The Traveler's Palm

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This nifty looking tree is commonly referred to as the traveler's palm (Ravenala madagascariensis). In reality, it is not a palm at all but rather a close cousin of the bird of paradise plants (Strelitziaceae). It is endemic to Madagascar and the only member of its genus. Even more fascinating is its relationship with another uniquely Madagascan group - the lemurs. But first we must ask, what's in a name?

The name "traveler's palm" has two likely explanations. The first has to do with the orientation of that giant fan of leaves. The tree is said to align its photosynthetic fan in an east-west orientation, which can serve as a crude compass, allowing weary travelers to orient themselves. I found no data to support this. The other possibility comes from the fact that this tree collects a lot of water in its nooks and crannies. Each of its hollow leaf bases can hold upwards of a quart of rain water! Get to it quick, though, because these water stores soon stagnate.

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Flowers are produced between the axils of the leaves and closely resemble those of its bird of paradise cousins. Closer observation will reveal that they are nonetheless unique. For starters, they are large and contained within stout green bracts. Also, they are considerably less showy than the rest of the family. They don't produce any strong odors but they do fill up with copious amounts of sucrose-rich nectar. Finally, the flowers remain closed, even when mature and are amazingly sturdy structures. It may seem odd for a plant to guard its flowers so tightly until you consider how they are pollinated.

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It seems fitting that an endemic plant like the traveler's palm would enter into a pollination syndrome with another group of Madagascar endemics. As it turns out, lemurs seem to be the preferred pollinators of this species. Though black lemurs, white fronted lemurs, and greater dwarf lemurs have been recorded visiting these blooms, it appears that the black-and-white ruffed lemur manages a bulk of the pollination services for this plant.

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Watching the lemurs feed, one quickly understands why the flowers are so stout. Lemurs force open the blooms to get at the nectar inside. The long muzzles of the black-and-white ruffed lemur seem especially suited for accessing the energy-rich nectar within. The flowers themselves seem primed for such activity as well. The enclosed anthers are held under great tension. When a lemur pries apart the petals, the anthers spring forward and dust its muzzle with pollen. Using both its hands and feet, the lemur must wedge its face down into the nectar chamber in order to take a sip. In doing so, it inevitably comes into contact with the stigma. Thus, pollination is achieved. Once fertilized, the traveler's palm produces seeds that are covered in beautiful blue arils.

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All in all, this is one unique plant. Though its not the only plant to utilize lemurs as pollinators, it is nonetheless one of the more remarkable examples. Its stunning appearance has made it into something of a horticultural celebrity and one can usually find the traveler's palm growing in larger botanical gardens around the world. Though the traveler's palm itself is not endangered, its lemur pollinators certainly are. As I have said time and again, plants do not operate in a vacuum. To save a species, one must consider the entirety of its habitat. This is why land conservation is so vitally important. Support a land conservancy today!

Photo Credits: [1] [2]

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

 

Cockroaches & Unexpected Partnerships

Say "cockroach" and most people will start to squirm. These indefatigable insects are maligned the world over because of a handful of species that have settled in quite nicely among human habitats. The world of cockroaches is far more diverse than most even care to realize, and where they occur naturally, these insects provide important ecological services. For instance, over the last decade or so, researchers have added pollination and seed dispersal to the list of cockroach activities. 

That's right, pollination and seed dispersal. It may seem odd to think of roaches partaking in such interactions but a study published in 2008 provides some of the first evidence that roaches are doing more with plants than eating their decaying tissues. After describing a new species of Clusia in French Guiana, researchers set out to investigate what, if anything, was pollinating it. The plant was named Clusia sellowiana and its flowers emitted a strange scent. 

Cockroach pollinating  C. sellowiana

Cockroach pollinating C. sellowiana

The source of this scent was the chemical acetoin. It seemed to be a rather attractive scent as a small variety of insects were observed visiting the flowers. However, only one insect seemed to be performing the bulk of pollination services for this new species - a small cockroach called Amazonia platystylata. It turns out that the roaches are particularly sensitive to acetoin and although they don't have any specific anatomical features for transferring pollen, their rough exoskeleton nonetheless picks up and deposits ample amounts of the stuff. 

It would appear that C. sellowiana has entered into a rather specific relationship with this species of cockroach. Although this is only the second documentation of roach pollination, it certainly suggests that more attention is needed. This Clusia isn't alone in its interactions with cockroaches either. As I hinted above, roaches can now be added to the list of seed dispersers of a small parasitic plant native to Japan. 

 (A) M. humile fruit showing many minute seeds embedded in the less juicy pulp. (B) Fallen fruits. (C) Blattella nipponica feeding on the fruit. (D) Cockroach poop with seeds. (E) Stained cockroach-ingested seeds

Monotropastrum humile looks a lot like Monotropa found growing in North America. Indeed, these plants are close cousins, united under the family Ericaceae. Interestingly enough, it was only recently found that camel crickets are playing an important role in the seed dispersal of this species. However, it looks like they aren't the only game in town. Researchers have also found that a forest dwelling cockroach called Blattella nipponica serves as a seed disperser as well. 

The roaches were observed feeding on the fruits of this parasitic plant, consuming pulp and seed alike. What's more, careful observation of their poop revealed that seeds of M. humile passed through the digestive tract unharmed. Cockroaches can travel great distances and therefore may provide an important service in distributing the seeds of a rather obscure parasitic plant. To think that this is an isolated case seems a bit naive. It seems to me like we should pay a little more attention to what cockroaches are doing in forests around the world. 

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

Further Reading: [1] [2]

Resin Midges, Basal Angiosperms, and a Strange Pollination Syndrome

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When we try to talk about clades that are "basal" or "sister" to large taxonomic groups, your average listener either consciously or unconsciously thinks "primitive." Primitive has connotations of something that under-developed or unfinished. This is simply not the case. Take, for instance, a family of basal angiosperms called Schisandraceae.

This family is nestled within the order Austrobaileyales, which, along with a small handful of other families, represent the earliest branches of the angiosperm family tree still alive today.  To call them primitive, however, would be a serious misnomer. Because they diverged so early on, these lineages represent serious success stories in flowering plant evolution, having survived for hundreds of millions of years. Instead, we must think of them as fruitful early experiments in angiosperm evolution.

Floral morphology of and interaction between midge and their larvae (white arrows) in Illicium dunnianum

Still, the proverbial proof is in the pudding and if there was any sort of physical evidence one could put forth to remove our hierarchical prejudices about the taxonomic position of these plants, it would have to be their bizarrely specific pollination syndromes.  Members of the family Schisandraceae have entered into intense relationships with a group of flies known as midges and their interactions are anything but primitive. 

We will start with two species of plant native throughout parts of Asia. Meet as Illicium dunnianum and Illicium tsangii. More will be familiar with this genus than they may realize as Illicium gives us the dreaded star anise flavor our grandparents liked to sneak into our cookies as kids (but I digress). These particular species, however, have more to offer the world than flavoring. They are also very important plants for a group of gall midges in the genus Clinodiplosis.

The midges cannot reproduce without I. dunnianum or I. tsangii. You see, these midges lay their eggs within the flowers of these plants and, in doing so, end up pollinating them in the process. At first glance it may seem like a very one-sided relationship. Female midges deposit their eggs all along the carpels packed away inside large, fleshy whorl of tepals. As the midges crawl all over the reproductive organs looking for a suitable place to lay, they inevitably pick up and deposit pollen. 

Floral morphology and interaction between midge larvae (white arrows) in  Illicium tsangii

This is not the end of this relationship though. After eggs have been deposited, something strange happens to the Illicium flowers. For starters, they develop nursery chambers around the midge larvae. Additionally, their tepals begin producing heat. Enough heat is produced to keep the nursery chamber temperature significantly warmer than the ambient air temperature. What's more flower heating intensifies throughout the duration of fruit development. It was originally hypothesized that this heating had something to do with floral odor volatilization and seed incubation, however, experiments have shown that at least seed development in these two shrubs is not influenced by floral heat in any major way. The same cannot be said for the midge larvae. 

As the flowers mature and give way to developing seeds, the midge larvae are hard at work feeding on tiny bits of the flowers themselves. When researchers looked at midge larvae development on these Illicium species, they found that they were completely dependent upon the floral heat for survival. Any significant drop in temperature caused them to die. Essentially, the plants appear to be producing heat more for the midges than for themselves. It may seem odd that these two plants would invest so much energy to heat their flowers so that midge larvae feeding on their tissues can survive but such face-value opinions rarely stand in ecology.

One must not forget that those larvae grow up to be adult midges that will go on to pollinate the Illicium flowers the following season. Although the plants are taking a bit of a hit by allowing the larvae to develop within their tissues, they are nonetheless ensuring that enough pollinators will be around to repeat the process again. If that wasn't cool enough, the relationship between each of these plants and their pollinators are rather specific and the authors of at least one paper believe that the midges that pollinate each species are new to science. 

Now, if I haven't managed to convince you that this angiosperm sister lineage is anything but primitive, then let's take a look at another genus within the family Schisandraceae that have taken this midge pollination syndrome to the next level. This story also takes place in Asia but instead involves a genus of woody vines known as Kadsura

Like the Illicium we mentioned earlier, a handful of Kadsura species rely on midges for pollination. The way in which they go about maintaining this relationship is a bit more involved. The midges that are attracted by Kadsura flowers are known as resin midges and their larvae live off of plant resins. The flowers of Kadsura are another story entirely. They are as odd as they are beautiful. 

Flowers, pollinators ,and their larvae (white arrows) in  Kadsura heteroclita .

Flowers, pollinators ,and their larvae (white arrows) in Kadsura heteroclita.

In male flowers, stamens are arranged in dense, cone-like structures called androecia whereas the female flowers contain a compact shield-like structure with the uppermost part of the stigma barely emerging. This is called a gynoecium. Even weirder, the male flowers of one particularly strange species, Kadsura coccinea, produce large, swollen inner tepals. 

Once Kadsura flowers begin to open, visiting midges are not far behind. Male flowers seem to attract more midges than female flowers and it is thought that this has to do with varying amounts of special attractant chemicals produced by the flowers themselves. Regardless, midges set to work exploring the blooms with males looking for mates and females looking for a place to lay their eggs. 

When a suitable spot has been found, females will deposit their eggs into the floral tissues with their ovipositor. The wounded plant tissues immediately begin producing resin, not unlike a wounded pine tree. In the case of K. coccinea, it would appear that the oddly swollen tepals are specifically targeted by female midges for egg laying. They too produce resin upon having eggs laid within. 

The oddball flowers of Kadsura coccinea showing swollen tepals.

The function of plant resins in many cases are to fight off pathogens. From beetles to fungi, resin helps plug up and seal off wounds. This does not seem to be the case in the Kadsura-midge relationship though. The so-called "brood chambers" within the floral tissues go on producing resin for upwards of 6 days after the midge eggs were laid. Eventually the floral parts whither and drop off but the midge larvae seem to be quite happy in their resin-filled homes. 

As it turns out, the resin midge larvae feed on the viscous resin as their sole food source. Instead of trying to ward off these pesky little insects, the plants seem to be encouraging them to raise their offspring within! Just as we saw in the Asian Illicium, these Kadsura vines seem to be providing brood sites for their pollinators. Also, just as the Illicium-midge relationship thought to be species specific, each species of Kadsura appears to have its own specific species of resin midge pollinator! K. coccinea even goes as far as to produce tepals specifically geared towards raising midge larvae, thus keeping them away from their more valuable reproductive organs. In return for the nursery service, Kadsura have their pollinators all to themselves.

Pollination mutualisms in which plants trade raising larvae for pollen transfer are extremely derived and some of the most specialize plant/animal interactions on the planet. To find such relationships in these basal or sister lineages is living proof that these plants are anything but primitive. In the energy-reproductive investment trade-off, it appears that ensuring ample pollinator opportunities far outweighs the cost of providing them with nursery chambers. It is remarkable to think just how intertwined the relationships between these plants and there pollinators truly are. Take that, plant taxonomic prejudices! 

Photo Credits: [1] [2]

Further Reading: [1] [2] 

 

A Common Plant With An Odd Pollination Mechanism

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Pollination is not an altruistic enterprise. Each party involved is trying to maximize its gains while minimizing its losses. Needless to say, cheaters abound in natural systems. As such, plants have gone to great lengths to ensure that their reproductive investments pay off in the long run. Take, for instance, the case of the fragrant water-lily (Nymphaea odorata). 

Most of us have encountered this species at some point in our lives. Those who have often remark on the splendor of their floral displays. Certainly this is not lost on pollinators either. Coupled with their aromatic scent, these aquatic plants must surely be a boon to any insect looking for pollen and nectar. Still, the flowers of the fragrant water-lily take no chances.

Close observation will reveal an interesting pattern in the blooming cycle of this water-lily. On the first day that the flowers open, only the female portions are mature. The structure itself is bowl-like in shape. Filling this stigmatic bowl is a viscous liquid. After the first day, the flowers close for the evening and reopen to reveal that the stigma is no longer receptive and instead, the anthers have matured.

Many insects will visit these floating flowers throughout the blooming period. Everything from flies, to beetles, and various sorts of bees have been recorded. Seed set in this species is pollen limited so any insect visiting a female flower must deposit pollen if reproduction is to be achieved. This is where that bowl of sticky liquid comes into play. The liquid itself is rather unassuming until you see an insect fall in.

Due to the presence of surfactants, any insect that falls into the fluid immediately sinks to the bottom. The flowers seem primed to encourage this to happen too. The flexible inner stamens that surround the bowl bend under the weight of heavier insects, thus dumping them into the liquid below. Only by observing this process under extreme magnification does all of this make sense.

The liquid within the bowl essentially washes off any pollen that a visiting insect had stuck to its body. As the pollen falls off, it drifts down to the bottom of the bowl where it contacts the receptive stigma. Thus, cross-pollination is achieved. Most of the time, insect visitors are able to crawl out without any issue. However, the occasional insect will drown within the fluid. Alas, that is no sweat off the water-lily's back. Having dropped off the pollen it was carrying, it is of little use to that flower anymore.

Once a water-lily flower has been fertilized, its stem begins to curl up like a spring. This draws the ovaries underwater where they can develop in relative safety. It also ensures that, upon maturing, the seeds are more likely to find a suitable underwater site for germination. To think that this drama plays out time and time again unbeknownst to the casual observer is something I find endlessly fascinating about the natural world.

Photo Credit: [1] [2]

Further Reading: [1] [2]

Bird Pollination Of The Bird Of Paradise

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Who hasn't stared in wonderment at the inflorescence of a bird of paradise? One doesn't need too much of an imagination to understand how these plants got this common name. Flowers, however, did not evolve in response to our aesthetic tastes. They are solely for sex and in the case of bird of paradise, Strelitzia reginae, pollination involves birds.

In its native range in South Africa, S. reginae is pollinated by sunbirds, primarily the Cape weaver (Ploceus capensis). That alluring floral morphology is wonderfully adapted to maximize the chances of successful cross-pollination by their avian visitors. Cape weavers are looking for a sip of energy rich nectar. To get at said nectar, the birds must perch on the inflorescence. Not any position will do either.

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To get their reward, the birds must perch so that their beaks are at just the right angle to reach down into the floral tubes. The plant ensures this by providing a convenient perch. Those fused blue petals are structurally reinforced and actually serve as a convenient perch! Upon alighting on the perch, the hidden anthers are thrust outward from their resting chamber, brushing up against the bird's feet in the process. The Cape weaver doesn't move around much once on the flower so self pollination is minimized.

When the bird visits another plant, the process is repeated and pollination is achieved. Seed set is severely pollen limited. This is a good thing considering how popular they are in cultivation. Plants growing outside of South Africa rarely set seed without a helping hand. However, here in North America, some birds seemed to have figured out how to get at bird of paradise nectar.

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Observations made in southern California found that at least one species of warbler, the common yellowthroat (Geothlypis trichas), not only made regular visits to a stand of S. reginae, it also seemed to figure out the proper way to do so. Individuals were seen perching on the floral perch and drinking the nectar. They were pretty effective visitors at that. Of the 14,400 inflorescence found within the study area, 88% of them produced viable seed! It seems that far from its native range, S. reginae has a friend in at least one New World warbler. Armed with this knowledge, land owners should be vigilant to ensure this plant doesn't become a problem in climates suitable for its growth.

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

Further Reading: [1]

 

A Bat-Pollinated Passion Flower From Ecuador

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Say "hello" to one of Passiflora's most recent additions, the bat-pollinated Passiflora unipetala. The first specimens of this vine were discovered back in 2009 by Nathan Muchhala while studying flower visiting bats in northern Ecuador. It is a peculiar member of the genus to say the least. 

One of the most remarkable features of this plant are its flowers. Unlike its multi-petaled cousins, this species stands out in producing a single large petal, which is unique for not only the genus, but the whole family as well. The petal is quite large and resembles a bright yellow roof covering the anthers and stigma. At the base of the flower sits the nectar chamber. The body of the plant consists of a vine that has been observed to grow upwards of 6 meters up into the canopy.

Flowering in this species occurs at night. Their large size, irregular funnel shape, and bright yellow coloring all point to a pollination syndrome with bats. Indeed, pollen of this species has been found on the fur of at least three different bat species. Multiple observations (pictured here) of bats visiting the flowers helped to confirm. Oddly enough for a bat-pollinated plant, the flowers produce no detectable odor whatsoever. However, another aspect of its unique floral morphology is worth noting. 

The surface of the flower has an undulating appearance. Also, the sepals themselves have lots of folds and indentations, including lots of dish-shaped pockets. It is thought that these might help the flower support the weight of visiting bats. They may also have special acoustic properties that help the bats locate the flowers via echolocation. Though this must be tested before we can say for sure, other plants have converged on a similar strategy (read here and here).

As it stands currently, Passiflora unipetala is endemic to only a couple high elevation cloud forests in northern Ecuador. It has only ever been found at two locations and sadly a landslide wiped out the type specimen from which the species description was made. As such, its introduction to the world came complete with a spot on the IUCN Redlist as critically endangered. Luckily, the two localities in which this species has been found are located on privately protected properties. Let's just hope more populations are discovered in the not-too-distant future.

Photo Credits: [1] 

Further Reading: [1]

Ants As Pollinators?

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Ants interact with plants in a variety of beneficial ways. They offer protection, they provide nutrients, they even disperse seeds! When it comes to pollination, however, plants have largely gone elsewhere. That's not to say ants don't get directly involved in the sex lives of plants. At least one plant species native to Spain has been found to be pollinated by ants. Certainly there are probably more examples of ant pollination throughout the plant kingdom, we simply have to look. For example, one possible ant-pollinated plant can be found growing on the west coast of North America.

The dwarf owl's-clover (Triphysaria pusilla) is a small annual member of the broomrape family. It really is a dwarf species, rarely exceeding a few inches in height. What it lacks in size, it makes up for in abundance. Large colonies of these species can be found growing among other low statured herbs in wetter areas like spring-fed grasslands. Their tendency to produce lots of anthocyanin pigments in their tissues means that these maroon colonies really stand out. Like other members of the family, it is a facultative hemiparasite, tapping into the roots of surrounding vegetation with its roots, stealing nutrients and water as the situation demands.

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Flowering in the dwarf owl's-clover is rather inconspicuous. The dense flowering spikes produce minute, tubular, maroon-yellow flowers. It has been observed that, at any given point during the flowering season, only three flowers will have matured on any given plant. Two of these flowers mature their anthers first whereas the remaining flower matures its stigma. This is likely an adaptation for increasing the chances of cross pollination. 

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Because these flowers hardly qualify as an attractive display for more commonly encountered insect pollinators, it has been hypothesized that ants are the preferred pollinator of this species. Early work even suggested that the dense leaf arrangement facilitates ant movement to and from flowers in any given colony. Although no one has yet quantified the efficacy of ants as pollinators of this species, numerous observations of ants visiting flowers and picking up pollen have been made. Famously, such a scene was filmed for the 1981 documentary "Sexual Encounters of the Floral Kind."

Whether these visits constitute effective pollination remains to be seen. It could be that the ants are nothing more than nectar and pollen thieves. What's more, many ants produce substances from specialized glands that, among other things, destroy pollen. Until someone takes the time to study this interaction, we simply do not know. Sounds like a fun research project to me! 

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

Further Reading: [1]

More to Tall Boneset Than Meets the Eye

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For most of the growing season, tell boneset (Eupatorium altissimum) is largely overlooked. When it comes time to flower, however, it is impossible to miss. Contrasted against a sea of goldenrods, its bright white flowers really stand out. This is a hardy species, tolerating lots of sun and dry soils. It is also a boon for pollinators and is usually humming with attention. To the naked eye, it would seem that there is nothing strange going on with this species. It grows, flowers, and sets seed year after year. However, a genes eye view of tall boneset tells a vastly different story. 

A population wide study revealed that the vast majority of the tall boneset plants we encounter are females. In fact, only populations found in the Ozark Mountains were found to be sexually viable. This was quite fascinating considering how wide spread this species is in North America. A close examination of the genome revealed that sexual plants were genetically diploid whereas the female-only plants were genetically triploid. These triploid plants produce sterile male parts that either have highly deformed pollen grains or produce no pollen at all. 

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Sexual populations of tall boneset do not reproduce vegetatively. They must be cross pollinated in order to set seed. Such is not the case for the female-only populations. These plants set seed on their own without any pollen entering into the equation. The seeds they produce are essentially clones of the mother plant. Such asexual reproduction seems to be quite advantageous for these plants. For starters, they produce considerably more seed than their sexually reproducing relatives. The offspring produced from those seeds, having the same genetic makeup as their mothers, are inherently well-adapted to whatever conditions their mothers were growing in. As such, populations can readily colonize and expand, which goes a long way in explaining the female-only dominance. 

Although tall boneset really hits its stride in midwestern North America, it can be found growing throughout the eastern portion of this continent. Casual observation would never reveal such interesting population dynamics which is why single species studies are so important. Not only do we learn that much more about a beloved plant, we also gain an understanding of how plants evolve over time as well as factors one must consider should conservation measures ever need to be considered. 

Further Reading: [1] 

So Many Goldenrods, So Little Time

Nothing says late summer quite like the blooming of the goldenrods. These conspicuous members of the aster family get a bad rap because many folks blame them for causing hay fever. This is simply not true! In this video we take a closer look at a small handful of goldenrods as a way of celebrating this ecologically important group.

Music by: Artist: Ampacity

Track: Encounter One

https://ampacity.bandcamp.com

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How Plants Influence Honeybee Caste System

Is has long been known that food fed to larval honeybees influences their development and therefore their place in the hive. Larvae fed a mixture of pollen and honey, often referred to as "bee bread," develop into sterile workers whereas larvae fed special secretions termed "royal jelly" from nurses within the colony will develop into queens. Despite this knowledge, the mechanisms underpinning such drastic developmental differences have remained a mystery... until now.

A team of researchers from Nanjing University in China have uncovered the secret to honeybee caste systems and it all comes down to the plants themselves. It all has to do with tiny molecules within plants called microRNA. In eukaryotic organsisms, microRNA plays a fundamental role in the regulation of gene expression. In plants, they have considerable effects on flower size and color. In doing so, they can make floral displays more attractive to busy honeybees.

Photo Credit: [1]

Photo Credit: [1]

As bees collect pollen and nectar, they pick up large quantities of these microRNA molecules. Back in the hive, these products are not distributed equally, which influences the amount of microRNA molecules that are fed to developing larvae. The team found that microRNA molecules are much more concentrated in bee bread than they are in royal jelly. Its this difference in concentrations that appears to be at the root of the caste system.

Larvae that were fed bee bread full of microRNA molecules developed smaller bodies and reduced, sterile ovaries. In other words, they developed into the worker class. Alternatively, larvae fed royal jelly, which has much lower concentrations of microRNA, developed along a more "normal" pathway, complete with functioning ovaries and a fuller body size; they developed into queens.

All of this hints at a deep co-evolutionary relationship. The fact that these microRNA molecules not only make plants more attractive to pollinators but also influence the caste system of these insects is quite remarkable. Additionally, this opens up new doors into understanding co-evolutionary dynamics. If horizontal transfer of regulatory molecules between two vastly different kingdoms of life can manifest in such important ecological relationships, there is no telling what more is awaiting discovery. 

Further Reading: [1]

 

Birds Work a Double Shift For Osmoxylon

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Plants go to great lengths to achieve pollination. Some can be tricky, luring in pollinators with a promise of food where there is none. Others, however, really sweeten the deal with ample food reserves. At least one genus of plants has taken this to the extreme, using the same techniques for pollination as it does for seed dispersal. I present to you the genus Osmoxylon.

Comprised of roughly 60 species spread around parts of southeast Asia and the western Pacific, the genus Osmoxylon hail from a variety of habitats. Some live in the deep shade of the forest understory whereas others prefer more open conditions. They range in size from medium sized shrubs to small trees and, upon flowering, their place within the family Araliaceae becomes more apparent.

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Look closely at the flowers, however, and you might notice a strange pattern. It would appear that as soon as flowers develop, the plant has already produced berries. How could this be? Are there cleistogamous flowers we aren't aware of? Not quite. The truth, in fact, is quite peculiar. Of the various characteristics of the genus, one that repeatedly stands out is the production of pseudo-fruits. As the fertile flowers begin to produce pollen, these fake fruits begin to ripen. There aren't any seed inside. In truth, I don't think they can technically be called fruits at all. So, why are they there?

Although actual observations will be required to say for sure, the running hypothesis is that these pseudo-fruits have evolved in response to the presence of birds. They are pretty fleshy and would make a decent meal. It is thought that as birds land on the umbel to eat these pseudo-fruits, they invariably pick up pollen in the process. The bird the exchanges pollen with every subsequent plant it visits. Thus, pollination is achieved.

The relationship with birds doesn't end here. Like other members of this family, pollination results in the formation of actual fruits full of seeds. Birds are known for their seed dispersal abilities and the Osmoxylon capitalize on that as well. As such, the reproductive input of their avian neighbors is thought to be two-fold. Not only are birds potentially great pollinators, they are also great seed dispersers, taking fruits far and wide and depositing them in nutrient-rich packets wherever they poop.

Photo Credits: [1] [2]

Further Reading: [1]

Closed on Account of Weather

Alpine and tundra zones are harsh habitats for any organism. Favorable conditions are fleeting and nasty weather can crop up in the blink of an eye. Whereas animals in these habitats can take cover, plants don't have that luxury. They are stuck in place and have to deal with whatever comes their way. Despite these challenges, myriad plant species have adapted to these conditions and thrive where other plants would perish. The intense selection pressures of these habitats have led to some fascinating evolutionary adaptations, especially when it comes to reproduction.

Take, for instance, the Arctic gentian (Gentianodes algida). This lovely plant can be found growing in alpine and tundra habitats in both North America and Asia. Like most plants of these habitats, the Arctic gentian has a low growth habit, forming a dense cluster of fleshy, narrow leaves that hug the ground. This protects the plant from blustering winds and extreme cold. From late July until early September, when the short growing season is nearly over, this wonderful plant comes into bloom. 

Clusters of white and blue speckled flowers are borne on short stems and, unlike other angiosperms that readily self-pollinate under harsh conditions, the Arctic gentian requires outcrossing to set seed. This can be troublesome. As you can imagine, pollinators can be in short supply in these habitats. What's more, with conditions changing on a dime, the flowers must be able to cope with whatever comes their way. The Arctic gentian is not helpless though. It has an interesting adaptation to these habitats and it involves movement.

Only a handful of plant species are known for their ability to move their various organs with relative rapidity. This gentian probably doesn't make that list very often. However, it probably should as its flowers are capable of responding to changes in weather by closing up shop. It is not alone in this behavior. Plenty of plant species will close their flowers on cold, dreary days. What is so special about the Arctic gentian is that it seems especially attuned to the weather. Within minutes of an incoming thunderstorm (a daily occurrence in the Rockies, for example) the Arctic gentian will close up its flowers. This is done via changes in turgor pressure within the cells. But what is the signal that cues this gentian in that a storm is fast approaching?

Researchers have investigated multiple stimuli in search of the answer. Plants don't seem to respond to changes in sunlight, wind, or humidity. Instead, temperature seemed to be the only signal capable of eliciting this response. When temperatures suddenly drop, the flowers will begin to close. Only when the temperature begins to rise will the flowers reopen. These movements are quite rapid too. Flowers will close completely within 6 - 10 minutes of a rapid decease in temperature. The reverse takes a bit longer, with most flowers needing 25 - 40 minutes to reopen.

So, why does the plant go through the trouble of closing up shop? It all has to do with sexual reproduction in these harsh conditions. Because this species doesn't self, pollen is at a premium. The plant simply can't afford the risk of rain washing it all away. The tightly closed flowers prevent that from happening. Also, wet flowers have been shown to discourage pollinators, even when favorable weather returns. Aside from interfering with pollen, rain also dilutes nectar, reducing its energy content and thus reducing the reward for any bee that would potentially visit the flower.

Being able to rapidly respond in changes in weather is important in these volatile habitats. Plants must be able to cope otherwise they risk extirpation. By closing up its flowers during inclement weather, the Arctic gentian is able to protect its vital reproductive resources.

Photo Credits: [1]

Further Reading: [1]

 

The Sterile Flowers of Hydrangea

Flowers are essentially billboards. They are saying to potential pollinators "hey, I'm full of energy-rich food and totally worth visiting." However, flowers are costly to produce and maintain. Reproduction isn't cheap, which has led some plants to take a more cost effective rout. In the genus Hydrangea, this means producing large, showy sterile flowers that draw attention to their smaller, less gaudy fertile flowers. 

These sterile flowers are technically colored up sepals. They don't produce reproductive structures or pollen. They are simply calling cards to insects that food is nearby. In the wild, Hydrangeas produce relatively few of these sterile flowers. Apparently it doesn't take much to draw insects in. The horticultural trade has shifted this balance to an obscene degree. When you look at a cultivated Hydrangea with its giant pom-pom looking corymb you are looking at a sterile structure that offers little if anything for pollinators. 

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This is a shame really because wild Hydrangeas are quite a boon for insects. Everything from beetles to bees visit their flowers. From the moment they open until the last one is fertilized, these shrubs are buzzing with activity. If you have the choice of a native Hydrangea over a cultivar, consider planting the native instead. You and you local pollinators will be happy you did. Here in North America there are at least four to choose from - the smooth Hydrangea (Hydrangea arborescens), the ashy Hydrangea (Hydrangea cinerea), the oakleaf Hydrangea (Hydrangea quercifolia), and the silverleaf Hydrangea (Hydrangea radiata). All of these occur east of the Mississippi and are largely denizens of the southeast. 

Further Reading: [1]

A Unique Case of Floral Mimicry

Pollination is one of the major advantages flowering plants have over the rest of the botanical tree. With a few exceptions, flowers have cornered this market. It no doubt has played a significant role in their rise to dominance on the landscape. The importance of flowers is highlighted by the fact that they are costly structures. Because they don't photosynthesize, all plants take a hit on energy reserves when it comes time to flower. Sepals, petals, pollen, nectar, all of these take a lot of energy to produce which is why some plants cheat the system a bit. 

Sexual mimicry is one form of ruse that has evolved repeatedly. The flowers of such tricksters mimic receptive female insects waiting for a mate. The evolution of such a strategy taps into something far deeper in the mind of animals than food. It taps into the need to reproduce and that is one need animals don't readily forego. As such, sexually deceptive flowers usually do away with the production of costly substances such as nectar. They simply don't need it to attract their pollinators. 

By and large, the world of sexual mimicry in plants is one played out mainly by orchids. However, there exists an interesting exception to this rule. A daisy that goes by the scientific name Gorteria diffusa has evolved a sexually deceptive floral strategy of its own. Native to South Africa, this daisy is at home in its Mediterranean climate. It produces stunning orange flowers that very much look like those of a daisy. On certain petals of the ray florets, one will notice peculiar black spots. From region to region there seems to be a lot of variation in the expression of these spots but all are textured thanks to a complex of different cell types. 

The spots may seem like random patterns until the flowers are visited by their pollinator - a tiny bee-fly known scientifically as Megapalpus nitidus. With flies present, one can sort of see a resemblance. This would not be a mistake on the observers part. Indeed, when researchers removed or altered these spots, bee-fly visitation significantly decreased. Although this didn't seem to influence seed production, it nonetheless suggests that those spots are there for the flies. 

When researchers painted spots on to non-textured petals, the bee-flies ignored those as well. It appears that the texture of the spots makes a big difference to visiting flies. What's more, although female flies visited the flowers, a majority of the visits were by males. It appears that the presence of these spots is keying in on the mate-seeking and aggregation behavior of their bee-fly pollinators. Further investigation has revealed that the spots even reflect the same kind of UV light as the flies themselves, making the ruse all the more accurate. This case of sexual mimicry is unique among this family. No other member of the family Asteraceae exhibits such reproductive traits (that we know of). Although it doesn't seem like seed production is pollinator limited, it certainly increases the chance of cross pollination with unrelated individuals.

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

Further Reading: [1] [2]

Who Pollinates the Flame Azalea?

By and large, one of the most endearing aspects of doing research in Southern Appalachia are the myriad Ericaceous species you inevitably encounter. Throughout the growing season, their flowers paint the mountainsides in a symphony of color. One of my favorite species to encounter is the flame azalea (Rhododendron calendulaceum).

This shrubby spectacle is a common occurrence where I work and its flowers, which range from bright yellows to deep orange and even red, put on a show that lasts a couple of weeks. It's not just me who enjoys the flowers either. Countless insects can be seen flitting to and from each blossom, sucking up rich reserves of nectar and pollen. It is interesting to watch a bee visit these flowers. Their outlandishly long anthers and style seem to be mostly out of reach for these smaller pollinators.

Bees attempting to grab some pollen look outlandishly clumsy in their attempts. What's more, small insects only seem to be able to get either nectar or pollen on any given visit. Rarely if ever do they make contact with the right floral parts that would result in effective pollination. Indeed, I am not the only person to have noticed this. Despite being visited by a wide array of insect species, only large butterflies seem capable to pollinating the flame azaleas stunning blooms.

The mechanism by which this happens is quite interesting. The reason small insects do not effectively pollinate these flowers has to do with the position of the anthers and style. Sticking far out from the center of the flower, they are too widely spaced to be contacted by small insect visitors. Instead, the only insects capable to transferring pollen from anthers to stigma are large butterflies. What is most strange about this relationship is that it all hinges on the size of the butterflies wings.

Only two species of butterfly, the eastern tiger swallowtail and the orange spangled fritillary, were observed to possess the right wing size and placement to achieve effective pollination for the flame azalea (though I suspect other larger species do so as well). This is quite unique as this is the only report of wing-mediated pollen transfer in northern temperate regions. The research team that discovered this noted that pollen transfer was greatest with the eastern tiger swallowtail, which is a voracious nectar hunter during the summer months.

Despite their popularity in pollinator gardens, butterflies are often considered poor pollinators. That being said, pollen transfer via wing surfaces has been a largely overlooked mechanism of pollination. Coupled with a handful of reports from tropical regions, this recent finding suggests that we must take a closer look at plant pollinator interactions, especially for plants that produce flowers with highly exerted anthers and stigmas. As the authors of the study put it, "transfer of pollen by butterfly wings may not be a rare event."

Photo Credit: [1]

Further Reading: [1]

A Beautiful and Bizarre Gentian

There is something about gentians that I am drawn to. I can't quite put my finger on it but it definitely has something to do with their interesting pollination strategies. One of the coolest gentian species I have ever met grows in the mountainous regions of western North America.

Meet Frasera speciosa a.k.a. the monument plant (a.k.a. elkweed). It is only one of 14 species in the genus. This fascinating species (as well as its relatives) lives out most of its life as a rosette of large, floppy leaves. The monument plant is what is known as a "monocarpic perennial", meaning it lives for many years as a rosette before flowering once and dying. It has been recorded that some individuals can be upwards of 30 years old by the time they flower!

This reproductive strategy brings with it a specific set of challenges but yet, if balanced correctly, offers many advantages. For starters, if you only flower once in a life time, you best make it count. The good news is, if flowering events are rare and widely spaced, this is a good strategy for avoiding herbivores. Such an irregular reproductive lifestyle means that the likelihood of a flowering population getting munched on is greatly reduced.

The same goes for seeds. If setting seed is a rare and widely spaced event, the likelihood of seed predation is also reduced. This is what is known as predator avoidance behavior. While it is not quite understood how plants synchronize flowering (though environmental conditions do play a role), it has been found that, for at least some populations, it alternates in intervals of 3 and 7 years. In essence, each flowering event can be seen as mast event. This keeps the overall impact of any potential herbivores and seed predators to a minimum.

This synchronous flowering strategy can also be beneficial for insuring cross pollination. The flowers are large and seemingly quite attractive to many different species of pollinators. By flowering all at once, a population is offering a tempting bonanza for pollinators that ensures many visits to each flower, thus increasing the chances of reproductive success. Since each individual plant invests all of its collective energy into a single flowering event, more energy is allocated to producing flowers and seed than if it flowered year after year.

The interesting habits of this plant's lifestyle don't end there. Each plant is essentially a pretty awesome parent! It has been found that seeds that are buried under the decomposing remains of a parent plant not only germinate better but the resulting seedlings also have a much higher rate of survival. This is good news for two big reasons.

For one, the decomposing remains enrich the surrounding soil while also creating a humid micro climate that is very conducive to growth. Second, the fact that they all germinate and grow relatively close to the parent plant, means that the density of young plants closely mimics that of the parental population. If the seeds were to be dispersed great distances from each other, it would be much more difficult to synchronize a flowering event and to ensure sufficient pollination. This way, entire populations grow up together in this nursery made from the remains of their parents. This is such a cool genus and I hope you get the chance to meet one for yourself.

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

Mighty Magnolias

Magnolias are one of those trees that even the non-botanically minded among us will easily recognize. They are one of the more popular plant groups grown as ornamentals and their symbolism throughout human history is quite interesting. But, for all this attention, few may realize how special magnolias really are. Did you know they they are one of the most ancient flowering plant lineages in existence?

Magnolias first came on to the scene somewhere around 95 million years ago. Although they are not representative of what the earliest flowering plants may have looked like, they do offer us some interesting insights into the evolution of flowers. To start with, the flower bud is enclosed in bracts (modified leaves) instead of more differentiated sepals. The "petals" themselves are not actually petals but tepals, which are also undifferentiated. The most striking aspect of magnolia flower morphology is in the actual reproductive structures themselves.

Magnolias evolved before there were bees. Because of this, the basic structure that makes them unique was in place long before bees could work as a selective pressure in pollination. Beetles are the real pollinators of magnolia flowers. The flowers have a hardened carpel to avoid damage by their gnawing mandibles as the feed. The beetles are after the protein-rich pollen. Because the beetles are interesting in pollen and pollen alone, the flowers mature in a way that ensures cross pollination. The male parts mature first and offer said pollen. The female parts of the flower are second to mature. They produce no reward for the beetles but are instead believed to mimic the male parts, ensuring that the beetles will spend some time exploring and thus effectively pollinating the flowers.

It is pretty neat to think that you don't necessarily have to track down a dawn redwood or a gingko to see a plant that has survived major extinction events. You can find magnolias very close to home with a keen eye. Looking at one, knowing that this is a piece of biology that has worked for millennia, is quite astounding in my opinion.

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

The Fetid Adderstongue

"Fetid adderstongue" seems like a pretty ominous name for such a small and beautiful plant. Hailing from coastal North America, the genus Scoliopus is most at home in the deep shaded forests of California and Oregon. Spring is the best time to see these little lilies and once you know a little bit about their ecology, such encounters are made all the more interesting.

There are two species nestled within this genus - S. bigelovii and S. hallii. Both are similar in that they are plants of deep shaded environments, however, you are more likely to find S. hallii growing along the banks of wooded streams. As is typical of many members of the lily family, their flowers are quite beautiful in appearance. The trick is finding them. Though showy, they are rather small and their dark coloration causes them to blend in well in their shaded environments. That is all fine and dandy for a species that relies more on smell rather than looks to attract pollinators.

As the common name suggests, the flowers of the fetid adderstongues give off a bit of an odor. I have heard it best described as "musty." The flowers of these two species attract a lot of fungus gnats. Although these tiny flies are generally viewed as sub par pollinators for most flowering plants, the fetid adderstongues seem to do well with them. What they lack in robust pollination behavior, they make up for in sheer numbers. There are a lot of fungus gnats hanging around wet, shaded forests.

The flowers themselves are borne on tall stalks. Though they look separate, they are actually an extension of a large, underground umbel. Once pollination has been achieved, the flower stalks begin to bend over, putting the developing ovaries much closer to the ground. Each seed comes equip with a fleshy little attachment called an eliasome. These are essentially ant bait. Once mature, the seeds are released near the base of the parent. Hungry ants that are out foraging find the fleshy attachment much to their liking.

They bring the seeds back to the nest, remove the eliasomes, and discard the seed into a trash midden. Inside the ant nest, seeds are well protected, surrounded by nutrient-rich compost, and as some evidence is starting to suggest, guarded against damaging fungal invaders. In other words, the plants have tricked ants into planting their seeds for them. This is a very successful strategy that is adopted by many different plant species the world over.

Though small, the fetid adderstongues are two plants with a lot of character. They are definitely a group that you want to keep an eye out for the next time you find yourself in the forests of western North America. If you do end up finding some, just take some time to think of all the interesting ecological interactions these small lilies maintain.

Photo Credits: [1] [2]

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

Red Nectar

No, your eyes are not playing tricks on you. This flower produces red nectar. Known scientifically as Nescodon mauritianus, this member of the bellflower family (Campanulaceae) grows only on the island of Mauritius. Although it is not alone in producing colored nectar (at least 60 other plant species do so as well) the striking contrast of the red nectar against the blue corolla had botanists wondering what exactly these plants are attracting.

Of course, the obvious answer were birds. It is no mystery that birds see in color much in the same way as us humans. However, multiple tests and observations demonstrated that birds were not the best pollinators for these flowers. In fact, the birds functioned mainly as thieves, stealing nectar without actually coming into contact with any of the necessary floral parts. The same thing happened to a Mauritian relative of the mallows named Trochetia blackburniana, which also produces colored nectar. 

To better understand the signalling mechanisms of these flowers, a team of researchers utilized a series of floral models. By filling the models with different colored nectar, they were able to better understand what they are attracting. As it turns out, the answer to this mystery are geckos. 

Phelsuma geckos visiting the flowers of  Trochetia blackburniana  (left) and flower models (right). Hansen et al. 2006

Phelsuma geckos visiting the flowers of Trochetia blackburniana (left) and flower models (right). Hansen et al. 2006

Living alongside these plants is a genus of day gecko called Phelsuma. They are endemic to Mauritius and can frequently be found visiting nectar-producing flowers in search of energy-rich nectar. By observing how the geckos responded to various color combinations, the team was able to discover that these geckos seem to prefer red and yellow nectar over clear. What's more, their feeding habits once inside the flower puts them in direct contact with the anthers and the stigma. Thus, the geckos function as the most effective pollinators for these plants. 

The team now feels that the colored nectar of these species serves as an honest reward for pollinating geckos. It is a stark indication that a reward is present. It is possible that because these geckos rely on brightly colored markings when interacting with each other, the selection for brightly colored floral signals has been favored in the evolution of these gecko pollinated plants. More work needs to be done to say for certain. What we do know for sure is that these day geckos are important pollinators in Mauritian ecosystems.

Photo Credits: [1] [2]

Further Reading: [1]

 

The Plant That Grows a Perch

For flowering plants, entering into an evolutionary relationship with birds as pollinators can be a costly endeavor. It can take a lot of energy to coax birds to their blossoms. On the whole, bird pollinated flowers are generally larger, sturdier, and produce more nectar. They tend to invest heavily in pigmentation. The plants themselves are often more robust as well. Unlike hummingbirds, which usually hover as they feed, other nectar-feeding birds require a perch. Often this is simply a stout branch or a stem, however, a plant endemic to South Africa takes bird perches to a whole new level - it grows one. 

Meet the rat's tail (Babiana ringens). Though not readily apparent, this bizarre looking plant is a member of the iris family. It is endemic to the Cape Province of South Africa where it can be found growing in sandy soils. It produces a fan of erect, grass-like leaves and, when conditions are right, a side branch full of red tubular flowers. This is when things get a bit strange. 

From that flowering stalk emerges a much longer stalk that is said to resemble the tail of a rat, earning this plant its common name. This stalk rises well above the rest of the flowers. If you look closely at the tip of this stalk you will quickly realize this is yet another flower stalk, though this one is sterile. Such a stalk may seem like a strange structure for this plant to produce until you consider its pollinators. 

The rat's tail has entered into an evolutionary relationship with a species of bird known as the malachite sunbird (Nectarina femosa). To access the nectar within, the malachite sunbird can't simply walk up to and shove its face down into the flowers. Instead, it must access them from above. To do so, it perches itself on the rigid sterile flower stalk. Once in position, the malachite sunbird can dip its long, down-curved beak directly into the flowers. This is exactly what the plant requires. In this perched position, pollen is brushed all over its chest. 

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Researchers wanted to know how obligate this relationship really was. By removing the perch on selected plants, they were able to demonstrate a reduction in pollination success . Specifically, male sunbirds were less likely to visit plants without the perch stalk. Although these plants are capable of self pollinating, like any sexually reproducing organism, outcrossing is the key to success. By offering the birds a sturdy perch allowing them exclusive access to their nectar, the plants guarantee sunbird fidelity.  

Photo Credits: [1] [2]

Further Reading: [1]