Giant Ferns

Although the days of forests full of towering pteridophytes has long since vanished, a few giants still remain. Some of the largest ferns alive today hail from the genus Angiopteris and they are truly massive. To stand beneath their fronds is to be transported back hundreds of millions of years.

The mule's foot ferns (as they are commonly referred to) belong to an ancient lineage. The family, Marattiaceae, is thought to have diverged from the more familiar fern lineages very early on in their evolutionary history. As such, they have more in common with the grapeferns (Ophioglossales), whisk ferns (Psilotales), and horsetails (Equisetales) than they do more familiar extant ferns. One of the more bizarre qualities of this genus is the way in which they disperse their spores. A pressure differential is created inside the sporangium that eventually leads to cavitation. As the air space within implodes, the spores are launched outwards from the fronds at high speeds.

The most obvious feature, however, is their size. Angiopteris are some of the largest ferns on our planet. Arising from an odd looking globular mass are massive fiddle heads. These gradually unfurl into fronds of epic proportions. The record for frond size goes to Angiopteris evecta. An individual growing in Java produced fronds that were 29 feet 6 inches (9 meters) long! Amazingly enough, these fronds are capable of moving up or down depending on the weather.

Such movements are no small feat for a frond of that size. It is all thanks to an area of the petiole known as the pulvinus. The pulvini are swollen regions at the base of the petiole that expand or contract based on water pressure within. Angiopteris evecta produces the largest pulvini of any plant in the world.

Angiopteris can be found growing native from Madagascar and throughout vairous islands of the South Pacific. It is hard to get an accurate species count as the taxonomic status of many "species" are still up for debate. Although something like 200 species have been described, only a small handful of these are recognized in most modern floras. Sadly, many of these are threatened by habitat loss in their home range. The same can't be said elsewhere. Some Angiopteris have become quite invasive in places like Hawai'i and Jamaica. Because of their unique evolutionary history, their bizarre appearance, and their massive size, they been planted far outside of their native range. Research has shown that many of these ferns are much more tolerant of varying environmental conditions than that of their native forests, making any new introductions quite risky.

Photo Credits: [1] [2]

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

Captive Pollinators

In order to ensure pollination, leafflower trees in the genus Glochidion have entered into an intimate relationship with a small family of moths. Their flowers have become so specialized that no other insect is capable of pollinating them. In return, female moths are provided with an edible place to lay their eggs - the fruit of the tree. One species of leafflower has taken this relationship to the extreme. It holds its pollinators captive. In order to understand this bizarre relationship, we must first take a closer look at this interesting pollination syndrome.

Ecologists refer to this type of pollination syndrome as "brood pollination." In the case of the leafflower trees, pollination is achieved thanks to female moths known commonly as leafflower moths. Gravid female leafflower moths locate the blooms thanks to a special perfume tailored specifically for each species. The females first visit the male flowers where they pick up some pollen. Next they visit the female flowers where they will then deposit the pollen into a special chamber that can only be accessed by the female moths' proboscis.

After pollination, the female leafflower moth will then locate the ovaries of the flower and using a needle-like ovipositor, will deposit eggs within the undeveloped fruits. The larvae within eventually hatch right next to their food source - leafflower seeds. The larvae aren't gluttons. They will only eat one or two of the dozens of seeds developing within the fruit. Although this may seem wasteful on the part of the plant, it makes a lot of sense from an evolutionary perspective. Essentially it reduces the likelihood that the moths will try to cheat the system. Glutenous larvae that eat more than one or two seeds will be penalized in the long run because fewer host plants will be available. By tying the reproductive abilities of the moth to the production of fruit, the tree ensures regular pollination.

For most of the leafflower/moth pairs, once the seed meal is over, the larvae chew out of the fruit and fall to the ground to pupate. However, this is not the case for a leafflower known scientifically as Glochidion lanceolarium. It takes this relationship a step further by holding the larvae captive for nearly a year.

Cut open an fruit of this leafflower and there is a chance you might find a fully formed moth waiting patiently inside one of the swollen chambers. Instead of chewing out before it pupates, the moth is held captive within. Only when the fruits mature and split open will the moths be released. This happens just as the new crop of flowers is opening. The tree is literally controlling when its obligate pollinator is available to do its reproductive bidding.

The uniquely intimate nature of this relationship goes beyond simply being interesting. By studying how these two partners interact in relation to the other leafflower/moth partners around the Old World tropics researchers are gaining a better understanding of how such mutualisms evolve.

Photo Credits: [1] [2]

Further Reading: [1]

On Fungi and Forest Diversity

One simply can't talk about plants without eventually talking about fungi. The fact of the matter is the vast majority of plant species rely on fungal interactions for survival. This mutualistic relationship is referred to as mycorrhizal. Fungi in the soil colonize the root system of plants and assist in the acquisition of nutrients such as nitrogen and phosphorus. In return, most photosynthetic plants pay their mycorrhizal symbionts with carbohydrates. 

There are two major categories of mycorrhizal fungi - ectomycorrhizae (EMF) and arbuscular mycorrhizae (AMF). Though there are a variety of different species of fungi that fall into either of these groups, their strategies are pretty much the same. EMF make up roughly 10% of all the known mycorrhizal symbionts. The prefix "ecto" hints at the fact that these fungi form on the outside of root cells. They form a sort of sheath that encases the outside of the root as well as a "hartig net" around the outside of individual cells within the root cortex. AMF, on the other hand, literally penetrate the root cells and form two different kinds of structures once inside. One of these structures looks like the crown of a tree, hence the term "arbuscular." What's more, they are considered the oldest mycorrhizal group to have evolved. 

The type of mycorrhizal fungi a plant partners with has greater implications that simple nutrient uptake. Evidence is now showing that the dominant fungi of a region can actually influence the overall health and diversity forest ecosystems. The mechanism behind this has a lot to do with the two different categories discussed above. 

Researchers have discovered that trees partnering with AMF experience negative feedbacks in biomass whereas those that partner with EMF experience positive feedbacks in biomass. When grown in soils that previously harbored similar tree species, trees that partnered with AMF grew poorly whereas trees that partnered with EMF grew much better. Additionally, by repeating the experiments with seedlings, researchers found that seedling survival was reduced for AMF trees whereas seedling survival increased in EMF trees. 

What is going on here? If mycorrhizae are symbionts, why would there be any detrimental effects? The answer to this may have something to do with soil pathogens. Thinking back to the major differences between EMF and AMF, you will remember that it comes down to the way in which they form their root associations. EMF form a protective sheath around the roots whereas AMF penetrate the cells.  As it turns out, this has major implications for pathogen resistance. Because they form a sheath around the entire root, EMF perform much better at keeping pathogens away from sensitive root tissues. The same can't be said for AMF. Researchers found that AMF trees experienced significantly more root damage when grown in soils that previously contained AMF trees. 

The differences in the type of feedback experienced by EMF and AMF trees can have serious consequences for tree diversity. Because EMF trees are healthier and experience increased seedling establishment in soils containing other EMF species, it stands to reason that this would lead to a dominance of EMF species, thus reducing the variety of species capable of establishing in that area. Conversely, areas dominated by AMF trees may actually be more diverse due to the reduction in fitness that would arise if AMF trees started to dominate. Though they are detrimental, the negative feedbacks experienced by AMF trees may lead to healthier and more diverse forests in the grand scheme of things. 

Infographic by [1]

Further Reading: [1]

 

 

Semi-Aquatic Orchids

By Jim Fowler. Copyright © 2017

By Jim Fowler. Copyright © 2017

Orchids have conquered nearly every continent on this planet except for Antarctica. In fact, there seems to be no end to the diversity in color, form, and habit of the world's largest family of flowering plants. Still, it might surprise many to learn that some orchids have even taken to water. Indeed, at least three species of orchid native to Latin and North America as well as a handful of islands have taken up a semi-aquatic lifestyle.

Most commonly encountered here in North America is the water spider orchid (Habenaria repens). It is a relatively robust species, however, considering that even its flowers are green, it is often hard to spot. Though it will root itself in saturated soils along the shore, it regularly occurs in standing water throughout the southeast. Often times, it can be found growing amidst other aquatic plants like pickerel weed (Pontederia cordata) and duck potato (Sagittaria latifolia). Because it can reproduce vegetatively, it isn't uncommon to find floating mats of comprised entirely of this orchid.  

By Jim Fowler. Copyright © 2017

By Jim Fowler. Copyright © 2017

Living in aquatic habitats comes with a whole new set of challenges. One of these is exposure to a new set of herbivores. Crayfish are particularly keen on nibbling plant material. In response to this, the water spider orchid has evolved a unique chemical defense. Coined "habenariol," this ester has shown to deter freshwater crayfish from munching on its leaves and roots. Another challenge is partnering with the right fungi. Little work has been done to investigate what kinds of fungi these aquatic orchids rely on for germination and survival. At least one experiment was able to demonstrate that the water spider orchid is able to partner with fungi isolated from terrestrial orchids, which might suggest that as far as symbionts are concerned, this orchid is a generalist.

The flowers of the water spider orchid are relatively small and green. What they lack in flashiness they make up for in structure and scent. The flowers are quite beautiful up close. The slender petals and long nectar spur give them a spider-like appearance. At night, they emit a vanilla-like scent that attracts their moth pollinators. 

Photo Credits: Jim Fowler. Copyright © 2017 www.jfowlerphotography.com

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

Orchid Dormancy Mediated by Fungi

North America's terrestrial orchids seem to have mastered the disappearing act. When stressed, these plants can enter into a vegetative dormancy, existing entirely underground for years until the right conditions return for them to grow and bloom. Cryptic dormancy periods like this can make assessing populations quite difficult. Orchids that were happy and flowering one year can be gone the next... and the next... and the next...

How and why this dormancy is triggered has confused ecologists and botanists alike. Certainly stress is a factor but what else triggers the plant into going dormant? According to a recent paper published in the American Journal of Botany, the answer is fungal.

Orchids are the poster children for mycorrhizal symbioses. Every aspect of an orchid's life is dependent on these fungal interactions. Despite our knowledge of the importance of mycorrhizal presence in orchid biology, no one had looked at how the abundance of mycorrhizal fungi influenced the life history of these charismatic plants until now.

By observing the presence and abundance of a family of orchid associated fungi known as Russulaceae, researchers found that the abundance of mycorrhizal fungi in the environment is directly related to whether or not an orchid will emerge. The team focused on a species of orchid known commonly as the small whorled pogonia (Isotria medeoloides). Populations of this federally threatened orchid are quite variable and assessing their numbers is difficult.

The team found that the abundance of mycorrhizal fungi is not only related to prior emergence of these plants but could also be used as a predictor of future emergence. This has major implications for orchid conservation overall. It's not enough to simply protect orchids, we must also protect the fungal communities they associate with.

Research like this highlights the need for a holistic habitat approach to conservation issues. So many species are partners in symbiotic relationships and we simply can't value one partner over the other. If conditions change to the point that they no longer favor the mycorrhizal partner, it stands to reason that it would only be a matter of years before the orchids disappeared for good.

Photo Credit: NC Orchid

Further Reading: [1]

A Unique Passionflower Endemic to Costa Rica

I love small flowers, especially if they pack in a lot of detail. That's is why this passion flower caught my eye. Meet Passiflora boenderi, a charismatic vine endemic to a small region of Costa Rica. Apparently this species had been sitting around in herbaria for years under a different name. It wasn't until living specimens were observed that botanists realized it is a distinct species.

There is a lot to look at on this species. The flowers themselves are some of the smallest in the genus. They pack in all of the detail of a larger passion flower, just in miniature. The leaves are quite stunning as well. They're bilobed with a tinge of purple and covered in bright, orange-yellow spots. The spots themselves serve an important role in protecting this plant from herbivores.

The genus Passiflora is part of an intense evolutionary arms race with a genus of butterfly known as Heliconius. Their caterpillars feed on the foliage of passion flowers. As such, Passiflora have evolved a variety of means that help them to avoid the attention of gravid female butterflies. The orange spots on the leaves of P. boenderi are one such adaptation and they serve a dual function.

The first is a visual deterrent. Female Heliconius prefer to lay their eggs on caterpillar-free leaves. This makes sense. Why bother laying eggs where there will be ample competition for food. The spots mimic, both in size and shape, the appearance of Heliconius eggs. A female looking for a spot to lay will see these spots and move on to another plant. In addition to the visual mimicry, these spots also secrete nectar. The energy-rich nectar inevitably attracts ants, which viciously defend them as a food source. If a caterpillar (or any other herbivore fore that matter) were to start munching on the leaves, the ants quickly drive them off.

Because of its limited range, P. boebderi is under threat of extinction. Habitat destruction of its lowland habitat for palm oil, pineapples, and vacation resorts is an ongoing threat to the long term survival of this species and many others. I was fortunate enough to have encountered this plant growing in the Cliamtron at the Missouri Botanical Garden but I fear that if we keep on doing what we humans are so good at, botanical gardens may be the only place this species will be found growing in the not too distant future.

Further Reading: [1] [2]

The Longleaf Pine: A Champion of the Coastal Plain

As far as habitat types are concerned, the longleaf pine savannas of southeastern North America are some of the most stunning. What's more, they are also a major part of one of the world's great biodiversity hotspots. Sadly, they are disappearing fast. Agriculture and other forms of development are gobbling up the southeast coastal plain at a bewildering rate. For far too long we have ignored, or at the very least, misunderstood these habitats. Today I would like to give a brief introduction to the longleaf pine and the habitat it creates.

The longleaf pine (Pinus palustris) is an impressive species. Capable of reaching heights of 100 feet or more, it towers over a landscape that boggles the mind. It is a landscape born of fire, of which the long leaf pine is supremely adapted to dealing with. These pines start out life quite differently than other pines. Seedlings do not immediately reach for the canopy. Instead, young long leaf pines spend their first few years looking more like a grass than a tree. Lasting anywhere between 5 to 12 years, the grass stage of development gives the young tree a chance to save up energy before it makes any attempt at vertical growth. 

The reason for this is fire. If young long leaf pines were to start their canopy race immediately, they would very likely be burned to death before they grew big enough to escape the harmful effects of fire. Instead, the sensitive growing tip is safely tucked away in the dense needle clusters. If a fire burns through the area only the tips of the needles will be scorched, leaving the rest of the tree safe and sound. During this stage, the tree is busy putting down an impressive root system. The taproot alone can reach depths of 6 to 9 feet!

Once a hardy root system has been formed and enough energy has been acquired, young longleaf pines go through a serious growth spurt. Starting in later winter or early spring, the grass-like tuft will put up a white growth tip called a candle. This tip shoots upwards quite rapidly, growing a few feet in only a couple of months. This is sometimes referred to as the bottlebrush phase because no horizontal branches are formed during this time. The goal at this point is to get the sensitive growing tip as far away from the ground as possible so as to avoid damaging fires. It is fun to encounter long leaf pines at this stage because like any young adult, they look a bit awkward.

Photo Credit: Woodlot - Wikimedia Commons

Photo Credit: Woodlot - Wikimedia Commons

Once the tree reaches about 6 to 10 feet in height, it will finally begin to produce horizontal branches. This doesn't stop its canopy bid, however, as it still will put on upwards of 3 feet of vertical growth each year! Every year its bark grows thicker and thicker, thus each year it becomes more and more resistant to fire. Far from being a force to cope with, fire unwittingly gives longleaf pines a helping hand by clearing the habitat of potential competitors that are less adapted to dealing with burns. After about 30 years of growth, longleaf pines reach maturity and will start to produce fertile cones.

Before European settlement, longleaf pine savanna covered roughly 90,000,000 acres of southeastern North America. Clearing and development have reduced that to a mere 5% of its former glory. For far too long its coastal plain habitat was thought to be a flat, monotonous region created by early human burning in the last few thousand years. We now know how untrue those assumptions are. Sure, the region is flat but it is anything but monotonous. Additionally, the coastal plain is one of the most lightning prone regions in North America. Fires would have been a regular occurrence long before any humans ever got there. 

Red indicates forest loss between 2011 and 2014. http://glad.umd.edu/gladmaps

Evidence suggests that this coastal plain habitat has remained relatively stable for the last 62,000 years. As such, it is full of unique species. Surveys of the southeastern coastal plain have revealed multiple centers of plant endemism, rivaled in North America only by the southern Appalachian Mountains. In fact, taken together, the coastal plain forests are widely considered one of the world's biodiversity hotspots! Of the 62,000 vascular plants found in these forests, 1,816 species (29.3%) are endemic. Its not just plants either. Roughly 1,400 species of fish, amphibians, reptiles, birds, and mammals rely on the coast plain forests for survival.

Luckily, we are starting to wake up to the fact that we are losing one of the world's great biodiversity hotspots. Efforts are being put forth in order to conserve and restore at least some of what has been lost. Still, the forests of southeastern North America are disappearing at an alarming rate. Despite comprising only 2% of the world's forest cover, the southern forests are being harvested to supply 12% of the world's wood products. This is simply not sustainable. If nothing is done to slow this progress, the world stands to lose yet another biodiversity hotspot. 

If this sounds as bad to you as it does to me then you probably want to do something. Please check out what organizations such as The Longleaf Alliance, Partnership For Southern Forestland Conservation, The Nature Conservancy, and The National Wildlife Federation are doing to protect this amazing region. Simply click the name of the organization to find out more.

Further Reading: [1] [2] [3] [4] 

Giant Trees Discovered in Africa

As far as tall trees are concerned, Africa has long been excluded from the list... until now. During a recent botanical survey of Mt. Kilimanjaro, a research team located a stand of large trees tucked away in a remote valley. Some of these trees were giants.

Tall trees are the result of a perfect storm of evolutionary history and unique environmental conditions. From the redwoods of the Pacific Coast to the Eucalyptus of Tasmania, rich soils, low levels of disturbance, and competition for light have driven some species to grow to mind boggling proportions. It seems fitting then that Africa's tallest mountain was hiding its tallest trees all this time. 

The species in question is known scientifically as Entandrophragma excelsum and belongs to the mahogany family (Meliaceae). A total of 13 giant E. excelsum were found during this expedition. Heights ranged from a modest 53.7 meters (176 ft) to a staggering 81.5 meters (267) in height! Unlike other species in this "Tall Tree Club," E. excelsum produces wood of surprisingly low density. However, it is thought that this low density wood, which is much less costly to produce, allows the trees to grow quick enough to avoid being overrun by vines before it can make it to the canopy. Indeed, very few E. excelsum were found to have vines growing on them. 

Although these are nowhere near the tallest trees in the world, they nonetheless break the African tall tree record, which was previously held by a non native Eucalyptus that died in 2006. The reason these African giants were not found sooner has to do with the remote region in which they grow. The area around Mt. Kilimanjaro has not received much attention from botanists in the past, having been overshadowed by the biodiverse Eastern Arc Mountains further south. 

Aside from discovering these trees, botanical surveys of Mt. Kilimanjaro are revealing this region to be just as biodiverse as the Eastern Arcs. Sadly, because of its long history of agriculture and more recent history of illegal logging, the rich forests of Mt. Kilimanjaro are quickly disappearing. The research team stresses the need to protect this area before one of Africa's biodiversity hotspots, as well as its tallest trees, are lost forever. 

Further Reading: [1]

Ancient Saw Palmettos in the Heart of Florida

When we think about long lived plants, our minds tend to fixate on bristlecone pines (Pinus longaeva), coastal redwoods (Sequoia sempervirens), or that clonal patch of quaking aspen (Populus tremuloides) in Utah. What would you say if I told you that we can add a palm tree to that list? Indeed, recent evidence suggests that the saw palmetto (Serenoa repens) can reach a ripe old age measured in thousands (yes, thousands) of years.

Now, at this point some of you are probably thinking "how can you measure the age of a palm when there are no annual growth rings?!" This is a legitimate hurdle that had to be overcome before such a claim was made. Using a lot of attention to detail and some crafty mathematics, a team of researchers was able to age saw palmettos in Florida's most ancient habitats.

This work was performed on a peculiar geological formation. Aptly named the "Mid-Florida Ridge," this 150 mile sand ridge bisects the middle of the state. Throughout much of the Pliocene and early Pleistocene, sea levels were as much as 50 meters higher than they were today. Nearly all of Florida was underwater during this time. All that stuck out above the water were a series of small islands. These islands served as refugia for flora and fauna pushed south by repeated glaciations. Once sea level receded to its current level, these islands were left high and dry, thus forming the ridge in question. Because of its history as a refugium, the Mid-Florida Ridge is home to a staggering array of plant species, some of which are endemic to this relatively small area of Florida.

Because of its relative stability through time, the Mid-Florida Ridge is a haven for long lived plant species. Thus, it was a prime location for trying to understand the longevity of the charismatic and ecologically important saw palmetto. By tagging individual palms and observing them year after year, researchers were able to get an idea of exactly how fast this species can grow. Depending on the soil conditions of the immediate area, saw palmettos grow at a rate of somewhere between 0.88 and 2.2 cm per year. They certainly aren't winning any speed races at that rate. Regardless, you can begin to see that an estimate of yearly growth rate can shine a light on how long these palms have been around. Measurements of tagged palmettos growing on the sand ridge show that individuals aged at a staggering 500 years are not uncommon!

This estimate gets a bit complicated when we consider another aspect of saw palmetto biology - they are clonal. For a variety of reasons, as saw palmettos grow, their sprawling stem will often branch out, creating clones of themselves. Over time, the trunk portions that connect these clones rot away, giving the impression that they are unique individuals. Genetic analyses showed that many of the palmettos in the study area were actually clones. Using some pretty sophisticated models coupled with their DNA evidence, the research team was able to reconstruct the growth history of many of these clones, thus allowing them to more accurately age these clonal colonies.

Their results are staggering to say the least. Based on the rate of growth and spread, the estimated age of these clonal patches of saw palmetto range anywhere between 1227–5215 years! At this point you should be asking yourself "how accurate are these data?" The truth is that the researchers were actually being quite conservative in their estimates. For instance, there were likely many clones well outside their study area. If so, they were likely underestimating the growth time of these clonal colonies. Additionally, they were only using the growth rates of adult saw palmettos in calculating average growth rates.

Seedling saw palmettos have been shown to have a reduced growth rate compared to adults, only 0.3 cm per year. Thus, they did not take into account the time it takes for seedlings to reach maturity. The team feel that accounting for such variables could increase the age estimates for such clonal patches to well over 8,000 years! I don't think we should be looking into buying that many birthday candles just yet, however, even their reported estimates are shocking to say the least.

What we can say is that for as long as Florida has been above water, saw palmettos have played an integral role in the ecology of the region. Long before humans began developing the state, the saw palmetto was functioning as a major player, shaping these sand ridge communities into the ecosystems they are today. It is without a doubt, a species worthy of our admiration and respect.

Further Reading: [1]

Tomatillos Just Got A Lot Older

Tomatillos and ground cherries just got a bit older. Okay, a lot older. Exquisitely preserved fossils from an ancient lake bed in Argentina are shining a very bright light on the genus Physalis and the family Solanaceae as a whole. Despite the importance of this plant family around the globe, little fossil evidence has ever been found. That is, until now. 

Dated at 52 million years old, these fossils paint a picture of a snapshot in the evolution of the genus Physalis. The fossils are remarkable, allowing for close inspection of minute details like vein structure. Because of the level of detail discernible, experts can say without a doubt that these fossils could be nothing else other than a species of Physalis

One of the most interesting aspects of these fossils is their age. These sediments were deposited during the early Eocene Epoch. The fact that representatives of Physalis were alive and well during this time is quite remarkable. Because fossil evidence for Solanaceae has been so scarce, experts have had to rely solely on molecular dating in order to elucidate the origin and divergence of this family. 

Original estimates placed the origin of Solanaceae at sometime around 30 million years before present. Physalis, being much more derived, was thought to have an even more recent emergence, some 9 million years ago. Boy, was that ever wrong. At 52 million years of age, we can now confidently say that Physalis is at least 43 million years older than previously thought. These findings also tell us that Solanaceae is even older still! If such a derived genus was thriving in Eocene Argentina 52 million years ago, basil members of the family must have gotten their start much earlier than we ever imagined. 

Aside from big picture taxonomical revelations, the fossils also give us a window into the ecology of these ancient Physalis. The most obvious is that inflated bladder which surrounds the berry within. Though it is quite characteristic of this group, little attention has been paid to its function. The fact that the sediments in which they were preserved are of aquatic origin suggests that the inflated calyces may have evolved for aquatic seed dispersal. Experiments have shown that these structures on modern day ground cherries and tomatillos do in fact float, keeping the berry inside high and dry. 

To think that all of this was brought to light from a handful of fossils. It just goes to show you the importance the paleontological discoveries can have. Just think of the countless amount of museum drawers and shelves that are chock full of interesting fossils waiting to be looked over. Who knows what they might tell us about our planet. 

Photo Credit: Ignacio Escapa, Museo Paleontológico Egidio Feruglio

Further Reading: [1]

Mayaca!

When I first saw this little plant growing along the boarders of a pond, I thought I was seeing a semiaquatic Lycopod. Was I ever wrong. It turns out I was looking at an angiosperm commonly encountered by aquarium enthusiasts - Mayaca fluviatilis. The genus Mayaca has its own family (Mayacaceae) and its members can be found throughout Southeastern North America, Latin America, the West Indies, and central Africa. It was very exciting to meet one of these plants in person!

Pseudoanthry

I learned a new word today - "pseudoanthery." This term applies to a structure or organ on a nectarless flower that mimics a dehiscent anther. To elaborate further, a dehiscent anther is one in which a capsule containing pollen breaks open to reveal the pollen inside. For example, think of the anthers of an Asiatic lily. Back to the topic at hand.

I quite like learning new things, especially as it applies to familiar friends. I was admiring the floral display of a rather tall cane begonia when a friend of mine came up to me and simply said "pseudoanthery." I didn't quite catch it the first time so I asked him to repeat it. It wasn't hard to guess the root meaning of the word - fake anther. Confusion set in when I pointed out that I was looking at the female flowers of a begonia. Thus, a teaching moment presented itself.

Though I adore Begonias and have a small handful growing in my house at all times, I never stopped to think much about their pollination. Without a doubt, they can be quite showy. Even the smaller species can put on quite a floral show. Rarely have I ever detected a scent from a Begonia bloom, nor have I ever detected nectar (though that's not to say either of those qualities don't exist). The point I am trying to make is that I couldn't quite figure out their strategy.

Sure, male flowers contain copious amounts of pollen. That is incentive enough to visit a male bloom. But what about the female flowers? Do they get away with not offering any sort of reward by simply being showy? Certainly that helps, however, female Begonia flowers sweeten the ruse with a bit of mimicry.

That is where the term pseudoanthery applies. Take a close look at the stigma of a begonia flower and you will be marveled by its intricate structure and bright coloration. As it turns out, the stigma is shaped in such a way as to mimic the pollen covered anthers of male flowers. Insects looking for protein rich pollen with visit the female flowers, realize it was all for naught, and move on. That is all the female flowers require. While the insect was busy searching for pollen, it is very likely that the bristly hairs on the stigma were able to pick up pollen grains from the insect's previous visit. With a little luck, that flower was a male begonia.

This ruse works best at large numbers. By producing lots of male flowers and considerably fewer female flowers, Begonias can ensure that the insects are not deterred by the lack of rewards. This has a double benefit for the plant as female flowers and seeds can be costly to produce.

Quite fascinating if I do say so myself. I have looked at countless Begonia flowers and not once did I question their structure. Just goes to show you that even old friends can teach us new things.

Further Reading: [1] [2]

A Peculiar Case of Bird Pollination

When we think of bird pollination, we often conjure images of a hummingbird sipping nectar from a long, tubular, red flower. Certainly the selection pressures brought about from entering into a pollination syndrome with birds has led to convergence in floral morphology across a wide array of different plant genera. Still, just when we think we have the natural world figured out, something new is discovered that adds more complexity into the mix. Nowhere is this more apparent than the peculiar relationship between an orchid and a bird native to South Africa.

The orchid in question is known scientifically as Disa chrysostachya. It is a bit of a black sheep of the genus. Whereas most Disa orchids produce a few large, showy flowers, this species produces a spike that is densely packed with minute flowers. They range from orange to red and, like most other bird pollinated flowers, produce no scent. 

Take the time to observe them in the field and you may notice that the malachite sunbird is a frequent visitor. The sunbirds perch themselves firmly on the spike and probe the shallow nectar spurs on each flower. At this point you may be thinking that the pollen sacs, or pollinia, of the orchid are affixed to the beak of the bird but, alas, you would be wrong. 

Closer inspection of the flowers reveal that the morphology and positioning of the pollinia are such that they simply cannot attach to the beak of the bird. The same goes for any potential insect visitors. The plant seems to have assured that only something quite specific can pick up the pollen. To see what is really going on, you would have to take a look at the sunbird's feet. 

That's right, feet. When a sunbird feeds at the flowers of D. chrysostachya, its feet position themselves onto the stiffened lower portion of the flower. This is the perfect spot to come into contact with the sticky pollinia. As the bird feeds, they pick up the pollinia on their claws! The next time the bird lands to feed, it will inevitably deposit that pollen. The orchids seemed to have benefited from the fact that once perched, sunbirds don't often reposition themselves on the flower spike. In this way, self pollination is minimized. A close relative, D. satyriopsis, has also appeared to enter into a pollination with sunbirds in a similar way. 

Though it may seem inefficient, research has shown that this pollination mechanism is quite successful for the orchid.The pollinia themselves stick quite strongly so that no amount of scuffing on branches or preening with beaks can dislodge them. Once pollination has been achieved, each flower is capable of producing thousands upon thousands of seeds.

Photo Credit: Johnson and Brown

Further Reading: [1]

A Shrub and Its Buffer Zone

Confession: I can be really bad at recognizing patterns. It's not my strong point. As such, I tend to remain skeptical of what I think I am seeing. Sometimes I am right, though. A recent stroke of luck came while I was hiking through some scrubby habitat in northern Florida. I walked out into a clearing to get a better view of a pond when I saw some interesting shrubs up on the banks. The area was largely covered in tufts of warm season grasses but the shrubs seemed to be ringed by barren, white sand. My botanist friend was kind enough to point out that the shrubs I was looking at were none other than sandhill rosemary (Ceratiola ericoides). With a name attached to these species, I could dive into the literature on this plant to see if I was actually seeing a true pattern or not.

Before we get to the meat of the article, it would be nice to first introduce you to the sandhill rosemary. C. ericoides is not a true rosemary at all. Its resemblance to the culinary mint is purely superficial. C. ericoides is a heath (family Ericaceae) and is the only member of its genus. It can be found growing in dry, scrubby habitats throughout southeastern North America. It is dioecious meaning each shrub is either male or female. Unlike its showier cousins, this heath is not pollinated by insects. Instead, it relies on wind. Because of this, C. ericoides flowers are highly reduced structures produced in the axils of leaves near the tips of its branches.

The scrubby habitats it calls home are challenging places for plants to live. The sandy soils drain water rapidly and are prone to shifting with the winds. The stout, needle like leaves are a fantastic adaptation for minimizing water loss during the hottest, driest months of the year. Also, regular fires are the norm. Burning is vital to the health of this region, however, C. ericoides does not seem to be very well adapted to cope with it. Instead, these shrubs are killed by fire, relying on the seed bank for regeneration. But that isn't the only thing this species has evolved in order to cope with a regular fire regime. As it turns out, C. ericoides may be utilizing chemical warfare to increase its chances of survival.

C. ericoides is what we call "allelopathic." Allelopathy can be defined as "the direct or indirect harmful or stimulatory effect of one plant on another through the production and release of chemical compounds" and is "an important form of plant-to-plant interference in natural and agricultural settings" (Rice 1984). In other words, allelopathic plants utilize chemicals that are toxic to other plants in order to gain an upper hand when it comes to acquiring space to grow. For C. ericoides, this may also mean keeping itself safe from fire.

As anyone who has tried to light a fire knows, a little fuel goes a long way. In the wild, plant materials make up the fuel load. The more plant material lying around, the more fuel the fire has to burn through. Much of the understory of these habitats are filled with fire adapted plant species. Grasses are possibly the most fire tolerant of them all. What's more, grasses often release specialized compounds when they burn that actually increase the temperature of the fire. This is often bad news for less fire adapted plants in the vicinity. If grasses and other fire adapted species were to be growing near C. ericoides, they would not only increase the chances of fire reaching the shrub but also increase the intensity of the flames. This is where the allelopathy comes in.

Evidence from greenhouse experiments has shown that the allelopathic compounds from C. ericoides inhibit the germination and growth of other plant species. This is especially true for fire adapted grasses. Although these chemicals are abundant in the leaves of C. ericoides, research also shows that they are produced in the roots as well. As the leaves fall off, they decompose and release their chemical cocktails into the soil immediately surrounding the shrub. This keeps plants at bay in the immediate vicinity while the roots go a bit further. Since the roots of C. ericoides branch outwards from the plant, the effectiveness of its chemical warfare is increased by a few meters radius around the shrub. Indeed, it is believed that C. ericoides is actually keeping the surrounding area clear of most fire adapted vegetation. In doing so, the shrubs are creating a fire-free buffer zone.

Although more work needs to be done in order to understand the degree to which these effects occur in the wild, this is nonetheless tantalizing evidence that such plant interactions are shaping the landscape in ways we don't fully understand. On a personal note, it was exciting to know that there really was something to the barren ring patterns I observed around each shrub.

Further Reading: [1] [2] [3]
 

Floral Deterrent

There is no mistaking the allure of certain floral scents. Entire industries have developed around capturing the essence of plant reproduction. Millions of years before we humans adopted floral scents for our own bidding, plants were producing them to attract pollinators. Even plants that produce sickening smells meant to mimic rotting flesh are trying to get the attention of something. It seems so obvious that these perfumes evolved as attractants but there are some plant species whose floral scents do the opposite. 

When I first caught a whiff of the blooms of the fragrant olive (Osmanthus fragrans) it didn't take long to track down its source. In my opinion it is one of the most enticing fragrances I have ever encountered. Native throughout much of Asia, this evergreen shrub produces sprays of tiny, pale, 4 lobed blossoms. Its attractive form and heavenly scent have led to its popularity in horticultural circles the world over. Surely its intense fragrance also makes it quite popular with pollinators. The truth is actually quite surprising.

In its native range, few insects seem to show it any attention. Aside from some hover flies, the list of floral visitors is surprisingly quite depauperate. What is going on? Why would this shrub go through the trouble of producing such volatile compounds? Has its intended pollinator gone extinct? Though it can be difficult to answer such inquiries, research done in Japan suggests that these scents may actually function as a deterrent rather than a lure. 

Researchers looked at a common butterfly species known to pollinate other flowering species in the area. The results of their experiments were quite shocking to say the least. Even when food was withheld for a period of time, the butterflies never visited the flowers of the fragrant olive. Only when the team replaced the flowers with replicas infused with a neutral scent did the butterflies pay them any attention. 

The fact that hover flies do in fact visit the flowers suggests that the scent compounds serve a dual function - attracting the intended pollinators while at the same time deterring potential nectar thieves. More work is needed before we can be completely confident in these conclusions but the idea nonetheless highlights the fact that more is going on with flowers than we realize. 

Photo Credit: hto2008 (http://bit.ly/2hPOhnO

Further Reading: [1]

The Lowly Lawn Orchid

A new year and a new orchid. It didn't take long for me to spot this little plant poking up between the succulent leaves of a potted aloe. My elation was short lived though. Alas, the sun was setting and I didn't have a flashlight or my camera. I was much luckier the next day. Actually, I shouldn't say lucky. This orchid isn't uncommon.

Meet the lawn orchid (Zeuxine strateumatica). Originally native to Asia, this species is expanding its range throughout many parts of the globe. Here in Florida, it was first discovered in 1936. There was a bit of confusion surrounding its origin on this continent, however, it is now believed that seeds arrived in a shipment of centipede-grass from China.

Since its premiere in Florida, the lawn orchid has since spread to Georgia, Alabama, and Texas. It seems to be quite tenacious, growing equally as well in lawns, floodplains, forests, meadows, and even sidewalk cracks! Despite this generalist habit, it does not seem to transplant well and is probably quite specific about its mycorrhizal partner. Much work needs to be done to sleuth out exactly why this little orchid has been able to spread so far outside of its native range.

Though small flies will visit the flowers, it is very likely that this orchid mostly self pollinates. It doesn't take long to flower and set seed. One plant can easily result in hundreds if not thousands of seedlings. After setting seed, the parent plant dies, however, it will often bud off new plantlets from its roots. Its ubiquitous nature can often stand in contrast to its ability to disappear for a series of time. Large stands that appear one year may not return for many years after. Still, in some areas this little orchid is abundant enough to be considered a nuisance.

Despite whatever feelings you may have towards this little plant, I nonetheless admire it. Its not often you find orchids so adaptable to a wide variety of conditions. At the very least it offers us insights into the success of plant invasions around the globe. And, in the end, its a nice looking little plant.

Further Reading: [1] [2]

A Primer on Trigger Plants

I would like to introduce you to another group of plants capable of abrupt movements. Whereas many species have evolved moving parts in order to capture prey or deter herbivores, the following genus moves as means of achieving pollination. Meet the genus Stylidium a.k.a. the trigger plants.

Native to parts of Asia and Australia, these beautiful little herbs are quite diverse, making generalizations difficult. Still, there is one thing they all share, a fused set of reproductive organs that lash out at unsuspecting pollinators. When a visiting insects of sufficient size lands on a flower, its weight causes a rapid change in turgor pressure within the column's tissues.

The rapid change in pressure sends the column flying. The position of this reproductive hammer varies from species to species. Some bash their pollinators on the back whereas others strike them under the abdomen. When the flowers first mature, only the male portions are mature. Thus, the initial visit dusts the insect with pollen. Once the pollen is gone, the column resets itself and the female portions start to mature. The next time an insect visits the bloom, the stigma will do the bashing. With any luck, the visiting insect will have already been dusted with pollen from a previous plant. In this way, the plant avoids self pollination.

Another morphological aspect shared among member of this genus is the production of glandular trichomes. These minute hairs cover the body of the plant and produce sticky mucilage that ensnares tiny insects. It was originally thought that this was a merely a defense mechanism that may represent a form of proto-carnivory.

However, analysis of the mucilage revealed that plant is also producing digestive enzymes capable of breaking down insects unfortunate enough to have been caught. It remains to see whether or not the plants absorb nutrients in the same way as sundews but the fact that these plants share the same nutrient-poor habitats as many other Australian carnivores lends some credibility.

Photo Credit: http://bit.ly/2hJjMyc and Francis Nge

Further Reading: [1] [2]

The Ant-Farming Tillandsias

Tillandsias are all the rage. Their relative ease of care has found them included in seemingly every terrarium sold these days; often in very inappropriate circumstances that result in their death. There is no denying that these epiphytic relatives of the pineapple are unique and beautiful plants but I would argue that their ecology is probably the coolest aspect about them. I am particularly fond of the bulbous species because of their relationship with ants.

That's right, there are upwards of 13 species of bulbous Tillandsia that offer up housing for ants. If you look closely at the leaves of these species, you will notice that they roll up to form tubes that lead down into the bulb at the base. The space between the leaves forms a hollow chamber, functioning as a perfect microclimate for ants to nest. In many habitats, these Tillandsia offer better housing than the surrounding environment. One would be surprised at how many ants can fit in there too. Colonies containing anywhere between 100 - 300 ants are not unheard of.

The rewards for the plant are obvious. Ants provide nutrients as well as protection. In return the ants get a relatively safe and dry place to live. Ant domatia have been recorded in roughly 13 different species, many of which are some of the most commonly sold Tillandsias on the market such as T. baileyi, T. balbisiana, T. bulbosa, and T. caput-medusae. If this doesn't make your hanging glass Tillandsia orb even cooler then I don't know what will.

Photo Credits: scott.zona (http://bit.ly/16kZ1RR) and Alex Popovkin (http://bit.ly/1BXMEUH)

Further Reading: [1] [2]

Important Lessons From Ascension Island

Located in the middle of the South Atlantic, Ascension Island is probably not on the top of anyone's travel list. This bleak volcanic island doesn't have much to offer the casual tourist but what it lacks in amenities it makes up for in a rich and bizarre history. Situated about 2,200 km east of Brazil and 3,200 km west of Angola, this remote island is home to one of the most remarkable ecological experiments that is rarely talked about. The roots of this experiment stem back to a peculiar time in history and the results have so much to teach the human species about botany, climate, extinction, speciation, and much more. What follows is not a complete story; far from it actually. However, my hope is that you can take away some lessons from this and, at the very least, use it as a jumping off point for future discussions. 

Ascension Island is, as land masses go, quite young. It arose from the ocean floor a mere 1 million years ago and is the result of intense volcanic activity. Estimates suggest that volcanism was still shaping this island as little as 1000 years ago. Its volcanic birth, young age, isolated conditions, and nearly non-existent soils meant that for most of its existence, Ascension Island was a depauperate place. It was essentially a desert island. Early sailors saw it as little more than a stopover point to gather turtles and birds to eat as they sailed on to other regions. It wasn't until 1815 that any permanent settlements were erected on Ascension. 

In looking for an inescapable place to imprison Napoleon Bonaparte, the Royal Navy claimed Ascension in the name of King George III. Because Napoleon had a penchant for being an escape artist, the British decided to build a garrison on the island in order to make sure Napoleon would not be rescued. In doing so, the limitations of the island quickly became apparent. There were scant soils in which to grow vegetables and fresh water was nearly nonexistent. 

The native flora of Ascension was minimal. It is estimated that, until the island was settled, only about 25 to 30 plant species grew on the island. Of those 10 (2 grasses, 2 shrubs, and 6 ferns) were considered endemic. If the garrison was to persist, something had to be done. Thus, the Green Mountain garden was established. British marines planted this garden at an elevation of roughly 2000 feet. Here the thin soils supported a handful of different fruits and vegetables. In 1836, Ascension was visited by a man named Charles Darwin. Darwin took note of the farm that had developed and, although he admired the work that was done in making Ascension "livable" he also noted that the island was "destitute of trees."

One of Ascension Island's endemic ferns - Pteris adscensionis

One of Ascension Island's endemic ferns - Pteris adscensionis

Others shared Darwin's sentiment. The prevailing view of this time period was that any land owned by the British empire must be transformed to support people. Thus, the wheels of 'progress' turned ever forward. Not long after Darwin's visit, a botanist by the name of Joseph Hooker paid a visit to Ascension. Hooker, who was a fan of Darwin's work, shared his sentiments on the paucity of vegetation on the island. Hooker was able to convince the British navy that vegetating the island would capture rain and improve the soil. With the support of Kew Gardens, this is exactly what happened. Thus began the terraforming of Green Mountain.

For about a decade, Kew shipped something to the tune of 330 different species of plants to be planted on Ascension Island. The plants were specifically chosen to withstand the harsh conditions of life on this volcanic desert in the middle of the South Atlantic. It is estimated that 5,000 trees were planted on the island between 1860 and 1870. Most of these species came from places like Argentina and South Africa. Soon, more plants and seeds from botanical gardens in London and Cape Town were added to the mix. The most incredible terraforming experiment in the world was underway on this tiny volcanic rock. 

By the late 1870's it was clear the the experiment was working. Trees like Norfolk pines (Araucaria heterophylla), Eucalyptus spp. and figs (Ficus spp.), as well as different species of banana and bamboo had established themselves along the slopes of Green Mountain. Where there was once little more than a few species of grass, there was now the start of a lush cloud forest. The vegetation community wasn't the only thing that started to change on Ascension. Along with it changed the climate. 

Estimates of rainfall prior to these terraforming efforts are sparse at best. What we have to go on are anecdotes and notes written down by early sailors and visitors. These reports, however, paint a picture of astounding change. Before terraforming began, it was said that few if any clouds ever passed overhead and rain rarely fell. Those living on the island during the decade or so of planting attested to the fact that as vegetation began to establish, the climate of the island began to change. One of the greatest changes was the rain. Settlers on the island noticed that rain storms were becoming more frequent. Also, as one captain noted "seldom more than a day passes over now without a shower or mist on the mountain." The development of forests on Ascension were causing a shift in the island's water cycle. 

Plants are essentially living straws. Water taken up by the roots travels through their tissues eventually evaporating from their leaves. The increase in plant life on the island was putting more moisture into the air. The humid microclimate of the forest understory cooled the surrounding landscape. Water that would once have evaporated was now lingering. Pools were beginning to form as developed soils retained additional moisture.

Now, if you are anything like me, at this point you must be thinking to yourself "but what about the native flora?!" You have every right to be concerned. I don't want to paint the picture that everything was fine and dandy on Ascension Island. It wasn't. Even before the terraforming experiment began, humans and other trespassers left their mark on the local biota. With humans inevitably comes animals like goats, donkeys, pigs, and rats. These voracious mammals went to work on the local vegetation. The early ecology that was starting to develop on Ascension was rocked by these animals. Things were only made worse when the planting began.

Of the 10 endemic plants native to Ascension Island, 3 went extinct, having been pushed out by all of the now invasive plant species brought to the island. Another endemic, the Ascension Island parsley fern (Anogramma ascensionis) was thought to be extinct until four plants were discovered in 2010. The native flora of Ascension island was, for the most part, marginalized by the introduction of so many invasive species. This fact was not lost of Joseph Hooker. He eventually came to regret his ignorance to the impacts terraforming would have on the native vegetation stating “The consequences to the native vegetation of the peak will, I fear, be fatal, and especially to the rich carpet of ferns that clothed the top of the mountain when I visited it." Still, some plants have adapted to life among their new neighbors. Many of the ferns that once grew terrestrially, can now be found growing epiphytically among the introduced trees on Green Mountain. 

The Ascension Island parsley fern (Anogramma ascensionis)

The Ascension Island parsley fern (Anogramma ascensionis)

Today Ascension Island exists as a quandary for conservation ecologists. On the one hand the effort to protect and conserve the native flora and fauna of the island is of top priority. On the other hand, the existence of possibly the greatest terraforming effort in the world begs for ecological research and understanding. A balance must be sought if both goals are to be met. Much effort is being put forth to control invasive vegetation that is getting out of hand. For instance, the relatively recent introduction of a type of mesquite called the Mexican thorn (Prosopis juliflora) threatens the breeding habitat of the green sea turtle. Efforts to remove this aggressive species are now underway. Although it is far too late to reverse what has been done to Ascension Island, it nonetheless offers us something else that may be more important in the long run: perspective.

If anything, Ascension Island stands as a perfect example of the role plants play in regulating climate. The introduction of these 330+ plant species to Ascension Island and the subsequent development of a forest was enough to completely change the weather of that region. Where there was once a volcanic desert there is a now a cloud forest. With that forest came clouds and rain. If adding plants to an island can change the climate this much, imagine what the loss of plants from habitats around the world is doing. 

Each year an estimated 18 million acres of forest are lost from this planet. As human populations continue to rise, that number is only going to get bigger. It is woefully ignorant to assume that habitat destruction isn't having an influence on global climate. It is. Plants are habitat and when they go, so does pretty much everything else we hold near and dear (not to mention require for survival). If the story of Ascension does anything, I hope it serves as a reminder of the important role plants play in the function of the ecosystems of our planet. 

The endemic Ascension spurge (Euphorbia origanoides)

The endemic Ascension spurge (Euphorbia origanoides)

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

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

 

A Cave Dwelling Nettle From China

Caves and plants do not seem like a good combo. Plants need sunlight and caves offer very little to none of it. However, plants in general never seem to read the literature we write about them. As such, they are constantly surprising botanists all over the world. 

A recent example of this was published back in September of 2012. A team of botanists exploring limestone gorges in southwestern China stumbled upon three new members of the nettle family. One of these nettles seemed to be right at home growing well within two limestone caves. 

Needless to say this was quite a shock to the botanists. The regions in which these plants were growing were quite dim, with light levels ranging from a mere 0.04% to a measly 2.78 % of full daylight! Although this is by no means complete darkness, it is an incredibly low amount of sunlight for a plant that still relies on photosynthesis to get by. 

They named the nettle Pilea cavernicola in reference to its cave-dwelling habit. While it has only just been discovered, the IUCN considers this species vulnerable. Only two populations are known and their proximity to expanding human activity puts them in danger of rapid extinction. 

Photo Credit: Monro & Wei

Further Reading: [1]