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] 

Understanding the Cocklebur

Spend enough time in disturbed areas and you will certainly cross paths with a cocklebur (Xanthium strumarium). As anyone with a dog can tell you, this plant has no problems getting around. It is such a common occurrence in my life that I honestly never stopped long enough to think about its place on the taxonomic tree. I always assumed it was some sort of Amaranth relative. You can imagine my surprise then when I recently learned that this hardy species is actually a member of the family Asteraceae. 

Cocklebur doesn't seem to fit with most of its composite relatives. For starters, its flowers are not all clustered together into a single flower head. Instead, male and female flowers are borne separately on the same plant. Male flower clusters are produced at the top of the flowering stem. Being wind pollinated, they quickly dump mass quantities of pollen into the air and wither away. The female flowers are clustered lower on the stem and consist of two pistillate florets situated atop a cluster of spiny bracts. 

After fertilization, these bracts swell to form the burs that so many of us have had to dig out of the fur of our loved ones. Inside that bur resides the seeds. Cocklebur is a bit strange in the seed department as well. Instead of producing multiple seeds complete with hairy parachutes, the cocklebur produces two relatively large seeds within each bur. There is a "top" seed, which sits along the curved, convex side of the bur, and a "bottom" seed that sits along the inner flat surface of the bur. Studies performed over a century ago demonstrated that these two seeds are quite important in maintaining cocklebur on the landscape. 

You see, cocklebur is an annual. It only has one season to germinate, grow, flower, and produce the next generation. We often think of annual plants as being quite hardy but in reality, they can sometimes be a bit picky about when and where they will grow. For that reason, seed banking is super important. Not every year will produce favorable conditions so dormant seeds lying in the soil act as an insurance policy. 

Whereas the bottom seed germinates within a year and maintains the plants presence when times are good, the top seed appears to have a much longer dormancy period. These long-lived seeds can sit in the soil for decades before they decide to germinate. Before humans, when disturbance regimes were a lot less hectic, this strategy likely assured that cocklebur would manage to stick around in any given area for the long term. Whereas fast germinating seeds might have been killed off, the seeds within the seed bank could pop up whenever favorable conditions finally presented themselves. 

Today cocklebur seems to be over-insured. It is a common weed anywhere soil disturbance produces bare soils with poor drainage. The plant seems equally at home growing along scoured stream banks as it does roadsides and farm fields. It is an incredibly plastic species, tuning its growth habit to best fit whatever conditions come its way. As a result, numerous subspecies, varieties, and types have been described over the years but most are not recognized in any serious fashion. 

Sadly, cocklebur can become the villain as its burs get hopelessly tangled in hair and fur. Also, every part of the plant is extremely toxic to mammals. This plant has caused many a death in both livestock and humans. It is an ironic situation to consider that we are so good at creating the exact kind of conditions needed for this species to thrive. Love it or hate it, it is a plant worth some respect. 

Photo Credits: [1] [2] 

Further Reading: [1] [2]

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

https://www.facebook.com/ampacityband

Caliochory - A Freshly Coined Form of Seed Dispersal

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A new form of seed dispersal has been described. It involves birds but not in the sense we traditionally think. Everyone understands how effectively birds disperse seeds contained in small fruits such as berries, or as barbs attached to their feathers. It took finding an out-of-place patch of Japanese stiltgrass (Microstegium vimineum) for lead author Dr. Robert Warren to start looking at bird dispersal in a different light. 

While working in his yard, he noticed a patch of Japanese stiltgrass growing out of a window planter some 6 feet off the ground. Japanese stiltgrass can be highly invasive but its seeds aren't adapted for vertical dispersal. However, it does employ a mixed mating system composed of outcrossing flowers at the tips of the spikes along with cleistogamous flowers whose seeds remain on the stem. Taking out a ladder, Warren discovered that the grass was growing out of a bird nest. It would appear that stiltgrass stems containing seeds were incorporated into the nest as building material and then germinated the following year. Thus began a deeper investigation into the realm of nest seeds.

Teaming up with researchers at Yale and the United States Forest Service, they set out to determine how often seeds are contained within bird nests. They collected nests from 23 different bird species and spread them over seed trays. After ruling out seeds from potential contamination sources (feces, wind, etc.), they irrigated the nests to see what would germinate. The results are quite remarkable to say the least.

Over 2,000 plants, hailing from 37 plant families successfully germinated. In total, 144 different plant species grew from these germination trials. The seeds appeared to be coming in from the various plant materials as well as the mud used to build these nests. What's more, nearly half of the seeds they found came from cleistogamous sources. Birds whose nests contained the highest amounts of seeds were the American robbin (Turdus migratorius) and the eastern bluebird (Sialia sialis). These results have led the authors to coin the term "caliochory," 'calio' being Greek for nest and 'chory' being Greek for spread.

It has long been assumed that cleistogamous reproduction kept seeds in the immediate area of the parent plant. This evidence suggests that it might actually be farther reaching than we presumed. What's more, these numbers certainly hint that this otherwise unreported method of seed dispersal may be far more common than we ever realized. Whether or not plants have evolved in response to such dispersal methods remains to be tested. Still, considering the diversity of birds, their nesting habits, and the availability of various plant materials, these findings are quite remarkable!

Photo Credits: [1]

Further Reading: [1]

On Dams & Storm Surges

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What would you say if I told you there was a connection between dams and the damage coastal communities are faced with after a storm surge? It may not seem obvious at first but as you will see, plants form a major connection between the two. Now more than ever, our species is dealing with the collective actions of the last few generations. Rare storm events are becoming more and more of a certainty as we head deeper into a future wrought with man-made climate change. The reality of this will only become more apparent for those smart enough to listen. Rivers are complex ecosystems that, like anything else in nature, are dynamic. Changes upstream will manifest themselves in a multitude of ways further downstream.

The idea of a dam is maddeningly brilliant. Much like our cells utilize chemical concentration gradients to produce biological power, we have converged on a similar solution to generate the electricity that powers our modern lives. A wall is built to block a waterway and store massive quantities of water on one side. That water is then forced through a channel where it turns turbines, which generate power. The problem is that the reservoir created to store all of that water drowns out ecosystems and the organisms that rely upon them (including humans). 

 

Here in the United States, we got a little dam crazy in the last few decades. With an estimated 75,000 dams in this country, many of which are obsolete, these structures have had an immense impact. One major issue with dams is the sediment load. As erosion occurs upstream, all of the debris that would normally be washed downstream gets caught behind the dam. Far from merely an engineering issue, a dams nature to trap sediment has some serious ecological impacts as well. 

Until humans came along, all major rivers eventually made their way to the coast. A free flowing river continually brings sediments from far inland, down to the mouth where they build up to form the foundation of coastal wetlands. Vegetation such as sedges, grasses, and mangroves readily take root in these nutrient-rich sediments, creating an amazingly rich and productive ecosystem. Less apparent, however, is the fact that these wetlands provide physical protection.

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Storm surges caused by storms like hurricanes can send tons upon tons of water barreling towards the coast. In places where healthy wetland vegetation is present, these surges are absorbed and much of that water never has a chance to hit the coast. In areas where these wetlands have vanished, there is nothing stopping the full brunt of the surge and we end up with a situation like we saw following Katrina or Sandy and are facing now with Harvey and Irma. Coastal wetlands provide the United States alone with roughly $23 billion in storm protection annually

These wetlands rely on this constant supply of sediment to keep them alive, both literally and figuratively. As anyone who has been to Florida can tell you, erosion is a powerful force that can eat away an entire coastline. Without constant input of sediment, there is nowhere for vegetation to grow and thus coastal wetlands are rapidly eroded away. This is where dams come in. An estimated 970,000 km (600,000 mi) of rivers dammed translates into a lot of sediment not reaching our coasts. The wetlands that rely on these sediments are being starved and are rapidly disappearing as a result. Add to that the fact that coastal developments take much of the rest and we are beginning to see a very bleak future for coastal communities both in the US and around the world. 

Photo Credit: [1] [2] [3]

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

In Search of a Parasitic Orchid

In this episode, In Defense of Plants goes looking for a tiny parasitic orchid called the autumn coralroot (Corallorhiza odontorhiza - http://bit.ly/2xQhzbc). It has no leaves and does not photosynthesize. Instead, it makes its living completely off of mycorrhizal fungi, digesting its hyphae within the cells of its highly derived roots. Along the way we meet plants such as:

 Music by: Artist: Ampacity

Track: Asimov's Sideburns

https://ampacity.bandcamp.com https://www.facebook.com/ampacityband

How Do Palms Survive Hurricanes?

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The destructive force of typhoons and hurricanes are no joking matter. Human structures are torn to shreds and flooded in the blink of an eye. It is devastating to say the least. With all of this destruction, one must wonder how native flora and fauna have coped with such forces over millions of years. The true survivors of these sorts of storms are the palms. What would completely shred an oak seems to ruffle a palm tree. What is it about palms that allows them to survive these storms intact? 

To better understand palm adaptations, one must first consider their place on the evolutionary tree. Palms are monocots and they have more in common with grasses than they do trees like oaks or pines. Their wood evolved independently of other tree species. Take a look at a palm stump. Instead of rings, you will see a dense structure of tiny straws that resemble the cross section of a telephone wire. This is because palms do not produce secondary xylem tissues that give other trees their rings. This makes them far more bendy than their dicotyledonous neighbors. Whereas the woods of oaks and maples are really good at supporting a lot of branch weight, it is considerably more rigid than that of palms. Palms forgo heavy branches for large leaves and therefore invest more in flexibility. The main stems of some palm species can bend as much as 40 to 50 degrees before snapping, a perfect adaptation to dealing with regular storm surges. 

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Another adaptation of the palms are their leaves. Unlike most trees, palms don't bother with spindly branches. Instead, they produce a canopy of large leaves supported by a flexible midrib. These act sort of like large feathers, allowing their canopy to readily shed water and bend against even the strongest winds. Although their leaves will snap if buffeted hard enough, palm canopies accrue considerably less damage under such conditions. Another adaptation exhibited by palm leaves is their ability to fold up like a paper fan. This reduces their otherwise large surface area against powerful winds. 

Finally, palms have rather dense roots. They sacrifice size for quantity. Instead of a few large roots anchored into the soil, palms produce a multitude of smaller roots that spread out into the upper layers of the soil. This is especially useful when growing in sand. By increasing the number of roots they put down, palms are able to hold on to a larger volume of soil and therefore possess a much heavier base. This keeps them stranding upright in all but the worst conditions. 

Of course, these are rather broad generalizations. Not all palms have evolved in response to such punishing weather events. Research has shown that such adaptations are more prevalent in palms growing in places like the Caribbean than they are in palms growing in the rainforests of South America. Regardless, their phylogenetic history has stood the test of time and will continue to do so for quite some time. 

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

Further Reading: [1] [2] 

Buffalo Grass, A Big Plant In A Small Package

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Grass identification is a bit challenging for me. However, there is one species I can always pick out of a crowd and for that, it holds a special place in my heart. My predilections aside, it is a fascinating species with an ecology worth getting to know a bit better. Today I would like to introduce you to the indomitable buffalo grass.

Known scientifically as Bouteloua dactyloides, this is one of the few dioecious grass species you can readily encounter here in North America. It is a denizen of the great planes and once thrived in the wake of disturbance left by massive herds of bison. Today you are more likely to encounter it growing alongside trails and other areas where taller vegetation is kept at bay. It is a hardy species and does exceptionally well in drought-prone soils. Like all warm season grasses, its photosynthetic machinery employs the C4 pathway, allowing buffalo grass to conserve moisture while ramping up photosynthesis during the hottest months of summer.

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Colonies of buffalo grass are stoloniferous, sending out creeping horizontal stems that will grow into new plants over time. Its small stature makes it easy to overlook. Flowering changes that. As mentioned above, buffalo grass is dioecious, which is kind of an odd trait for a grass. For the most part, male and female flowers exist on separate plants. Because pollen is wind dispersed, male flowers reach far above the leaves, ready to take advantage of the slightest breeze. Female plants present their flowers much closer to the ground, perhaps as a way of avoiding herbivory. Research has shown that, in any given population, monoecious plants are produced from time to time. It is thought that this might give buffalo grass a leg up when it comes to colonizing new habitats. If buffalo grass was strictly dioecious, both male and female seeds would have to find their way into a new habitat at the same time in order for a new population to establish. However, by producing monoecious seeds on occasion, the chances of being able to successfully reproduce in a new habitat increases.

Why this species has evolved to be dioecious is a bit of a mystery. Research on other dioecious plants suggest that it is a way of dealing with various environmental stresses such as competition and herbivory. Work on buffalo grass shows no significant bias towards males or females in any region. Most populations studied exhibit a 1:1 male to female ratio. Some plants seem to be able to switch over their lifetime, especially as it relates to new plants produced on stolons. Regardless of the selective pressures, buffalo grass seems to be doing quite well. Due to its small size and hardy disposition, many are looking towards buffalo grass as a great native lawn alternative. It doesn't require mowing and hot summer days don't seem to bug it. Couple that with its turf-like growth habit and you have yourself an excellent alternative to grasses like Kentucky bluegrass (Poa pratensis), which requires endless amount of water, fertilizer, and mowing to keep it up to our (dare I say) absurd standards.

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

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. Ladies and gentlemen, 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 quite 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. Each plant the birds then visit dusts off its own pollen while picking up pollen from previous 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]

Grasses That Feign Infestation

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Given the option, most of us would rather avoid a salad riddled with insects or an apple chock full of worms. Much as we prefer to avoid insect-infested fruits and vegetables, so too do many herbivores. Some plants seem to be taking advantage of this. In response to strong herbivore pressure, some plant species have evolved insect mimicry. One such case involves grass and aphids. 

Paspalum paspaloides can be found growing in tropical regions around the globe. In many ways they are similar to other C4 grasses. When they flower, however, one may notice something interesting. All of the flowers appear to be covered in aphids. Close inspection would reveal that this is not the case. Those clusters of dark specks swaying the breeze are simply the numerous dark anthers of the inflorescence. This has led some to hypothesize that these plants may be mimicking an aphid infestation.

This observation begs the question: "what benefit is there in mimicking aphids?" There are two major hypotheses that have been proposed in order to explain this phenomenon. The first is defense against herbivory. As stated above, herbivores often avoid plant material that has been infested with insects. Aside from any potential palatability issues, large populations of insect pests can signal a decrease in the nutritional value of a potential food source. Why waste time eating something that is already being eaten? Evidence in support of this hypothesis has come from other systems. A wide array of herbivores, both mammalian and insect, have been shown to avoid aphid-infested plant material.

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The second hypothesis is one of avoiding future infestations. Aphids are clonal organisms with a short generation time. It does not take long for a few aphids to become many, and many to become an infestation. As such, aphids looking for a new plant to colonize habitually avoid plants that already have aphids on them. It could very well be that such aphid mimicry is a means by which the grass keeps actual aphids at bay.

If this is a form of true mimicry then the question is not a matter of which hypothesis but the relative influence of each. It seems that it very well could be driven by a mixture of both strategies. Still, all of this is speculative until actual experiments are carried out. Those who originally put forth these ideas have identified similar potential mimicry systems in other plants as well. The idea is ripe for the testing!

Photo Credits: [1]

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

 

The Ginkophytes Welcome a New Member

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Despite their dominance on the landscape today, the evolutionary history of the major seed-bearing plant lineages is shrouded in mysteries. We simply don't have a complete picture of their evolution and diversification through time. Still, numerous fossils are turning up that are shedding light on some of these mysteries, including some amazingly well-preserved plant fossils from Mongolia. One set of fossils in particular is hinting that the part of the seed-bearing family tree that includes the Ginkgo was much more diverse in both members and forms.

The fossils in question were unearthed from the Tevshiin Govi Formation of Mongolia and date back to the Early Cretaceous period, some 100 to 125 million years ago. Although these fossils do not represent a newly discovered plant, their preservation is remarkable, allowing a much more complete understanding of what they were along with where they might sit on the family tree. The fossils themselves are lignified and have preserved, in extreme detail, fine-scale anatomical details that reveal their overall structure and function.

The paleobotanical team responsible for their discovery and analysis determined that these were in fact seed-bearing cupules of a long-extinct Ginkgophyte, which they have named Umaltolepis. Previous discoveries have alluded to this as well, however, their exact morphology in relation to the entire organism has not always been clear. These new discoveries have revealed that the cupules (seed-bearing organs) themselves were borne on a stalk that sat at the tips of short shoots, very similar to the shoots of modern Ginkgo. They opened along four distinct slits, giving the structure an umbrella-like appearance.

The seeds themselves were likely wind dispersed, however, it is not entirely clear how fertilization would have been achieved. Based on similar analyses, it is very likely that this species was wind pollinated. Alongside the cupules were exquisitely preserved leaves. They were long, flat, and exhibit venation and resin ducts similar to that of the extant Ginkgo biloba. Taken together, these lines of evidence point to the fact that this group, currently represented by a single living species, was far more diverse during this time period. The differences in seed bearing structures and leaf morphology demonstrates that the Ginkgophytes were experimenting with a wide variety of life history characteristics.

Records from across Asia show that this species and its relatives were once wide spread throughout the continent and likely inhabited a variety of habitat types. Umaltolepis in particular was a denizen of swampy habitats and shared its habitat with other gymnosperms such as ancient members of the families Pinaceae, Cupressaceae, and other archaic conifers. Because these swampy sediments preserved so much detail about this ecosystem, the team suggests that woody plant diversity was surprisingly low, having turned up fossil evidence for only 10 distinct species so far. Other non-seed plants from Tevshiin Govi include a filmy fern and a tiny moss, both of which were likely epiphytes.

Whereas this new Umaltolepis species represents just one player in the big picture of seed-plant evolution, it nonetheless a major step in our understanding of plant evolution. And, at the end of the day, fossil finds are always exciting. They allow us a window back in time that not only amazes but also helps us understand how and why life changes as it does. I look forward to more fossil discoveries like this.

 

*Thanks to Dr. Fabiany Herrera for his comments on this piece

Photo Credits: [1]

Further Reading: [1] [2]

Floral Mucilage

Spend enough time around various Bromeliads and you will undoubtedly notice that some species have a rather gooey inflorescence. Indeed, floral mucilage is a well documented phenomenon within this family, with something like 30 species known to exhibit this trait. It is an odd thing to experience to say the least.

The goo takes on an interesting consistency. It reminds me a bit of finding frog spawn as a kid. Their brightly colored flowers erupt from this gooey coating upon maturity and the seeds of some species actually develop within the slimy coating. Needless to say, the presence of mucilage in these genera has generated some attention. Why do these plants do this?

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Some have suggested that it is a type of reward for visiting pollinators. Analysis of the goo revealed that it is 99% water and 1% carbohydrate matrix with no detectable sugars or any other biologically useful compounds. As such, it probably doesn't do much in the way of attracting or rewarding flower visitors. Another hypothesis is that it could offer antimicrobial properties. Bromeliads are most often found in warm, humid climates where fungi and bacteria can really do a number. Again, no antimicrobial compounds were discovered nor did the mucilage show any sort of growth inhibition when placed in bacterial cultures.

It is far more likely that the mucilage offers protection from hungry herbivores. Flowers are everything to a flowering plant. They are, after all, the sexual organs. They take a lot of energy to produce and are often brightly colored, making them prime targets for a meal. Anything that protects the flowers during development would be a boon for any species. Indeed, it appears that the mucilage acts as a physical barrier, protecting the developing flowers and seeds. One study found that flowers protected by mucilage received significantly less damage from weevils than those without mucilage.

The mucilage could also provide another benefit to Bromeliads. Because these plants rely on water stored in the middle of their rosette (the tank, as it is sometimes called), some species may also gain a nutritional benefit as well. Bromeliad flowers emerge from this central tank so anything that gets stuck in the mucilage may eventually end up decomposing in the water. Since nutrients are absorbed along with the water, this could be an added meal for the plant. To date, this has not been confirmed. More work is needed before we can say for sure.

Photo Credit: [1] [2]

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

 

A Wonderful Hill Prairie

In this episode, we explore a hill prairie situated along the Middle Fork River. Hill prairies are essentially what the sound like but often grow in drought-prone soils.

In this episode we get up close and personal with:

Cylindrical Blazingstar (Liatris cylindracea)
https://link.springer.com/article/10.1007/s10531-016-1202-y

Prairie Dock (Silphium terebinthinaceum)
http://www.illinoiswildflowers.info/prairie/plantx/pr_dockx.htm

Whorled Milkwort (Polygala verticillata)
https://gobotany.newenglandwild.org/species/polygala/verticillata

Sideoats Grama (Bouteloua curtipendula)
http://www.illinoiswildflowers.info/grasses/plants/so_grama.htm


Producer, Writer, Creator, Host:
Matt Candeias (http://www.indefenseofplants.com)

Producer, Editor, Camera:
Grant Czadzeck (http://www.grantczadzeck.com)

_________________________________________________________________

Music by: 
Artist:Snowball II
Track: Hurry
https://snowballii.bandcamp.com/

Large Parrots And Their Influence On Amazonian Ecosystems

Parrots, especially the larger species, have long been thought to be a bane to plant reproduction. Anyone that has watched a parrot feed may understand why this has been the case. With their incredible beaks, parrots make short work of even the toughest seeds. However, this assumption is much too broad. In fact, recent research suggests that entire Amazonian ecosystems may have parrots to thank.

Bolivia's Amazonian savannas are remarkable and dynamic ecosystems. These seasonally flooded grasslands are dotted with forest islands dominated by the motacú palm (Attalea princeps). These forest patches are an integral part of the local ecology and have thus received a lot of attention both culturally and scientifically. The dominance of motacú palm poses an intriguing question - what maintains them on the landscape?

The fruits of this palm are quite large and fleshy. Some have hypothesized that this represents an anachronism of sorts, with the large fruit having once been dispersed by now extinct Pleistocene megafauna. Despite this assumption, these forest islands persist. What's more, motacú palms still manage to germinate. Obviously there was more to this story than meets the theoretical eye. As it turns out, macaws seem to be the missing piece of this ecological puzzle. 

Researchers found that three species of macaw (Ara ararauna, A. glaucogularis, and A. severus) comprised the main seed dispersers of this dominant palm species. What's more, they manage to do so over great distances. You see, the palms offer up vast quantities of fleshy fruits but not much in the way of a good perch on which to eat them. Parrots such as macaws cannot take an entire seed down in one gulp. They must manipulate it with their beak and feet in order to consume the flesh. To do this they need to find a perch.

Suitable perches aren't always in the immediate area so the macaws take to the wing along with their seedy meals. Researchers found that these three macaw species will fly upwards of 1,200 meters to perch and eat. Far from being the seed predators they were assumed to be, the birds are actually quite good for the seeds. The fleshy outer covering is consumed and the seed itself is discarded intact. This suggests that preferred perching trees become centers of palm propagation and they have the parrots to thank. 

Indeed, seedling motacú palms are frequently found within 1 - 5 meters of the nearest perching tree. No other seed disperser even came close to the macaws. What's more, introduced cattle (thought to mimic the seed dispersing capabilities of some extinct megafauna) had a markedly negative effect on palm seed germination thanks to issues such as soil compaction, trampling, and herbivory. Taken together, this paints a radically different picture of the forces structuring this unique Amazonian community.

Photo Credits: Wikimedia Commons

Further Reading: [1]

The Squirting Cucumber

Plants have gone to great lengths when it comes to seed dispersal. One of the most bizarre examples of this can be found in an ambling Mediterranean plant affectionately referred to as the squirting cucumber. As funny as this may sound, the name could not be more appropriate. 

Known scientifically as Ecballium elaterium, the squirting cucumber can be found growing along roadsides and other so-called "waste places" from the Mediterranean regions of western Europe and northern Africa all the way to parts of temperate Asia. It is the only member of its genus, which resides in the family Cucurbitaceae. It is a rather toxic species as well, with all parts of the plant producing a suite of chemicals called cucurbitacins. In total, it seems like a rather unassuming plant. It goes through the motions of growing and flowering throughout the summer months but the real show begins once its odd fruits have ripened. 

A cursory inspection would not reveal anything readily different about its fruit. Following fertilization, they gradually swell into modest sized version of the sorts you expect from this family of plants. It's what is going on within the fruit that is rather interesting. As the fruit reaches maturity, the tissues surrounding the seeds begin to break down. The breakdown of this material creates a lot of mucilaginous liquid, causing internal pressure to build. And I mean a lot of pressure. Measurements have revealed that at peak ripening, pressures within the fruit can reach upwards of 27 atm, which is 27 times the amount of atmospheric pressure we experience when standing at sea level!

A cross section of the fruit showing the weakened connection point.

A cross section of the fruit showing the weakened connection point.

At the same time, the attachment point of the stem or "peduncle" begins to weaken. With all that pressure building, it isn't long before something has to give. This is exactly the moment when the squirting cucumber earns its name. The stem breaks away from the fruit, revealing a small hole. Within a fraction of a second, all of that pressurized mucilage comes rocketing outward carrying the precious cargo of seeds with it. 

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The result is pretty remarkable. Seeds are launched anywhere from 6 to 20 feet (1 - 6 m) away from the parent plant. This form of dispersal falls under the category of ballistic seed dispersal and it is incredibly effective. Getting away from the competitive environment immediately surrounding your parents is the first step in the success of any plant. The squirting cucumber does just that. It is no wonder then that this is an incredibly successful plant species. 

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

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

Tropical Ferns in Temperate North America

All plants undergo some form of alternation of generations. It is the process in which, through reproduction, they cycle between a haploid gametophyte stage and a diploid sporophyte stage. In ferns and lycophytes, this alternation of generations has been taken to the extreme. Instead of the sporophyte relying on the gametophyte for sustenance, the two generations are physically independent and thus separated from one another. In a handful of fern genera here in North America, this has led to some intriguing and, dare I say, downright puzzling distributions. The presence of a small handful of tropical fern genera in temperate North America has generated multiple scientific investigations since the early 1900's. However, as is constantly happening in science, as soon as we answer one question, seemingly infinite more questions arise. At the very least, the presence of these ferns in temperate regions offers us a tantalizing window into this continents ancient past.

To say any of these ferns offer the casual observer much to look at would be a bit of an exaggeration. They do not play out their lives in typical fern fashion. These out of place tropical ferns exists entirely as asexual colonies of gametophytes, reproducing solely by tiny bundles of cells called gemmae. What's more, you will only find them tucked away in the damp, sheltered nooks and crannies of rocky overhangs and waterfalls. Buffered by unique microclimates, it is very likely that these fern species have existed in these far away corners for a very, very long time. The last time their respective habitats approached anything resembling a tropical climate was over 60 million years ago. Some have suggested that they have been able to hang on in their reduced form for unthinkable lengths of time in these sheltered habitats. Warm, wet air gets funneled into the crevices and canyons where they grow, protecting them from the deep freezes so common in these temperate regions. Others have suggested that their spores blew in from other regions around the world and, through chance, a few landed in the right spots for the persistence of their gametophyte stages.

The type of habitat you can expect to find these gametophytes.

Aside from their mysterious origins, there is also the matter of why we never find a mature sporophyte of any of these ferns. At least 4 species in North America are known to exist this way - Grammitis nimbata, Hymenophyllum tunbridgense, Vittaria appalachiana, and a member of the genus Trichomanes, most of which are restricted to a small region of southern Appalachia. In the early 1980's, an attempt at coaxing sporophyte production from V. appalachiana was made. Researchers at the University of Tennessee brought a few batches of gametophytes into cultivation. In the confines of the lab, under strictly controlled conditions, they were able to convince some of the gametophytes to produce sporophytes. As these tiny sporophytes developed, they were afforded a brief look at what this fern was all about. It confirmed earlier suspicions that it was indeed a member of the genus Vittaria, or as they are commonly known, the shoestring ferns. The closest living relative of this genus can be found growing in Florida, which hints at a more localized source for these odd gametophytes, however, both physiology and subsequent genetic analyses have revealed the Appalachian Vitarria to be a distinct species of its own. Thus, the mystery of its origin remains elusive.

In order to see them for yourself, you have to be willing to cram yourself into some interesting situations. They really put the emphasis on the "micro" part of the microclimate phenomenon. What's more, you really have to know what you are looking for. Finding gametophytes is rarely an easy task and when you consider the myriad other bryophytes and ferns they share their sheltered habitats with, picking them out of a lineup gets all the more tricky. Your best bet is to find someone that knows exactly where they are. Once you see them for the first time, locating other populations gets a bit easier. The casual observer may not understand the resulting excitement but once you know what you are looking at, it is kind of hard not to get some goosebumps. These gametophyte colonies are a truly bizarre and wonderful component of North American flora.

Photo Credit: [1] [2]

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

In Search of the Orange Fringed Orchid

In Defense of Plants is finally back for another exciting botanical adventure! This week we explore another wonderful sand prairie in search of one of North America's most stunning terrestrial orchids - the orange fringed orchid (Platanthera ciliaris). Along the way, we meet a handful of great native plant species that are at home in these sandy soils.

Music by: 
Artist: Eyes Behind the Veil
Track: Folding Chair
Album: Besides
https://eyesbehindtheveil.bandcamp.com/

Herbarium Biases

Humans carry countless biases with them wherever they go. Even the logical mind of a scientist is no stranger to prejudice. Identifying such biases in the way we do science is key to improving the discipline and, as computing power and access to big data increases, we are gaining a better understanding of just how prevalent our biases really are. A recent study that looked at herbarium collections around the world aims to do just that.

With herbaria closing shop around the globe, the need to digitize collections has never been more urgent. Although more and more collections are finding their way into digital libraries, a vast majority of herbarium collections risk being lost forever. This alone represents a major bias. Such organismal science has sadly been scoffed at in recent decades. Still, enough collections have been entered into databases that interesting patterns are starting to emerge. A team of researchers recently took a closer look at roughly 5 million digitized floras representing the most complete digital floras from Australia, South Africa, and New England.

In doing so, the team was able to find some startling biases in these collections. They broke them down into a handful of categories with the hope that botanists and ecologists can start to improve on these gaps over the coming decades. Although the floras they examined by no means represent anything close to a complete picture of our floristic understanding of the world, they nonetheless mirror issues that are sure to crop up no matter where collections have been made.

The first major category is that of spatial or geographic bias. This occurs whenever specimens are collected at a higher frequency in one place over another. There are likely many reasons for this - ease of access, proximity to research institutions, just to name a few. The team found that herbarium collections tended to occur in the same areas through time. What's more, they tended to occur more often near roads with a surprising 50% of specimens collected within 2 km of a roadside. This can result in a highly skewed perspective of the kind of taxa represented in a region. Roadside vegetation is comprised of species capable of dealing with runoff, soil compaction, and pollution, and is likely depauperate of taxa less able to handle such conditions. They also found a elevational bias, with a majority of specimens having been collected below 500 meters. 

Maps demonstration spatial biases in herbarium collections. Those in red have more collections and those in blue have fewer collections.

Maps demonstration spatial biases in herbarium collections. Those in red have more collections and those in blue have fewer collections.

The second major category is that of temporal bias. This occurs whenever specimens are collected more frequently during certain parts of the year over others. The team found that collections disproportionately occurred during spring and summer months. As anyone who hikes can tell you, there is a lot of variation among plant communities from season to season and any good collection should sample a location multiple times a year. In addition to seasonal biases, the team also found extreme biases in terms of history. Collections in South Africa and Australia started to rise shortly after World War II and peaked in the 1980's and 1990's respectively. Compare this to New England where peak collections occurred nearly 100 years prior. If we are to track long term trends and changes in the flora of various regions, collections need to occur far more regularly. Obviously institutions have shied away from such investigations in recent decades. Only public interest and funding can reverse such trends, hopefully not before it is too late.

The third major bias they found is that of trait bias. This occurs whenever a collector specifically aims for species with a certain life history characteristic (annual vs. perennial, woody vs. herbacious) as well as species of conservation concern. Indeed, the team found that perennial species were over-represented in most herbarium collections. Also, gramminoids dominated herbarium collections in Australia and South Africa whereas herbs and trees were over-represented in New England. Another interesting pattern that emerged is that short plants had higher representation in harbaria than taller species. Obviously this has a lot to do with ease of collection.

Another pattern that emerged which is of conservation concern is that threatened or endangered species are severely under-represented in herbarium collections. Although care must be taken to not over-collect species whose numbers are dwindling, their lack of representation in herbarium collections can seriously hinder conservation efforts. Such under-represenation can lead to erroneous estimations of species abundances and distributions. It can also hinder our understanding of plant community dynamics.

The fourth major bias is that of phylogenetic bias. Certain clades are more sought after than others. This leads to a disproportionate amount of showy or valuable species turning up in herbaria around the globe. It also leads to an over-representation of potentially "useful" plant species in terms of things like medicines or dyes. This leaves a large portion of regional floras under-sampled. This in turn exacerbates issues relating to our understanding of plant community dynamics and the change in plant abundance and distribution through time.

Finally, the fifth major bias is that of collector bias. This pattern stems from the fact that in all the regions sampled for this study, a majority of the collections were made by only a handful of individuals. This means that all of these collections are the products of the habits and preferences of these collectors. Some collectors may favor sampling the entire flora of a region whereas others may favor certain clades over others. Similarly, some collectors may favor plants with interesting physiologies whereas other may favor plants with peculiar life-histories such as carnivores or succulents.

The use and importance of herbaria has changed a lot over the last two centuries. Whereas they largely started out as a tool for taxonomists, the utility of herbarium collections has since expanded into areas that were never thought possible. With the advent of new technologies, who knows what the future holds. Of course, this means nothing if interest and support for herbarium collections continues to decline. Their utility in the context of research and conservation cannot be understated. We need herbaria now more than ever. Understanding biases is a great step towards improving the discipline. We must aim to improve collections in these so-called cold spots and to avoid as many biases as possible in doing so.

Photo Credits: Wikimedia Commons

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]