterans. This led to speculation that perhaps some plants pump toxic compounds into their nectar to deter inefficient pollinators, leading to more specialization among pollinating insects that can handle the toxins.

Another hypothesis is the nectar robber hypothesis. This hypothesis is quite similar to the pollinator fidelity hypothesis except that it extends to all organisms that could potentially rob nectar from a flower without providing any pollination services. As such, it is a matter of plant defense.

 The nectar of  Cyrilla racemiflora  is thought to be toxic to some bees.

The nectar of Cyrilla racemiflora is thought to be toxic to some bees.

Others feel that toxic nectar may be less about pollinators or nectar robbers and more about microbial activity. Sugary nectar can be a breeding ground for microbes and it is possible that plants pump toxic compounds into their nectar to keep it "fresh." If this is the case, the antimicrobial benefits could outweigh the cost to pollinators that may be harmed or even deterred by the toxic compounds.

Finally, it could be that toxic nectar may have no benefit to the plant whatsoever. Perhaps toxic nectar is simply the result of selection for defense compounds elsewhere in the plant and therefore is expressed in the nectar as a result of pleiotropy. If this is the case then toxic nectar might not be under as strong selection pressures as is overall defense against herbivores. If so, the plants may not be able to control which compounds eventually end up in their nectar. Provided defense against herbivores outweighs any costs imposed by toxic nectar then plants may not have the ability to evolve away from such traits.

 Where Spathodea campanulata is invasive, its nectar causes increased mortality in native bee hives.

Where Spathodea campanulata is invasive, its nectar causes increased mortality in native bee hives.

So, where does the science land us with these hypotheses? Do the data support any of these theories? This is where things get cloudy. Despite plenty of interest, evidence in support of the various hypotheses is scant. Some experiments have shown that indeed, when given a choice, some bees prefer non-toxic to toxic nectar. Also, toxic nectar appears to dissuade some ants from visiting flowers, however, just as many experiments have demonstrated no discernible effect on bees or ants. What's more, at least one investigation found that the amount of toxic compounds within the nectar of certain species varies significantly from population to population. What this means for pollination is anyone's' guess.

It is worth noting that most of the pollination-related hypotheses about toxic nectar have been tested using honeybees. Because they are generalist pollinators, there could be something to be said about toxic nectar deterring generalist pollinators in favor of specialist pollinators. Still, these experiments have largely been done in regions where honeybees are not native and therefore do not represent natural conditions.

Simply put, it is still too early to say whether toxic nectar is adaptive or not. It could very well be that it does not impose enough of a negative effect on plant fitness to evolve away from. More work is certainly needed. So, if you are someone looking for an excellent thesis project, here is a great opportunity. In the mean time, do yourself a favor and don't eat any mad honey.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4] [5] [6]

 

 

Resisting the Wind

Have you ever wondered how some plants can withstand heavy winds? At lease one group, the cattails, produce specialized support structures within their cells to cope with winds. This is great, especially when growing near a large, windy water source.

A team of researchers recently took a much closer look at the leaf cells of a variety of cattail species (genus Typha). For decades, there has been knowledge of fibers that traverse the air chambers within the cells. These have largely been ignored but as it turns out, they indeed serve a purpose.

 (A) Longitudinal section showing the fibre cables anchored in diaphragms composed of aerenchyma tissue. (B) Longitudinal section showing the fibre cables anchored in diaphragms composed of aerenchyma tissue. (C) Cross section. The thick ventral (v)and dorsal (d) surfaces of the leaf are separated by thick partitions (P) that run the length of the leaf. Thin diaphragms (D) connected perpendicular to the thick partitionsare traversed by very fine fibre cables (FC), which are anchored to them. This construction has often been compared to sandwich-type construction, giving a low-density structure of high stiffness and strength (Rowlatt and Morshead, 1992)

(A) Longitudinal section showing the fibre cables anchored in diaphragms composed of aerenchyma tissue. (B) Longitudinal section showing the fibre cables anchored in diaphragms composed of aerenchyma tissue. (C) Cross section. The thick ventral (v)and dorsal (d) surfaces of the leaf are separated by thick partitions (P) that run the length of the leaf. Thin diaphragms (D) connected perpendicular to the thick partitionsare traversed by very fine fibre cables (FC), which are anchored to them. This construction has often been compared to sandwich-type construction, giving a low-density structure of high stiffness and strength (Rowlatt and Morshead, 1992)

As any good engineer will tell you, if a structure is to remain sound, it needs multiple avenues in which stress can be redistributed. The same goes for living structures like leaves. The fibers are arranged within the cells makes them quite strong under tension. In this way, multiple load paths are created to distribute the stress of high winds on the leaves. We like to take credit for most of our ideas but, time and again, nature beat us to it first.

Photo Credit: [1] [2]

Further Reading: [1]

What Are Plants Made Of?

Have you ever thought about what plants are made of? I mean, really thought about it. Strip away all the splendor and glory of all the different plant species on this planet and really take a close look at how plants grow and make more plants. It is a fascinating realm and it all has to do with photosynthesis. To go from photons given off by our nearest star to a full grown plant is quite the journey and, at the end of that journey, you may be surprised to learn what plants are all about.

It starts with photons. Leaving the sun they travel out into the universe. Some eventually collide with Earth and make their way to the surface. Plants position their leaves to absorb these photons. Energy from the photons is used to split water molecules inside the chloroplasts. In the process of splitting water, oxygen is released as a byproduct (thanks plants!). Splitting water also releases electrons and hydrogen ions.

These electrons and hydrogen ions are used to make energy in the form of ATP. Along with some electrons, ATP is then used in another cycle known as the Calvin cycle. The point of the Calvin cycle is to take in CO2 and use the energy created prior to reduce carbon molecules into chains of organic molecules. Most of the carbon in a plant comes from the intake of CO2. Through a series of steps (I will spare you the details) plants piece together carbon atoms into long chains. Some of these chains form glucose and some of that glucose gets linked together into cellulose.

Cellulose is the main structural component of plant cells. From the smallest plants in the world (genus Wolffia) all the way up to the largest and tallest redwoods and sequoias (incidentally some of the largest organisms to have ever existed on this planet) , all of them are built out of cellulose. So, in essence, all the plant life you see out there is literally built from the ground up by carbon originating from CO2 gas. Pretty incredible stuff, wouldn't you agree?

The Trumpet Creeper

3744348096_997dfdde3c_o.jpg

With its impressive bulk and those stunning tubular red flowers, one would be excused for thinking that the trumpet creeper (Campsis radicans) was a tropical vine. Indeed, the family to which it belongs, Bignoniaceae, is largely tropical in its distribution. There are a handful of temperate representatives, however, and the trumpet creeper is one of the most popular. Its beauty aside, this plant is absolutely fascinating.

As many of you probably know, the trumpet creeper can reach massive proportions. In the garden, this can often result in collapsed structures as its weight and speed of growth is something few adequately prepare for. In the wild, I most often see this vine in somewhat disturbed forests, usually near a floodplain. As such, it is supremely adapted to take a hit and keep on growing year after year.

4351466002_1492803b16_o.jpg

One of the many reasons this plant performs so well both where it is native and where it is not is that it recruits body guards. This is easy to witness in a garden setting as the branches and especially the flowers are frequently crawling with ants. Trumpet creepers trade food for protection via specialized organs called extrafloral nectaries. These structures secrete sugary nectar that is readily sucked up by tenacious ants. When a worker ant finds a vine, more workers are soon to follow. 

Amazingly for a temperate plant, trumpet creepers produce more extrafloral nectaries of all four categories - petiole, calyx, corolla, and fruit. What this means is that all of the important organs are covered in insects that viciously attack anything that might threaten this sugary food supply. Hassle one of these vines at your own peril. With its photosynthetic and reproductive structures protected, trumpet creepers make a nice living once established.

Reproduction is another fascinating aspect of trumpet creeper biology. A closer inspection of the floral anatomy will reveal a bilobed stigma. Amazingly, this stigma has the ability to open and close as potential pollinators visit the flowers. Stigmatic movement in the trumpet creeper has attracted a bit of attention from researchers over the years. What is its function?

Evidence suggests that the opening and closing of the lobed stigma is way of increasing the chances of pollination. Touch alone is not enough to trigger the movement. However, when researchers dusted pollen onto the stigma, then it began to close. What's more, this action happens within 15 to 60 seconds. Amazingly, there appears to be a threshold to whether the stigma stays closed or reopens after 3 hours or so.

080721tc.jpg

It turns out, the threshold seems to depend on the amount of pollen being deposited. Only after 350 grains found their way onto the stigma did it close permanently. Experts feel that this a means by which the plant ensured ample seed set. If too few pollen grains end up on the stigma, the plant risks not having all of its ovules fertilized. By permanently closing after enough pollen grains are present, the plant can ensure that the pollen grains can germinate and fertilize the ovules without being brushed off.

It is interesting to note that the flowers frequently remain on the plant after they have been fertilized. This likely serves to maintain a largely floral display that continues to attract pollinators until most of the flowers have been pollinated. Speaking of pollinators, observations have revealed that the trumpet creeper is pollinated primarily by ruby-throated hummingbirds. Although insects like bumblebees frequently visit these blooms, bringing pollen with them in the process, hummingbirds, on average, bring and deposit 10 times as much pollen as any other visitor. And, considering the threshold on pollen mentioned above, trumpet creeper appears to have evolved a pollination syndrome with these lovely little birds.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] [4]

Big Things Come In Small Packages

il_570xN.1271356583_c10y.jpg

Meet Blossfeldia liliputana, the smallest species of cactus in the world. With a maximum diameter of only 12 mm, this wonderful succulent would be hard to spot tucked in among the nooks and crannies of rock outcrops. Its species name "liliputana" is a reference to the fictional island of Liliput (Gulliver's Travels) whose inhabitants were said to be rather small. If its size alone wasn't interesting in and of itself, the biology of B. liliputana is also downright bizarre.

B. liliputana is native to arid regions between southern Bolivia and northern Argentina. It appears to prefer growing wedged between cracks in rock as these are usually the spots where just enough soil builds up to put down its roots. Root formation, however, does not happen for quite some time. Most often new individuals bud off from the parent plant. They emerge not from the base, but rather from apical tissues, yet another unique feature of this cactus. What's more, this cactus produces no spines. Instead, its numerous areoles are covered in a dense layer of trichomes that are rather felt-like to the touch.

As you can clearly see, this species is small. It only ever becomes conspicuous when it comes time to flower. Imagine a bunch of tiny white to pink cactus flowers poking out of a crevice. It must be a remarkable sight to see in person. Despite their showy appearance, its is believed that most are self-fertilized.

As mentioned, the size of this cactus isn't the only interesting thing about its biology. B. liliputana is categorized as a poikilohydric organism, meaning it doesn't have the ability to regulate its internal water content. Researchers have found that individual plants can lose up to 80% of their weight in water and can maintain that state for as long as two years without any negative effects. As such, colonies of these tiny cacti often appear shrunken or squished. Once the rains arrive, however, it springs back to its original rounded shape with seemingly no issues. Amazingly, a significant amount of water uptake happens via the fuzzy areoles that cover its surface, hence it does not harm the plant to hold off growing roots for quite some time. 

Speaking of water regulation, B. liliputana holds another record for having the lowest density of stomata of any terrestrial autotrophic vascular plant. Stomata are the pores in which plants regulate water and gas exchange so having so few may have something to do with why this species loses and gains water to such a degree that would kill most other vascular plant species.

Another peculiar quality of this cactus are its seeds. Unlike all other cacti whose seeds are hard and relatively smooth, the seeds of B. liliputana are hairy. Attached to each seed is a small fleshy structure called an aril, which aids in seed dispersal. As it turns out, B. liliputana relies on ants as its main seed dispersers. Ants attracted to the fleshy aril drag the seeds back to their nests, remove and eat the aril, and then discard the seed. This is often good news for the cactus because its seeds end up in nutrient-rich ant middens protected from both the elements and seed predators, often in much more suitable conditions for germination.

Blossfeldia_liliputana_20130512.jpg

Needless to say, B. liliputana is a bit of an oddball as far as cacti are concerned. Its highly derived features coupled with its bizarre biology has made it difficult for taxonomists to elucidate its relationship to the rest of the cactus family. It certainly deserves its own genus, to which it is the only member, however, it has been added to and removed form a handful of cactus subfamilies over the years. The most recent genetic analyses suggests that it is unique enough to warrant its own tribe within Cactaceae - Blossfeldieae.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3]

Aloe or Agave?

Aloe vs agave.jpg

Convergent evolution is the process by which unrelated organisms evolve similar traits in response to similar environmental constraints. One amazing example of convergent evolution has occurred among the Aloe and Agave. These two distinct lineages are separated both in space and time and yet they often look so similar that it can be hard for the average person to tell them apart. With that in mind, lets consider the similarities and differences between these two lineages.

To start, Aloe and Agave hail from two completely different spots on the botanical family tree. Each also has its own unique geographic origin. Agave is a New World genus with species ranging in their distribution from tropical South America north into arid portions of North America. Genetic analysis places the genus Agave in the family Asparagaceae.

  Agave americana  in bloom

Agave americana in bloom

Aloe, on the other hand, enjoys an Old World distribution, from Africa and Madagascar to the Arabian Peninsula as well as many islands scattered throughout the Indian Ocean. Taxonomically speaking, Aloe has undergone more than a few revisions through time, however, recent genetic work suggests that the Aloe belong to the family Asphodelaceae.

Experts believe that the lineages that gave rise to these two distinct genera branched off from a common ancestor some 93 million years ago. Despite all of that intervening time and space, the rigors of their arid habitats have managed to shape these plants in strikingly similar ways. Morphologically speaking, there is a lot of superficial similarity between Aloe and Agave.

  Aloe hereroensis in situ

Aloe hereroensis in situ

Both groups exhibit water-storing, succulent leaves arranged in rosettes. These leaves are often adorned with spines or other protrusions aimed at deterring herbivores. Both groups also utilize CAM photosynthesis for their energy needs. When it comes time to flower, both groups frequently produce brightly colored, tubular flowers arranged at the tip of long stalks.

It is worth noting that the harsh environments that have shaped these two plant lineages also seems to have induced a backup plan for reproduction. Both Aloe and Agave produce tiny offshoots called "pups." These pups gain nourishment from the parent plant until they are large enough to fend for themselves. All pups are clones but if the parent plant had what it takes to survive in that spot, there is a good chance that its cloned offspring will as well. That way, even if sexual reproduction fails, these cloned progeny will get another shot.

Despite all of this convergence, these two lineages nonetheless exhibit vastly different developmental pathways and thus there are plenty of differences separating the two. For starters, slice into the leaves of each type and you will quickly find one major morphological difference. As many already know, Aloe leaves are largely filled with a gooey pulp and not much else. Aloe leaves function as water storage organs. Agave also store plenty of liquid in their leaves, however, they also produce numerous long strands of fiber that provide much more structural integrity.

 Cross section of an Aloe leaf showing gelatinous pulp.

Cross section of an Aloe leaf showing gelatinous pulp.

 Agave leaf showing fibrous interior.

Agave leaf showing fibrous interior.

Aloe and Agave each have evolved their own reproductive strategies as well. Aloe are perennial bloomers. Under the right conditions, many Aloe species will produce a profusion of flower stalks year after year. The stalks emerge from between the leaves and are largely pollinated by birds and insects in their native habitats. Agave, on the other hand, are monocarpic meaning they invest all of their energy into one single bloom. The Agave flowering stalk emerges from the center of the rosette and are pollinated by myriad insects, birds, and even bats. After flowering is complete, the main Agave plant dies.

 Aloe flowers

Aloe flowers

 Agave flowers

Agave flowers

Convergent evolution will never cease to amaze me. Despite millions of years and hundreds of miles separating these two lineages, Aloe and Agave have nonetheless been shaped in similar ways by similar environmental conditions.

Photo Credits: Wikimedia Commons

Further Reading: [1]

How Aroids Turn Up the Heat

4197953814_0f2f22ce07_o.jpg

A subset of plants have evolved the ability to produce heat, a fact that may come as a surprise to many reading this. The undisputed champions of botanical thermogenesis are the aroids (Araceae). Exactly why they do so is still the subject of scientific debate but the means by which heat is produced is absolutely fascinating.

The heat producing organ of an aroid is called the spadix. Technically speaking, a spadix is a spike of minute flowers closely arranged around a fleshy axis. All aroid inflorescences have one and they come in a wide variety of shapes, colors, and textures. To produce heat, the spadix is hooked up to a massive underground energy reserve largely in the form of carbohydrates or sugars. The process of turning these sugars into heat is rather complex and surprisingly animal-like.

 Cross section of a typical aroid inflorescence with half of the protective spathe removed. The spadix is situated in the middle with a rings of protective hairs (top), male flowers (middle), and female flowers (bottom).

Cross section of a typical aroid inflorescence with half of the protective spathe removed. The spadix is situated in the middle with a rings of protective hairs (top), male flowers (middle), and female flowers (bottom).

It all starts with a compound we are rather familiar with - salicylic acid - as it is the main ingredient in Aspirin. In aroids, however, salicylic acid acts as a hormone whose job it is to initiate both the heating process as well as the production of floral scents. It signals the mitochondria packed inside a ring of sterile flowers located at the base of the spadix to change their metabolic pathway.

In lieu of their normal metabolic pathway, which ends in the production of ATP, the mitochondria switch over to a pathway called the "Alternative Oxidase Metabolic Pathway." When this happens, the mitochondria start burning sugars using oxygen as a fuel source. This form of respiration produces heat.

 Thermal imaging of the inflorescence of  Arum maculatum .

Thermal imaging of the inflorescence of Arum maculatum.

As you can imagine, this can be a costly process for plants to undergo. A lot of energy is consumed as the inflorescence heats up. Nonetheless, some aroids can maintain this costly level of respiration intermittently for weeks on end. Take the charismatic skunk cabbage (Symplocarpus foetidus) for example. Its spadix can reach temperatures of upwards of 45 °F (7 °C) on and and off for as long as two weeks. Even more incredible, the plant is able to do this despite freezing ambient temperatures, literally melting its way through layers of snow.

For some aroids, however, carbohydrates just don't cut it. Species like the Brazilian Philodendron bipinnatifidum produce a staggering amount of floral heat and to do so requires a different fuel source - fat. Fats are not a common component of plant metabolisms. Plants simply have less energy requirements than most animals. Still, this wonderful aroid has converged on a fat-burning metabolic pathway that puts many animals to shame. 

 The inflorescence of  Philodendron bipinnatifidum  can reach temps as high as 115 °F (46 °C)

The inflorescence of Philodendron bipinnatifidum can reach temps as high as 115 °F (46 °C)

P. bipinnatifidum stores lots of fat in sterile male flowers that are situated between the fertile male and female flowers near the base of the spadix. As soon as the protective spathe opens, the spadix bursts into metabolic action. As the sun starts to set and P. bipinnatifidum's scarab beetle pollinators begin to wake up, heat production starts to hit a crescendo. For about 20 to 40 minutes, the inflorescence of P. bipinnatifidum reaches temperatures as high as 95 °F (35 °C) with one record breaker maxing out at 115 °F (46 °C)! Amazingly, this process is repeated again the following night.

It goes without saying that burning fat at a rate fast enough to reach such temperatures requires a lot of oxygen. Amazingly, for the two nights it is in bloom, the P. bipinnatifidum inflorescence consumes oxygen at a rate comparable to that of a flying hummingbird, which are some of the most metabolically active animals on Earth.

 The world's largest inflorescence belongs to the titan arum ( Amorphophallus titanum ) and it too produces heat.

The world's largest inflorescence belongs to the titan arum (Amorphophallus titanum) and it too produces heat.

Again, why these plants go through the effort of heating their reproductive structures is still a bit of a mystery. For most, heat likely plays a role in helping to volatilize floral scents. Anyone that has spent time around blooming aroids knows that this plant family produces a wide range of odors from sweet and spicy to downright offensive. By warming these compounds, the plant may be helping to lure in pollinators from a greater distance away. It is also thought that the heat may be an attractant in and of itself. This is especially true for temperate species like the aforementioned skunk cabbage, which frequently bloom during colder months of the year. Likely both play a role to one degree or another throughout the aroid family.

What we can say is that the process of plant thermogenesis is absolutely fascinating and well worth deeper investigation. We still have much to learn about this charismatic group of plants.

LEARN MORE ABOUT AROID POLLINATION HERE

Photo Credits: [1] [2] [3] [4] [5]

Further Reading: [1] [2] [3] [4] [5] [6] [7] [8]