Are Crickets Dispersing Seeds of Parasitic Plants?

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Parasitic plants lead unique lifestyles. Many have foregone photosynthesis entirely by living off fungi or their photosynthetic neighbors. Indeed, there are many anatomical and physiological adaptations that are associated with making a living parasitically. Whether they are full parasites or only partial, one thing that many parasitic plants have in common are tiny, dust-like seeds. Their reduced size and thin seed coats are generally associated with wind dispersal, however, there are always exceptions to the rule. Recent evidence has demonstrated that a handful of parasitic plants have evolved in response to a unique seed dispersal agent - camel crickets.

A research team based out of Japan recently published a paper describing a rather intriguing seed dispersal situation involving three species of parasitic plants (Yoania amagiensis - Orchidaceae, Monotropastrum humile - Ericaceae, and Phacellanthus tubiflorus - Orobanchaceae). These are all small, achlorophyllous herbs that either parasitize trees directly through their roots or they parasitize the mycorrhizal fungi associated with said trees. What's more, each of these species are largely inhabitants of the dense, shaded understory of rich forests.

These sorts of habitats don't lend well to wind dispersal. The closed forest canopy and dense understory really limits wind flow. It would appear that these three plant species have found away around this issue. Each of these plants invest in surprisingly fleshy fruits for their parasitic lifestyle. Also, their seeds aren't as dust-like as many of their relatives. They are actually very fleshy. This is odd considering the thin margins many parasitic plants live on. Any sort of investment in costly tissues must have considerable benefits for the plants if they are to successfully get their genes into the next generation.

Fleshy fruits like this are usually associated with a form of animal dispersal called endozoochory. Anyone that has ever found seed-laden bird poop understands how this process works. Still, simply getting an animal to eat your seeds isn't necessarily enough for successful dispersal. Seeds must survive their trip through the gut and come out the other end relatively in tact for the process to work. That is where a bit of close observation came into play.

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After hours of observation, the team found that the usual frugivorous suspects such as birds and small mammals showed little to no interest in the fruits of these parasites. Beetles were observed munching on the fruits a bit but the real attention was given by a group of stumpy-looking nocturnal insects collectively referred to as camel crickets. Again, eating the fruits is but one step in the process of successful seed dispersal. The real question was whether or not the seeds of these parasites survived their time inside either of these insect groups. To answer this question, the team employed feeding trials.

They compared seed viability by offering up fruits to beetles and crickets both in the field and back in the lab. Whereas both groups of insects readily consumed the fruits and seeds, only the crickets appeared to offer the greatest chances of a seed surviving the process. Beetles never pooped out viable seeds. The strong mandibles of the beetles fatally damaged the seeds. This was not the case for the camel crickets. Instead, these nocturnal insects frequently pooped out tens to hundreds of healthy, viable seeds. Considering the distances the crickets can travel as well as their propensity for enjoying similar habitats as the plants, this stacks up to potentially be a beneficial interaction. 

The authors are sure to note that these results do not suggest that camel crickets are the sole seed dispersal agents for these plants. Still, the fact that they are effective at moving large amounts of seeds is tantalizing to say the least. Taken together with other evidence such as the fact that the fruits of these plants often give off a fermented odor, which is known to attract camel crickets, the fleshy nature of their fruits and seeds, and the fact that these plants present ripe seed capsules at or near the soil surface suggests that crickets (and potentially other insects) may very well be important factors in the reproductive ecology of these plants.

Coupled with previous evidence of cricket seed dispersal, it would appear that this sort of relationship between plants and crickets is more widespread than we ever imagined. It is interesting to note that relatives of both the plants in this study and the camel crickets occur in both temperate and tropical habitats around the globe. We very well could be overlooking a considerable component of seed dispersal ecology via crickets. Certainly more work is needed.

Photo Credits: [1]

Further Reading: [1] [2]

A Common Plant With An Odd Pollination Mechanism

Photo by Kerry Woods licensed under CC BY-NC-ND 2.0

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

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

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

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

Photo by Matthew Beziat licensed under CC BY-NC 2.0

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

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

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

Photo Credit: [1] [2]

Further Reading: [1] [2]

Arctic Foxes: The Unintentional Gardeners

Predators are an integral component of any healthy ecosystem. Their influence can even be felt at the botanical level via what are called top-down controls. Either through direct predation or through altering their behavior, predators influence the herbivores in any system, which usually results in healthier plant communities. This method is rather indirect but new evidence shows that in the Arctic tundra, a top predator is having quite a direct influence on plant communities.

What's not to love about Arctic foxes? All anthropomorphic views aside, Arctic foxes are important predators in this ecosystem. Although the food web complexity on the tundra is largely driven by limits to plant productivity, a paper published in 2016 shows that these little canids can have profound effects on vegetation. This doesn't have to do with predation directly but rather their reproductive behavior. 

Arctic foxes live, give birth, and raise their young in underground dens. Without these subterranean homes, the foxes would be much more vulnerable to other predators as well as the harsh Arctic climate. Dens don't happen overnight either. Suitable sites are tended for generations and some dens may well be more than a century old. All this equates to a lot of activity in and around a good den site. 

With an average litter size of 8 - 10 pups per female, one can imagine the food and waste buildup must be considerable. Like all predators, Arctic fox food and waste are rich in nitrogen and phosphorus compounds, the necessary building blocks of life. Many an onlooker has noticed that, unsurprisingly, plant growth around Arctic fox dens is much more lush than on the surrounding landscape. Until recently though, such differences have hardly been quantified.

Arctic Fox (Vulpes lagopus) photo by Allan Hopkins licensed under CC BY-NC-ND 2.0

By examining the soil and plant characteristics around Artic fox dens in Canada and comparing these data to surrounding sites without Arctic fox dens, a team of researchers put the first comprehensive numbers to the effects of Arctic foxes on tundra plant communities. They found that soils from in and around Arctic fox dens contained significantly higher levels of nitrogen and phosphorus than did the surrounding control plots. What's more, these levels varied throughout the year. In June, for instance, soil nitrogen and phosphorus levels were 71% and 1195% higher than non-den soils. These levels seemed to switch later in the summer. In August, soil nitrogen from fox dens were 242% higher and soil phosphorus levels were 191% higher.

As you can probably imagine, all of these extra nutrients caused a change in vegetation around the dens. Den sites were far more productive in terms of vegetation. The team found that, on average, Arctic fox dens supported 2.8 times more plant biomass than did the surrounding area. The authors note that these were conservative estimates and that the true values are much higher. Taken together, these results demonstrate that far from simply being top predators, Arctic foxes are true ecosystem engineers, at least on local scales. This is especially important in such a demanding ecosystem as the Arctic tundra.

Photo Credits: [1] [2]

Further Reading: [1]

Meet the Sweetfern

Photo by Sten Porse licensed under CC BY-SA 3.0

I remember the first time I laid my eyes on Comptonia peregrina. I was new to botany at that point in my life so I didn't have a well developed search image for these sorts of things. I was scrambling down a dry ridge with a scattered overstory of gnarly looking chestnut oaks when I saw a streak of green just below me on a sandy outcropping. They were odd looking plants, the likes of which I had never seen before.

I took out my binoculars to get a better look. What were these strange organisms? Were they ferns? No, they seemed to have woody stems. Were they gymnosperms? No, I could make out what appeared to be male catkins. Luckily I never leave home without a field guide or two. Using what little terminology I knew, I was able to narrow my focus to a plant commonly called a "sweetfern."

Photo by Megan Hansen licensed under CC BY-SA 2.0

This was one of the first instances in which I grasped just how troublesome common names can be. C. peregrina is mostly definitely not a fern. It is actually an angiosperm that hails from the bay family (Myricaceae). Comptonia is a monotypic genus, with C. peregrina being the only species. It is a denizen of dry, nutrient poor habitats. As such, it has some wonderful adaptations to deal with these conditions.

To start with, its a nitrogen fixer. Similar to legumes, it forms nodules on its roots that house specialized nitrogen-fixing bacteria called rhizobia. This partnership takes care of its nitrogen needs, but what about others? One study found that not only do the roots form nodules, they also form dense cluster roots. Oddly, closer observation found that these clusters were not associated with mycorrhizal fungi. What's more, they also found that these structures were most prevalent in highly disturbed soils. It is thought that this is one way that the plant can maximize its uptake of phosphorus under the harshest growing conditions. 

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Photo by Jomegat licensed under CC BY-SA 3.0

Flowering in this species is not a showy event. C. peregrina can be monoecious or dioecious, producing male and female catkins towards the ends of its shoots. After fertilization, seeds develop inside bristly fruits. Seed banking appears to be an important reproductive strategy for this species. One study found that germinated seeds had lain dormant in the soil for over 70 years until disturbance opened up the canopy above. It is expected that seeds of this species could exhibit dormancy periods of a century or more. 

In total, this is one spectacular species. Not only does it have a unique appearance, it is also extremely hardy and an excellent species to plant in drought-prone soils wherever it is native. I do see it in landscaping from time to time. If you encounter this species in the wild, take the time to observe it in detail. You will be happy you did!

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

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

More to Tall Boneset Than Meets the Eye

For most of the growing season, tall 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 gene’s 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 made up entirely of females. In fact, only populations found in the Ozark Mountains were found to produce sexually viable flowers with male and female organs. This is 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. 

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 very 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

Photo by Dinesh Valke from Thane, India licensed under CC BY-SA 2.0

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 a cousin of the amaranths. You can imagine my surprise then when I recently learned that this hardy species is actually a member of the sunflower 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. 

Photo by Dinesh Valke from Thane, India licensed under CC BY-SA 2.0

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 hardy but in reality, they are often a bit picky about when and where they will grow. For that reason, seed banking is super important. Not every year will produce favorable growing 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

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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]

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]

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]

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]

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]

Eastern North America's Temperate Rainforest

I have often remarked that working in the southern Appalachian Mountains during the summer feels more like working in a rainforest than it does an eastern deciduous forest. Lots of rain, high humidity, and a bewildering array of flora and fauna conjure up images of some far away jungle. Only winter can snap this view out of ones head. I recently learned, however, that these feelings are not misplaced. Indeed, this region of southern Appalachia is considered a temperate rainforest. 

These mountains are old. They arose some 480 million years ago and have been shaping life in this region of North America ever since. Another thing these mountains are quite good at is creating their own weather systems. Here in southern Appalachia, warm, wet air from the Gulf of Mexico and western Atlantic blows northward until it hits the Appalachian Mountains. The mountainous terrain comprising parts of Pisgah, Nantahala, and Chattahoochee National Forests has been referred to as "the Blue Wall" and is responsible for the unique conditions that created this temperate rainforest.

As this air rises over their peaks, it begins to cool. As it does, water in the air condenses. This results in torrents of rain. On average, this area receives anywhere from 60 to 100+ inches of rain every year. The Appalachian temperate rainforest is second only to the Pacific Northwest in terms of rainfall in North America. All of this water and heat coupled with the age and relative stability of this ecosystem over time has led to the explosion of biodiversity we know and love today. 

Life abounds in the southern Apps. The plant diversity can be rather intimidating as species from the north mix with those coming up from the south. For instance, there are more tree species in these mountains than in all of Europe.  Rates of endemism in these mountains, both in terms of flora and fauna, are remarkable. There are relics of bygone eras that never expanded their range following repeated glaciations. What's more, a multitude of species combinations can be found as you go from low to high elevations. 

At lower elevation, forests are dominated by American beech (Fagus grandifolia), yellow birch (Betula alleghaniensis), maple (Acer spp.), birch (Betula spp.), and oak (Quercus spp.). Magnolias cover the humid coves. Mid elevations boast birches, mountain ash (Sorbus americana), and mountain maple (Acer spicatum). High elevations contain fraser fir (Abies fraseri) and redspruce (Picea rubens). Both the understory and the the mountain balds are home to a staggering array of different Heaths (Ericaceae). From Rhododendrons to azaleas and mountain laurels, the colors are like those lifted from an abstract painting. The forest floor is where I focus most of my energy. It is hard to capture the diversity of this habitat in only a few paragraphs. What I can say is that I haven't even scratched the surface. It seems like there is something new to see around every corner. 

The point I am trying to make is that this region is quite special. It is something worth protecting. From development to mining and changes in temperature and precipitation, human activities are exacting quite a toll on the Appalachian Mountains. The system is changing and there is no telling what the future is going to look like. Conserving wild places is a must. There is no way around it. Luckily there is a reason people love this place so very much. There are a lot of dedicated folks out there working to protect and conserve everything that makes southern Appalachia what it is. Get out there, enjoy, and support your local land trust!

Further Reading:  [1] 

Pitcher's Thistle and the Dunes It Calls Home

Sand dunes are harsh habitats for any organism to make a living. They are hot, they are low in nutrients, water doesn't stick around for very long, and they can be incredibly unstable. Despite these obstacles, dunes around the world host rather unique floras comprised of plants well suited to these conditions. Sadly, we humans have been pretty good at destroying many of these dune habitats. This is especially true along the shores of the Great Lakes. To put this in perspective, I would like us to take a closer look at a special Great Lakes dune denizen. 

Meet Pitcher's thistle (Cirsium pitcheri). It is a true dune plant and is endemic to the shores of the upper Great Lakes. Its a rather lanky plant, often looking as if it is having a hard time supporting its own weight. Despite its unkempt look, adult plants can reach heights of 3 feet, which is quite impressive given where it lives. It is covered in silvery hairs, giving the plant a shiny appearance. These hairs likely protect the plant from the onslaught of sun, abrasive wind-blown sand, and desiccation. One of the benefits of growing in such inhospitable places is that historically speaking, Pitcher's thistle could grow with little competition. Individual plants grow for roughly 5 to 8 years before flowering. After seeds are produced, the plant dies. The seedlings are then free to develop without being shaded out. 

The last century or so have not been good to Pitcher's thistle. Shoreline development, altered disturbance regimes, and isolation of various populations have fragmented its range and reduced its genetic diversity. To make matters worse, its remaining habitat is still shrinking. Shoreline development has altered wave action that is vital to these dune habitats. Waves that once brought in new sediments and built dunes are largely carving away what's left. They are eroding at an alarming rate that even dune-adapted plants like Pitcher's thistle can't keep up with. Recreational use of these habitats adds another layer as heavy foot traffic carves deep scars into these dunes, furthering their demise. 

One silver lining in all of this is that dedicated researchers are paying close attention to the natural history of this species. They have discovered some fascinating things that will help in the recovery of this special plant. For instance, it has been observed that although trampling doesn't necessarily kill Pitcher's thistle, it does damage sensitive buds. This often results in plants developing multiple flower heads. Although this sounds like a benefit, researchers discovered that these damaged plants actually produce fewer viable seeds despite producing more flowers. 

Gary B. Walton / USFWS Public Domain

Also, they have found that American goldfinches are playing a considerable role in its reproductive success. Despite the tightly clasping, spiny bracts that protect the seeds, goldfinches have been found to reduce seed production by 90% as they forage for food and the fluffy seed hairs for nest building. Evidence suggests that goldfinches are more likely to target small, isolated populations of Pitcher's thistle rather than large, contiguous patches. The reason for this is anyone's guess but it does suggest that they way around this issue is to supplement dwindling populations with new plants grown from seed. 

Without intervention, it is very likely that Pitcher's thistle would go extinct in the near future. Luckily, researchers and federal officials are teaming up to make sure that doesn't happen. Long term population monitoring is in place throughout its range and a sandbox technique has been developed for germinating and growing up new individuals to supplement wild populations. Through habitat restoration efforts, supplementing of existing and the creation of new populations, the future of this charismatic dune thistle has gotten a little bit brighter. It isn't out of the metaphorical woods but there is reason for hope. 

Photo Credit: [1] 

Further Reading: [1]

Who Pollinates the Flame Azalea?

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

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

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

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

Photo by Jay Williams licensed under CC BY-NC 2.0

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

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

Photo Credit: [1]

Further Reading: [1]

The Grasstree of Southwestern Australia

Taken by John O'Neill licensed under CC BY-SA 3.0

Southwestern Australia is home to a wonderful and unique flora. A combination of highly diverse, nutrient-poor soil types, bush fires, and lots of time have led to amazing adaptive radiations, the result of which are myriad plant species found nowhere else in the world. One of the most incredible members of southwestern Australia's flora is the grassplant (Kingia australis). Like all plants of this region, it is one hardy species.

The taxonomic history of the grassplant has been a bit muddled. As its common name suggests, it was once thought to be a type of grasstree (genus Xanthorrhoea), however, its resemblance to this group is entirely superficial. It has since been placed in the family Dasypogonaceae. Along with three other genera, this entire family is endemic to Australia. Growing in southwestern Australia presents lots of challenges such as obtaining enough water and nutrients to survive and for the grassplant, these have been overcome in some fascinating ways.

The way in which the grassplant manages this is incredible. Its trunk is not really a true trunk but rather a dense cluster of old leaf bases. Within this pseudotrunk, the grassplant grows a series of fine roots. Research has shown this to be an adaptation to life in a harsh climate. Because water can be scarce and nutrients are in short supply, the grassplant doesn't take any chances. Water hitting the trunk is rapidly absorbed by these roots as are any nutrients that come in the form of things like bird droppings.

Photo by Casliber licensed under CC BY-SA 3.0

Coupled with its underground roots, the grassplant is able to eek out a living in this dry and impoverished landscape. That being said, its life is spent in the slow lane. Plants are very slow growing and estimates place some of the larger individuals at over 600 years in age. Its amazing how some of the harshest environments can produce some of the longest lived organisms.

As you can probably imagine, reproduction in this species can also be a bit of a challenge. Every so often, flower clusters are produced atop long, curved stems. Their production is stimulated by fire but even then, with nutrients in poor supply, it is not a frequent event. Some plants have been growing for over 200 years without ever producing flowers. This lifestyle makes the grassplant sensitive to disturbance. Recruitment is limited, even in good flowering years and plants take a long time to mature. That is why conservation of their habitat is of utmost importance.

Photo Credits: [1] [2]

Further Reading: [1] [2]

The Mighty 'Ama'u

Photo by Forest Starr and Kim Starr licensed under CC BY 2.0

We tend to think of ferns as fragile plants, existing in the shaded, humid understories of forests. This could not be farther from the truth. Their lineage arose on this planet some 360 million years ago and has survived countless extinctions. In truth, they exhibit a staggering array of lifestyles, each with its own degree of adaptability. Take the Hawaiian tree fern, Sadleria cyatheoides for example.

Known in Hawai'i as the 'Ama'u, this tree fern is one of the first species to colonize the barren lava flows that make the Big Island so famous. This is an incredibly harsh landscape and many challenges must be overcome in order to persist. This does not seem to be an issue for the 'Ama'u. It is just as much at home in these water-starved habitats as it is in wetter forests. It is easily the most successful species in this genus, having colonized every island in the archipelago.

Photo by John Game licensed under CC BY 2.0

Much of its success has to due with a part of its life cycle that is much less obvious to us - the gametophyte stage. The tree fern we see is only half of the story. It is the spore-producing phase conveniently referred to as the sporophyte. When a spore finds a suitable site for germination, it grows into the other half of the life cycle, the gametophyte. This minute structure looks like a tiny green heart and it houses the reproductive organs of the plant. When water is present, male gametophytes release their flagellated sperm, which swim around until they find a female gametophyte to fertilize. Once fertilized, the resulting embryos will then grow into a new tree fern and start the cycle anew.

What sets the 'Ama'u apart from its rarer cousins is the fact that its gametophyte appears to be quite capable of both outcrossing and self-fertilization. Outcrossing, of course, promotes genetic diversity, however, the ability to self-fertilize means that a new plant can grow from only a single spore. This is super advantageous when it comes to colonizing new habitats. Its cousins seem to lack this ability to self-fertilize successfully, restricting them to more localized areas. Taken together, I think it's safe to say that the 'Ama'u is one tough cookie. 

Photo Credits: [1] [2]

Further Reading: [1] [2]