Path Rush

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Path rush (Juncus tenuis) is one of those plants that has really benefited from human expansion. Originally native to North America, it can now be found in numerous countries around the globe. It owes much of its success to both its ability to tolerate lots of disturbance as well as an ingenious seed dispersal mechanism. If you like to hike, there is a good chance you have encountered path rush somewhere along the way. There is also a strong chance that you have dispersed its seeds.

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Path rush is a relatively small species, topping out around 60 cm in height. Because it frequently grows where foot traffic is heavy, plants don’t always reach such stature. Like most rushes, it has round stems and surprisingly attractive flowers, though one would need a hand lens to fully appreciate their beauty. Flowering for path rush occurs during the summer and it is thought that wind is the main pollination mechanism for this species.

The darker vegetation running along the path is all path rush!

The darker vegetation running along the path is all path rush!

Following pollination, each flower is replaced by a tiny capsule filled with tiny seeds. Each seed is covered in a substance that turns into a sticky mucilage when wet. This mucilage is how path rush manages to move around the landscape so easily. The sticky seeds glom onto pretty much everything from fur to feathers, boots to car tires. This is why you most often find path rush on, well, paths! Its sticky seeds are carried far and wide by foot traffic. It is also why you can now find path rush growing well outside of North America.

Path rush enjoying a crack in the sidewalk.

Path rush enjoying a crack in the sidewalk.

Path rush frequents more habitats than simply paths too. The key to its success is soil disturbance. Anywhere the soil has been compacted and disturbed, path rush can find its niche. With little competition from surrounding vegetation, this tiny rush can grow into impressive colonies. Even cracks in asphalt can harbor a plant or two. Aside from its ability to tolerate soil disturbance, its tough, stringy foliage is not fed on by a lot of herbivores, which gives it yet another leg up on potential competitors. All in all, this is one tough little plant.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2]



Trout Lily Appreciation

This video is a celebration of the white trout lily (Erythronium albidum) and its various spring ephemeral neighbors. We even talk about the threat that invasive species like garlic mustard (Alliara petiolata).

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

Music by
Artist: Botanist
Track:
https://verdant-realm-botanist.bandcamp.com/

An Ancient Hawaiian Moss

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The cloud forests of Kohala Mountain on the island of Hawai'i are home to a unique  botanical community. One plant in particular is quite special as it may be one of the most ancient clonal organisms in existence. Look down at your feet and you may find yourself surrounded by a species of moss known as Sphagnum palustre. Although this species enjoys a broad distribution throughout the northern hemisphere, its presence on this remote volcanic island is worth closer inspection. 

Hawai'i is rather depauperate in Sphagnum representatives and those that have managed to get to this archipelago are often restricted to growing in narrow habitable zones between 900 to 1,900 meters in elevation as these are the only spots that are cool and wet enough to support Sphagnum growth. Needless to say, successful colonization of the Hawaiian Islands by Sphagnum has been a rare event.  The fact that Sphagnum palustre was one of the few that did should not come as any surprise. What should surprise you, however, is how this particular species has managed to persist. 

Mounds of  S. palustre  in its native habitat. 

Mounds of S. palustre in its native habitat. 

Hawaiian moss aficionados have long noted that the entire population of Kohala's S. palustre mats never seem to produce a single female individual. Indeed, this moss is dioicous, meaning individuals are either male or female. As such, many have suspected that the mats of S. palustre growing on Kohala represented a single male individual that has been growing vegetatively ever since it arrived as a spore on the island. The question then becomes, how long has this S. palustre individual been on Kohala?

To answer that, researchers decided to take a look at its DNA. What they discovered was surprising in many ways. For starters, all plants were in fact males of a single individual. A rare genetic trait was found in the DNA of every population they sampled. This trait is so rare that the odds of it turning up in any number by sheer chance is infinitesimally small. What this means is that every S. palustre population found on Kohala is a clone of a single spore that landed on the mountain at some point in the distant past. Exactly how distant was the next question the team wanted to answer. 

A lush cloud forest on the slopes of Kohala.

A lush cloud forest on the slopes of Kohala.

The first clue to this mystery came from peat deposits found on the slopes of the mountain. Researchers found remains of S. palustre in peat deposits that were dated to somewhere around 24,000 years old. So, it would appear that S. palustre has been growing on Kohala since at least the late Pleistocene. But how long before that time did this moss arrive?

Again, DNA was the key to unlocking this mystery. By studying the rate at which mutations arise and fix themselves within the genetic code of this plant, they were able to estimate the average rate of mutation through time. By sampling different moss populations on Kohala, they could then use those estimates to figure out just how long each mat has been growing. Their estimates suggest that the ancestral male sport arrived on Hawai'i somewhere between 49,000 and 50,000 years ago and it has been cloning itself ever since. 

A large mat of  S. palustre

A large mat of S. palustre

As if that wasn't remarkable in and of itself, their thorough analysis of the genetic diversity within S. palustre revealed a remarkable amount of genetic diversity for a clonal organism. Though not all genetic mutations are beneficial, enough of them have managed to fix themselves into the DNA of the moss clones over thousands of years. The DNA of S. palustre is challenging long-held assumptions about genetic diversity of asexual organisms.

Of course, no conversation about Hawaiian botany would be complete without mention of invasive species. As one can expect at this point, Kohala's S. palustre populations are being crowded out by more aggressive vegetation introduced from elsewhere in the world. Unlike a lot of Hawaiian plants, however, the clonal habit of S. palustre puts a more nuanced twist to this story. 

Because Sphagnum is spongy yet durable, it has often been used as packing material. Packages stuffed with S. palustre from Kohala have been sent all over the island and because of this, S. palustre is now showing up en masse on other islands in the archipelago. Sadly, when it starts to grow in habitats that have never experienced the ecosystem engineering traits of a Sphagnum  moss, S. palustre gets pretty out of hand. It's not just packages that spread it either. All it takes is one sprig of the moss stuck on someone's boot to start a new colony elsewhere. The unique flora elsewhere in the Hawaiian archipelago have not evolved to compete with S. palustre and as a result, escaped populations are rapidly changing the ecology to the detriment of other endemic Hawaiian plants. 

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] 

California Bumblebee Decline Linked to Feral Honeybees

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Worldwide, pollinators are having a rough go of it. Humans have altered the landscape to such a degree that many species simply can't keep up. The proverbial poster child for pollinator issues is the honeybee (Apis mellifera). As a result, countless native pollinators get the short shrift when it comes to media attention. This isn't good because outside of intense industrial agriculture, native pollinators make up the bulk of pollination services. Similarly, honeybee fandom often overshadows any potential negative effects these introduced insects might be having on native pollinators.

Long term scientific investigations are starting to paint a more nuanced picture of the impact introduced honeybees are having on native ecosystems. For instance, research based out of California is finding that honeybees are playing a big role in the decline of native bumblebee populations. What's more, these negative impacts are only made worse in the light of climate change.

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For over 15 years, ecologist Dr. Diane Thompson has been studying bumblebee populations in central California. At no point during those early years did any of the bumblebee species she focuses on show signs of decline. In fact, they were quite common. Then, around the year 2000, feral honeybees started to establish themselves in the area. Honeybee colonies were becoming more and more numerous each and every year and that is when she started noticing changes in bumblebee behavior and numbers.

You see, honeybees are extremely successful foragers. They are generalists, which means they can visit a wide variety of flower types. As a result, they are extremely good at competing for floral resources compared to native bumblebees. Her results show that increases in the number of honeybee colonies caused not only a reduction in foraging among the native bumblebees, they also caused a reduction in bumblebee colony success. The native bumblebees simply weren't raising as many young as they were before honeybees entered the system.

Decreased rainfall cause a decline in flower densities of  Scrophularia californica , a key resource for native bumblebees in this system.

Decreased rainfall cause a decline in flower densities of Scrophularia californica, a key resource for native bumblebees in this system.

Climate change is only making things worse. As drought years become not only more severe but also more intense, the amount of flowers available during the growing season also declines. With fewer flowers on the landscape, bumblebees and honeybees are forced into closer proximity for foraging and the clear winner in most foraging disputes are the tenacious honeybees. As such, bumblebees are chased off the already diminishing floral displays. By 2014, Dr. Thompson had quantified a significant decline in native bumblebee populations as a result.

It would be all too convenient to say that this research represents an isolated case. It does not. More and more research is finding that honeybees frequently out-compete native pollinators for resources such as food and nesting sites. Such effects are especially pronounced in rapidly changing ecosystems. Although honeybees are here to stay, it is important that we realize the impacts that these feral insects are having on our native ecosystems and begin to better appreciate and facilitate the services provided by our native pollinators. 

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

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

Ferns Afloat

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My introduction to the genus Salvinia was as an oddball aquarium plant floating in a display tank at the local pet store. I knew nothing about plants at the time but I found it to be rather charming nonetheless. Every time the green raft of leaves floated under the filter outlet, water droplets would bead off them like water off of a ducks back. Even more attractive were the upside down forest of "roots" which were actively sheltering a bunch of baby guppies. 

I grew some Salvinia for a few years before my interest in maintaining aquariums faded. I had forgotten about them for quite some time. Much later as I was diving into the wild world of botany, I started revisiting some of the plants that I had grown in various aquariums to learn more about them. It wasn't long before the memory of Salvinia returned. A quick search revealed something astonishing. Salvinia are not flowering plants. They are ferns! 

The genus Salvinia is wide spread. They can be found growing naturally throughout North, Central, and South America, the West Indies, Europe, Africa, and Madagascar. Sadly, because of their popularity as aquarium and pond plants, a few species have become extremely aggressive invaders in many water ways. More on that in a bit. 

Salvinia comprises roughly 12 different species. Of these, at least 4 are suspected to be naturally occurring hybrids. As you have probably already gathered, these ferns live out their entire lives as floating aquatic plants. Their most obvious feature are the pairs of fuzzy green leaves borne on tiny branching stems. These leaves are covered in trichomes that repel water, thus keeping them dry despite their aquatic habit. 

These are not roots!

These are not roots!

Less obvious are the other types of leaves these ferns produce. What looks like roots dangling below the water's surface are actually highly specialized, finely dissected leaves! I was super shocked to learn this and to be honest, it makes me appreciate these odd little ferns even more. It is on those underwater leaves that the spores are produced. Specialized structures called sporocarps form like tiny nodules on the tips of the leaf hairs.

Sporocarps come in two sizes, each producing its own kind of spore. Large sporocarps produce megaspores while the smaller sporocarps produce microspores. This reproductive strategy is called heterospory. Microspores germinate into gametophytes containing male sex organs or "antheridia," whereas the megaspores develop into gametophytes containing female sex organs or "archegonia." 

As I mentioned above, some species of Salvinia have become aggressive invaders, especially in tropical and sub-tropical water ways. Original introductions were likely via plants released from aquariums and ponds but their small spores and vegetative growth habit means new introductions occur all too easily. Left unchecked, invasive Salvinia can form impenetrable mats that completely cover entire bodies of water and can be upwards of 2 feet thick!

Sporocarps galore! 

Sporocarps galore! 

Lots of work has been done to find a cost effective way to control invasive Salvinia populations. A tiny weevil known scientifically as Cyrtobagous singularis has been used with great success in places like Australia. Still, the best way to fight invasive species is to prevent them from spreading into new areas. Check your boots, check your boats, and never ever dump your aquarium or pond plants into local water ways. Provided you pay attention, Salvinia are rather fascinating plants that really break the mold as far as most ferns are concerned. 

Photo Credits: [1] [2] [3]

Further Reading: [1] [2] [3]

 

This Isn't Even My Final Form! A Pothos Story

Pothos might be one of the most widely cultivated plants in modern history. These vining aroids are so common that I don't think I can name a single person in my life that hasn't had one in their house at some point or another. Renowned for their hardy disposition and ability to handle extremely low light conditions, they have become famous the world over. They are so common that it is all too easy to forget that they have a wild origin. What's more, few of us ever get to see a mature specimen. The plants living in our homes and offices are mere juveniles, struggling to hang on as they search for a canopy that isn't there.

Trying to find information on the progenitors of these ubiquitous houseplants can be a bit confusing. To do so, one must figure out which species they are talking about. Without a proper scientific name, it is nearly impossible to know which plant to refer to. Common names aside, pothos have also undergone a lot of taxonomic revisions since their introduction to the scientific community. Also, what was thought to be a single species is actually a couple.

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To start with, the plants you have growing in your home are no longer considered Pothos. The genus Pothos seemed to be a dumping ground for a lot of nondescript aroid vines throughout the last century. Many species were placed there until proper materials were thoroughly scrutinized. Today, what we know as a "Pothos" has been moved into the genus Epipremnum. This revision did not put all controversies to rest, however, as the morphological changes these plants go through as they age can make things quite tricky.

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As I mentioned, the plants we keep in our homes are still in their juvenile form. Like all plants, these vines start out small. When they find a solid structure in a decent location, they make their bid for the canopy. Up in a tree in reach of life giving sunlight, these vines really hit their stride. They quickly grow their own version of a canopy that consists of massive leaves nearing 2 feet in length! This is when these plants begin to flower. 

As is typical for the family, the inflorescence consists of a spadix covered by a leafy spathe. The spadix itself is covered in minute flowers and these are the key to properly identifying species. When pothos first made its way into the hands of botanists, all they had to go on were the small, juvenile leaves. This is why their taxonomy had been such a mess for so long. Materials obtained in 1880 were originally named Pothos aureus. It was then moved into the genus Scindapsus in 1908.

Controversy surrounding a proper generic placement continued throughout the 1900's. Then, in the early 1960's, an aroid expert was finally able to get their hands on an inflorescence. By 1964, it was established that these plants did indeed belong in the genus Epipremnum. Sadly, confusion did not end there. The plasticity in forms and colors these vines exhibit left many confusing a handful of species within the group. At various times since the late 1960's, E. aureum and E. pinnatum have been considered two forms of the same species as well as two distinct species. The latest evidence I am aware of is that these two vines are in fact distinct enough to warrant species status. 

The plant we most often encounter is E. aureum. Its long history of following humans wherever they go has led to it becoming an aggressive invader throughout many regions of the world. It is considered a noxious weed in places like Australia, Southeast Asia, India, Pakistan, and Hawai'i (just to name a few). It does so well in these places that it has been a little difficult to figure out where these plants originated. Thanks to some solid detective work, E. aureum is now believed to be native to Mo'orea Island off the west coast of French Polynesia. 

Epipremnum pinnatum  is similar until you see an adult plant

Epipremnum pinnatum is similar until you see an adult plant

It is unlikely that most folks have what it takes to grow this species to its full potential in their home. They are simply too large and require ample sunlight, nutrients, and humidity to hit their stride. Nonetheless there is something to be said for the familiarity we have with these plants. They have managed to enthrall us just enough to be a fixture in so many homes, offices, and shopping centers. It has also helped them conquer far more than the tiny Pacific island on which they evolved. Becoming an invasive species always seems to have a strong human element and this aroid is the perfect example.

Photo Credits: [1] [2] [3] [4]

Further Reading: [1] [2] [3] 

 

Understanding the Cocklebur

Spend enough time in disturbed areas and you will certainly cross paths with a cocklebur (Xanthium strumarium). As anyone with a dog can tell you, this plant has no problems getting around. It is such a common occurrence in my life that I honestly never stopped long enough to think about its place on the taxonomic tree. I always assumed it was 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. 

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]

The Flowering Rush

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

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

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

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

Photo Credit: [1] [2]

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

The Enemy of My Enemy is My Friend

Spotted Knapweed (Centaurea maculosa)

Spotted Knapweed (Centaurea maculosa)

Plants produce a lot of chemicals. I mean a lot. Some of these are involved in day to day functions like growth and reproduction. The function of others can be a bit less obvious. These are often referred to as secondary compounds as they are not directly involved in growth or reproduction. Some of these chemicals are toxic to other plants. We call these compounds allelochemicals. Producing allelochemicals can give some plants a competitive advantage by knocking back their neighbors. However, like most things in ecology, this situation isn't always that simple. 

Take the example of spotted knapweed (Centaurea maculosa). This nasty invader is wreaking havoc on plant communities throughout western North America. It wages its war under the soil where it releases a chemical from its roots called "catechin." This chemicla kills native plants, especially native grasses growing nearby. This competitive advantage can lead to total dominance of spotted knapweed in many areas where it quickly rises to monoculture status. 

Silky lupine (Lupinus sericeus)

Silky lupine (Lupinus sericeus)

Not all native plants are equally susceptible to spotted knapweeds effects. Two native forbs stand out above the rest in being able to cope with the allelochemicals released by spotted knapweed. Enter silky lupine (Lupinus sericeus) and blanketflower (Gaillardia grandiflora). Where these plants occur alongside spotted knapweed, other natives seem to do a bit better. This made researchers curious. What was it about these two species?

Blanketflower (Gaillardia grandiflora)

Blanketflower (Gaillardia grandiflora)

As it turns out, both of these natives secrete their own chemicals. These don't act as allelochemicals though. Instead, it was found that they neutralize the detrimental effects of the catechin. In doing so, both the lupine and the blanketflower create a safe zone for other natives to reestablish. This could be good news as it hints at new ways of approaching certain plant invasions. More work needs to be done to see how well this situation plays out in a natural setting but the evidence is tantilizing to say the least!

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

Further Reading: [1]

Early Spring Botanizing

SURPRISE!

Many have commented that a video component was lacking from the hiking podcasts. I have teamed up with filmmaker/producer Grant Czadzeck (www.grantczadzeck.com) to bring you a visual botanizing experience. I'm not sure how regular this will become but let us know what you think. In the mean time, please enjoy this early spring hike in central Illinois.

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]

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]

 

Floating Ferns

Not every tiny plant you see growing on the surface of ponds are duckweeds. Sometimes they are Azolla. Believe it or not, these are tiny, floating ferns! The genus Azolla is comprised of about 7 to 11 different species, all of which are aquatic. Despite being quite small they nonetheless exert a massive influence wherever they grow. 

Like all ferns, Azolla reproduce via spores. Unlike more familiar ferns, however, sexual reproduction in Azolla consists of two markedly different types of spores. When conditions are right, little structures called "sporocarps" are formed underneath the branches. These produce one of two types of sporangia. Male sporangia are small and are often referred to as microspores whereas female sporangia are, relatively speaking, quite large and are referred to as megaspores. The resulting gametophytes develop within and never truly leave their respective spores. Instead, male gameotphytes release motile sperm into the water column and female gametophytes peak out of the megaspore to intercept them. Thus, fertilization is achieved. 

Azolla are fast growing plants. Via asexual reproduction, these little floating ferns can double their biomass every 3 to 10 days. That is a lot of plant matter in a short amount of time. As such, entire water bodies quickly become smothered by a fuzzy-looking carpet. Depending on the species and the environmental conditions, the color of this carpet can range from deep green to nearly burgundy. They are able to float because of their overlapping scale-like leaves, which trap air. Below each plant hangs a set of roots. The roots themselves form a symbiotic relationship with a type of cyanobacterium, which fixes atmospheric nitrogen. Couple with their astronomic growth rate, this means that colonies of Azolla quickly reach epic proportions.

In fact, they can grow so fast that Azolla may have played a serious role in a massive global cooling event that occurred some 50 million years ago. During that time, Earth was much warmer than it is now. Global temperatures were so warm that tropical species such as palms grew all the way into the Arctic. There is fossil evidence that massive blooms of Azolla may have occurred in the Arctic Ocean during this time, which was a lot less saline than it is now.

Everything red in this picture is  Azolla .

Everything red in this picture is Azolla.

Though plenty of other factors undoubtedly played a role, it is believed that Azolla blooms would have been so large that they would have drawn down CO2 levels considerably over thousands of years. As these blooms died they sank to the sea floor, bringing with them all of the carbon they had locked up in their cells. In part, this may have led to a massive drop in atmospheric CO2 levels and led to a subsequent cooling period. Evidence for this is tantalizing, so much so that some researchers have taken to calling this "The Azolla Event." However, this is far from a smoking gun. Regardless, it is an important reminder than really big things often come in very small packages.

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

Further Reading: [1] [2]

 

The Amazing Radiation of Hawaii's Lobeliads

Hawai'i is home to so many interesting species of plants, many of which are found nowhere else in the world. One group, however, stands out among the rest in that it represents the largest plant radiation not just in Hawai'i but on any island archipelago in the world!

I am of course talking about the Hawaiian lobelioids. We are familiar with species found on North America, which include the lovely cardinal flower (Lobelia cardinalis) and the great blue lobelia (Lobelia siphilitica), but the 6 genera that comprise the Hawaiian radiation are something quite different altogether.

Numbering roughly 125 species in total (and many extinct species as well), it was long thought that they were the result of at least 3 separate invasions. Thanks to recent DNA analysis, it is now believed that all 6 genera are the result of one single invasion by a lobelia-like ancestor. This may seem ridiculous but, when you consider the fact that this invasion happened back when Gardner Pinnacles and French Frigate Shoals were actual islands and none of the extant islands were even in existence, then you can kind of grasp the time scales involved that produced such a drastic and varied radiation.

Sadly, like countless Hawaiian endemics, the invasion of the human species has spelled disaster. Hawaiian endemics are declining at an alarming rate. Introduced pigs and rats eat seeds, devour seedlings, and even go as far as to chew right through the stems of adult plants. To make matters worse, many species evolved to a specific suite of pollinators. Take the genus Clermontia for example. The flowers of these species are evolved for pollination by the island's endemic honey creepers. Due to avian malaria and other human impacts, many honey creepers are endangered and some have already gone extinct. Without their pollinators, many of these lobelioids are doomed to slow extinction if they haven't disappeared already. For some, what few populations remain are now fenced off and have to be hand pollinated. As I have said all too often, the future of this great radiation of plants is uncertain.

Photo Credits: Oakapples (http://bit.ly/OjOqhU), Forest and Kim Starr (http://bit.ly/1miCAA5), Dave Janas

Further Reading:

http://bit.ly/2aIviF5

http://bit.ly/2bh9Dpv

http://bit.ly/2b4i5dV

The Fall of Corncockle

This switch from more traditional farming practices to industrialized monocultures has left a damaging legacy on ecosystems around the globe. This is especially true for unwanted plants. Species that once grew in profusion are now sprayed and tilled out of existence. Nowhere has this been better illustrated than for a lovely little plant known commonly as the corncockle (Agrostemma githago). 

This species was once a common weed in European wheat fields. Throughout much of the 19th and early 20th century, it was likely that most wheat sold contained a measurable level of corncockle seed. Its pink flowers would have juxtaposed heavily against the amber hue of grain. Indeed, its habit of associating with wheat has lead to its introduction around the globe. It can now be found growing throughout parts of North America, Australia, and New Zealand. 

However, in its home range of Europe, the corncockle isn't doing so well. The industrialization of farming dealt a huge blow to corncockle ecology. The broad-scale application of herbicides wreaked havoc on corncockle populations. Much more detrimental was the switch to winter wheat, which caused a decoupling between harvest time and seed set for the corncockle. Whereas it once synced quite nicely with regular wheat harvest, winter wheat is harvested before corncockle can set seed. As such, corncockle has become extremely rare throughout its native range and was even thought to be extinct in the UK. 

A discovery in 2014 changed all of that. National Trust assistant ranger Dougie Holden found a single plant flowering near a lighthouse. Extensive use of field guides and keys confirmed that this plant was indeed a corncockle, the first seen blooming in the UK in many decades. It is likely that the sole plant grew from seed churned up by vehicle traffic the season before. 

Photo Credit: sonnentau (bit.ly/1qo3XQK)

Further Reading:
Clapham, A.R., Tutin, T.G. and Warburg, E.F. 1968. Excursion Flora of the British Isles. Cambridge University Press