Caliochory - A Freshly Coined Form of Seed Dispersal

Photo by Ude licensed under CC BY-SA 3.0

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

Photo by JJ Harrison licensed under CC BY-SA 3.0

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.

Photo by HiGorgeous licensed under CC BY 3.0

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?

U.S. Navy photo by Jim Brooks public domain

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, such wood 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. 

Photo by Kadeve licensed under CC BY-SA 3.0

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. 

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

Further Reading: [1] [2] 

Buffalo Grass, A Big Plant In A Small Package

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.

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.

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

Photo by Forest & Kim Starr licensed under CC BY 3.0

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.

Photo by Mokkie licensed under CC BY-SA 3.0

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]

The Ginkophytes Welcome a New Member

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.

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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.

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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.

LISTEN TO EP 300 OF THE IN DEFENSE OF PLANTS PODCAST TO LEARN MORE ABOUT THIS DISCOVERY AND MORE!

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

Photo Credits: [1]

Further Reading: [1] [2]

Floral Mucilage

Photo taken in Monteverde, Costa Rica. Author: Cody Hinchliff, 2004. Licensed under CC BY-SA 3.0

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?

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]

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

Photo by I, Luc Viatour licensed under CC BY 2.0

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]

Tropical Ferns in Temperate North America

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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 North America’s 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.

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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 Vittaria to be a distinct species of its own. Thus, the mystery of its origin remains elusive.

[SOURCE]

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. Also, 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/

Closed on Account of Weather

Photo by Alpsdake licensed under CC BY-SA 3.0

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]

Meet The Compass Plant

Few prairie plants stand out more than the compass plant (Silphium laciniatum). With its uniquely lobed leaves and a flower stalk that rises well above the rest of the vegetation, it is nearly impossible to miss. It is also quite easy to identify. Seeing a population in full bloom is truly a sight to behold but the ecology of this species makes appreciating its splendor all the more enjoyable. Today I would like to introduce you to this wonderful member of the aster family.

Any discussion about this species inevitably turns to its common name. Why compass plant? It all has to do with those lovely lobed leaves. When they first develop, the leaves of the compass plant are arranged randomly. However, within 2 to 3 weeks, the leaves will orient themselves so that their flat surfaces face east and west. They also stand vertically. This is such a reliable feature of the plant that past generations have learned to use it as a reliable way in which to orient themselves.

Photo by peganum licensed under CC BY-SA 2.0

Of course, helping humans find their way is not why this feature evolved. The answer to their orientation has to do with surviving in the open habitats in which they grow. Anyone who has ever spent time hiking around in prairie-like habitats will tell you that the sun can be punishing and temperatures get hot. What's more, the range of this species overlaps with much of the rain shadow produced by the Rocky Mountains meaning water can often be in short supply.

By orienting their leaves in a vertical position with the flat surfaces face east and west, the plants are able to maximize their carbon gain as well as their water use efficiency. At the same time, the vertical orientation limits the amount of direct solar radiation hitting the leaf. In essence, compass plant leaf orientation has evolved in response to the stresses of their environment. Research has shown that the sun's position in early morning is the stimulus that the plant cues in on during leaf growth.

Aside from its fascinating biology, the compass plant is also ecologically important. Myriad pollinators visit its large composite flowers and many different species of birds feed on their seeds. However, it is the insect community supported by the compass plant that is most impressive. Surveys have shown that nearly 80 different species of insect can be found living on or in it stems. Many of these are gall making wasps and their respective parasitoids. With individual plants producing up to 12 stems each, these numbers soon become overwhelming. Needless to say, this is one of the cornerstone plant species anywhere it grows naturally.

Photo Credit: [1]

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

An Orchid of Hybrid Origin

Hybridization is an often overlooked mechanism for evolution. We are taught in high school that hybrids such as mules and ligers are one-off's, evolutionary dead ends doomed to a life of sterility. Certainly this holds true in many instances. Species separated by great lengths of time and space are simply incompatible. However, there are instances throughout the various kingdoms of life in which hybrids do turn out viable.

If they are different enough from either parent, their creation may lead to speciation down the line. Such events have been found in ferns, butterflies, and even birds. One particular example of a hybrid species only recently came to my attention. While touring the Atlanta Botanical Garden I came across a fenced off bed of plants. Inside the fence were orchids standing about knee height. At the top of each plant was a brilliant spike of orange flowers. "Ah," I exclaimed, "the orange fringed orchid!" The reply I got was unexpected - "Sort of."

What I had stumbled across was neither the orange fringed orchid (Platanthera ciliaris) nor the crested yellow orchid (Platanthera cristata). What I was looking at were a small handful of the globally imperiled Chapman's fringed orchid (Platanthera chapmanii). Though there is some debate about the origins of this species, many believe it to be a naturally occurring hybrid of the other two. In many ways it is a perfect intermediate. Despite its possible hybrid origins, it nonetheless produces viable seed. What's more, it readily hybridizes with both parental species as well as a handful of other Platanthera with which it sometimes shares habitat.

Despite occasionally being found along wet roadside ditches, this species is rapidly losing ground. The wet meadows and pine savannas it prefers are all too quickly being leveled for housing and other forms of development. Although it once ranged from southeast Texas to northern Florida, and southeast Georgia, it has since been reduced to less than 1000 individuals scattered among these three states.

There is a light at the end of the tunnel though. Many efforts are being put forth to protect and conserve this lovely orchid. Greenhouse propagation in places like the Atlanta Botanical Garden are helping supplement wild populations while at the same time, maintaining genetic diversity. New populations have been located in Georgia and are now under protection. Though not out of the woods yet, this species serves as a reminder that a little bit of effort can go a long way.

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

How Plants Perceive Light

For all but a handful of plants, sunlight is vital to their existence. It provides the energy needed to break molecules of CO2 and water in order to synthesize carbohydrates. It is no wonder then that plants are incredibly attuned to their light environment. They grow towards it, they compete for it, they simply can't live without it. Exactly how plants (as well as many bacteria and even some fungi) perceive light is quite fascinating. It involves a small family of proteins called "phytochromes" whose chemical properties function like an on and off switch. Today I would like to briefly introduce you to this system. 

The activity of phytochrome proteins can be quite complex. In fact, many aspects of this system are still awaiting discovery. Still, we know pretty well how the phytochrome system functions with light and it all comes down to the color red. Pure sunlight is white light. It contains all of the wavelengths in the visible spectrum and then some. Phytochrome responds to two areas of this spectrum: red wavelengths of around 667 nm and far-red wavelengths around 730 nm. 

Photo by byr7 licensed under CC BY 2.0

This range of the spectrum is quite useful when it comes to assessing whether or not there is enough light for photosynthesis. Unfiltered sunlight contains the most red light. As sunlight passes through the leaves of the canopy or as the sun sets, the ratio of far-red light increases. Far-red light is not conducive to photosynthesis. As such, the long-term survival of photosynthetic organisms is tied to figuring out the relative abundance of red and far-red light. 

This is where the phytochrome system comes in. It comes in two forms - an active form and an inactive form. When the inactive form absorbs red wavelengths, it is converted to its active form. This is the form that signals to the plant that there is enough light for physiological activity. When the ratio of wavelengths hitting the active form becomes dominated by far-red wavelengths (as it does when a plant is shaded or when the sun sets), the phytochrome is converted back into its inactive form. This in turn signals the plant to shut down many of the physiological activities within.

The structure of phytochrome in its inactive form (left) and active form (right).

This on and off switch is how plants regulate everything from growth to flowering. The ratio of active to inactive forms can tell some plants what time of year it is. If there is more inactive form within its tissues, the plant "knows" that the days are growing shorter. Phytochrome is also involved in the number and the size of leaves that a plant will produce. Similarly, it is how plants know when they are being shaded out by their neighbors. The more neighboring plants there are, the more filtered the sunlight becomes and the ratio of far-red light increases. It is even involved in the process of seed germination. Small seeds that don't have enough food reserves (think lettuce seeds) will only germinate once their phytochrome is converted to its active form. In doing so, they ensure that they aren't germinating in an environment with too much shade or deep under the soil. 

Scientists are still working out exactly how the phytochrome system is able to regulate so many functions in plants. In some cases it can directly interact with molecules in the cytoplasm of plant cells. In other cases, it is transported into the nucleus where it can activate or deactivate particular genes. What we do know is that the phytochrome system is vitally important not just for the organisms that produce it, but for life as we know it. Without plants there could be no life on this planet.

Photo Credits: [1] [2]

Further Reading: [1] [2] [3] [4]

The Flowering Rush

Photo by Quite Adept licensed under CC BY-NC-ND 2.0

Say the words "flowering rush" and many will picture some grass-like, pond vegetation. However, the plant I am talking about today is not a rush at all. Known scientifically as Butomus umbellatus, the flowering rush superficially resembles a patch of true rushes, especially when not in flower. However, it is actually quite a unique species and the sole member of the family Butomaceae. Native to parts of Europe and Asia, this beautiful aquatic plant can now be found invading wetlands throughout northern North America.

Growing quite tall and producing an umbel of beautiful pink flowers, it is no wonder that this plant came to North America as a horticultural curiosity. Its overall appearance suggests a relationship with the genus Allium but genetic analysis puts it somewhere near the water plantains - Alismataceae. The interesting thing about this plant is that here in North America, individual populations exhibit either diploid or triploid chromosome counts.

Photo by Christian Fischer licensed under CC BY-SA 3.0

This is most likely a function of its horticultural past. Many commonly grown garden species have been selected for polyploidy in their chromosomes. Polyploid plants are often larger and more hardy than their diploid relatives, mostly due to the extra genetic material they harbor. It has been noted that there seems to be some reproductive differences between diploid and triploid flowering rush populations as a result. Diploids are more likely to reproduce sexually via seeds whereas triploids are usually sterile and reproduce vegetatively. Triploids are also less commonly found as escapees but they are more widely distributed than diploids. This is likely due to the fact that triploids are more commonly planted in gardens.

Whereas it seems that there is plenty of areas where people disagree on the invasive species issue, one thing we must keep in mind is that, no matter where you stand, biological invasions are one of the largest natural experiments this world has ever seen. We mustn't waste any opportunity to learn from these invasions and to gather as much data as we possibly can. Species like flowering rush offer us insights into how and why some species become invasive while others do not. The more we know, the better we can learn from the mistakes of the past.

Photo Credit: [1] [2]

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

Meet The Powder Gun Moss

I get very excited when I am able to identify a new moss. This is mainly due to the fact that moss ID is one of my weakest points. I was sitting down on a rock the other day taking a break from vegetation surveys when I looked to my right and saw something peculiar. The area was pretty sloped and there was some exposed soil in the vicinity. Covering some of that soil was what looked like green fuzz. Embedded in that fuzz were these strange green urns.

I busted out my hand lens and got a closer look. This was definitely a moss but one I had never seen before. The urns turned out to be capsules. Later, a bit of searching revealed this to be a species of moss in the genus Diphyscium. This genus is the largest within the family Diphysciaceae and here in North America, we have two representatives - D. foliosum and D. mucronifolium.

These peculiar mosses have earned themselves the common name 'powder gun moss.' The reason for this lies in those strange sessile capsules. Unlike other mosses that send their capsules up on long, hair-like seta in order to disperse their spores on the faintest of breezes, the Diphyscium capsules remain close to the ground. In lieu of wind, a powder gun moss uses rain. In much the same way puffball mushrooms harness the pounding of raindrops, so too do the capsules of the powder gun moss. Each raindrop that hits a capsule releases a cloud of spores that are ejected into an already humid environment full of germination potential.

Luckily for moss lovers like myself, the two species of Diphyscium here in North America tend to enjoy very different habitats. This makes a positive ID much more likely. D. foliosum prefers to grow on bare soils whereas D. mucronifolium prefers humid rock surfaces. Because of this distinction, I am quite certain the species I encountered is D. foliosum. And what a pleasant encounter it was. Like I said, it isn't often I accurately ID a moss so this genus now holds a special place in my mind.

Further Reading: [1] [2]

Plant Architecture and Its Evolutionary Implications

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[SOURCE]

I make it a point that during my field season I enjoy my breakfast out on the deck. It is situated about halfway up the canopy of the surrounding forest and offers a unique perspective that is hard to come by elsewhere. Instead of looking up at the trees, I am situated in a way that allows for a better understanding of the overall structure of the forest. Its this perspective that generates a lot of different questions about what it takes to survive in a forested ecosystem, especially as it relates to sessile organisms like plants.

Quite possibly my favorite plants to observe from the deck are the pagoda dogwoods (Cornus alternifolia). Hinted at by its common name, this wonderful small tree takes on a pagoda-like growth form with its stacked, horizontal branching pattern. It is unmistakable against the backdrop of other small trees and shrubs in the mid canopy. The fact that it, as well as many other plant species, can be readily recognized and identified on shape alone will not be lost on most plant enthusiasts.

The fact that diagrams like these exist in tree guides is proof of the utility of this concept.

Even without the proper vocabulary to describe their forms, anyone with a keen search image understands there is a gestalt to most species and that there is more to this than simply fodder for dichotomous keys. The overall form of plants has garnered attention from a variety of disciplines. Such investigations involve fields of study like theoretical and quantitative biology to engineering and biomechanics. It has even been used to understand how life may evolve on other planets. It is a fascinating field of investigation and one worth spending time in the literature. 

Some of the pioneering work on this subject started with two European botanists: Dr. Francis Hallé and Dr. Roelof Oldeman. Together they worked on conceptual models of tree architecture. Using a plethora of empirical studies on whether a tree branches or doesn't, where branches occurs, how shoots extend, how branches differentiate, and whether reproductive structures are terminal or lateral, they were able to reduce the total number of tree forms down to 23 basic architectural models (pictured above). Each model describes the overall pattern with which plants grow, branch, and produce reproductive structures. At the core of these models is the concept of reiteration or the repitition of form in repeatable sub-units. The models themselves were given neutral names that reflect the botanists that provided the groundwork necessary to understand them.  

Despite the fact that these models are based on investigations of tropical tree species, they are largely applicable to all plant types whether they are woody or herbaceous and whether they occur in the temperate zone or the tropics. The models themselves do not represent precise categories but rather points on a spectrum of architectural possibilities. Some plants may be intermediate between two forms or share features of more than one model. It should also be noted that most trees conform to a specific model for only a limited time period during their early years of development. Random or stochastic events throughout a trees life greatly influence its overall structure as it continues to grow. The authors are careful to point out that a trees crown is the result of all the deterministic, opportunistic, and chance events in its lifetime.  

Despite these exceptions, the adherence of most plants to these 23 basic models is quite astounding. Although many of the 23 models are only found in the tropics (likely an artifact of the higher number of species in the tropics than in the temperate zones), they provide accurate reference points for further study. For instance, the restriction of some growth forms to the tropics raises intriguing questions. What is it about tropical habitats that restricts models such as Nozeran's (represented by chocolate - Theobroma cacao) and Aubréville's (represented by the sea almond - Terminalia catappa) to these tropical environments? It likely has to do with the way in which lateral buds develop. In these models, buds develop without a dormancy stage, a characteristic that is not possible in the seasonal climates of the temperate zones. 

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Reiteration is an important process in plant architectural development in which plants repeat their basic model. This is especially important in repairing damage. [SOURCE]

Another interesting finding borne from these models is that there doesn't seem to be strong correlations between architecture and phylogeny. Although species within a specific genus often share similar architecture, there are plenty of exceptions. What's more, the same form can occur in unrelated species. For instance, Aubréville's model occurs in at least 19 different families. Similarly, the family Icacinaceae, which contains somewhere between 300 and 400 species, exhibits at least 7 of the different models. Alternatively, some families are architecturally quite simple. For instance the gymnosperms are considered architecturally poor, exhibiting only 4 of the different models. Even large families of flowering plants can be architecturally simplistic. Take the Fabaceae, which is largely comprised of plants exhibiting Troll's model. 

So, at this point the question of what is governing these models becomes apparent. If most plants can be reduced to these growth forms at some point in their life then there must be some aspect of the physical world that has shaped their evolution through time. Additionally, how does plant architecture at the physical level scale up to the level of a forest? Questions such as this are fundamental to our understanding of not only plants as organisms, but the role they play in shaping the world around us. 

Although many scientists have attempted to tackle these sorts of questions, I want to highlight the work of one individual in particular - Dr. Karl Niklas. His work utilizes mathematics to explain plant growth and form in relation to four basic physical constraints:

1) Plants have to capture sunlight and avoid shading their own leaves.

2) Plants have to support themselves structurally.

3) Plants have to conduct water to their various tissues.

4) Plants must be able to reproduce effectively.

Using these basic constraints, Dr. Niklas built a mathematical simulation of plant evolution. His model starts out as a "universe" containing billions of possible plant architectures. The model then assesses each of these forms on how well they are able to grow, survive, and reproduce through time. The model is then allowed to change environmental conditions to assess how these various forms perform and how they evolve. 

An example of Niklas' model showing how simple branching pattern (bottom) can evolve over time into more complex, yet familiar, forms (top).

The most remarkable part of this model is that it inevitably produces all sorts of familiar plant forms, such as those we see in lycophytes, ferns, as well as many of the tree architectural models mentioned above. What's more, later iterations of the model do an amazingly accurate job at predicting forest structure dynamics such as self-thinning, mortality, and realistic size/frequency distributions of various species. 

It would appear that the rules governing what we know as a plant are to some degree universal. Because constraints such as light capture and the passive movement of water are firmly grounded in the laws of physics, it makes sense that the successful plant architectures we know and love today (as well as those present through the long history of plant evolution on this planet) are in large part a result of these physical constraints. It also begs the question of what photosynthetic life would look like on other planets. It is likely that if life arose and made its living in a similar way, familiar "plant" architecture could very well exist on other planets.

Listen to my interview with Dr. Karl Niklas here.

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3] [4] [5]