Celebrating the Forked Spleenwort

What can I say, I am a total sucker for ferns with "untraditional" fronds. Whereas the tropics offer seemingly endless fern varieties, I find that there is something special about temperate ferns that, for lack of a better phrase, break the mold. I was recently introduced to such a fern. Known commonly as the forked spleenwort, Asplenium septentrionale looks more like a clump of grass than it does a fern.

A closer inspection, however, would reveal that it is indeed a Pteridophyte. It grows on rocky outcrops, including stone walls, throughout the northern hemisphere. Here in North America, it is predominantly found in the Rocky Mountains. It is a small fern that often forms dense clusters in cracks and crevices. Its stems are long, narrow, and grass-like, ending in a flattened leaf blade that often forks at the tip. In typical fractal fashion, these leaf blades fork again at the tips, forming minute pinnae.

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The forked spleenwort has gone through considerable taxonomic revisions since it was first described by Linnaeus in 1753. Originally it was named Acrostichum septentrionale, but was then moved into Asplenium a few decades later. Renewed interest in this species during the mid 20th century saw the forked spleenwort moved to the genus Chamaefilix followed by Tarachia, though these did not gain much scientific credence. As such, it has remained an Asplenium ever since.

Its taxonomic story does not end there, however, as genetic tests soon revealed that a much more subtle and nuanced revision was worth considering. It was discovered that the forked spleenwort existed in two genetically distinct types, a diploid (having two sets of chromosomes) and a tetraploid (having four sets of chromosomes). Researchers found that each group had its own distinct distribution with the diploids centered in southwest Asia and the tetraploids being circumboreal.

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It was clear that a subspecies division was worth considering. Further investigations in the early 2000's revealed the presence of sterile triploid individuals that are believed to be hybrids of the two mentioned above. What's more, the forked spleenwort has been found to hybridize with other members of its genus. It is believed that the more isolated populations owe their existence in part to the isolation of their preferred substrate - these ferns do best on acidic substrates where competition is low - and decent longevity. It has been speculated that genetic differences can be maintained when "mutant" individuals become established and persist undisturbed for long periods of time.  

Regardless of its taxonomic status, the forked spleendwort is nonetheless a charismatic little species. A simple image search will reveal just how pleasant this species is in situ. Even better, its beauty and splendor can be shared by botanical enthusiasts throughout the northern hemisphere. There is something to be said about such species.

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

Further Reading: [1]

Closed on Account of Weather

Alpine and tundra zones are harsh habitats for any organism. Favorable conditions are fleeting and nasty weather can crop up in the blink of an eye. Whereas animals in these habitats can take cover, plants don't have that luxury. They are stuck in place and have to deal with whatever comes their way. Despite these challenges, myriad plant species have adapted to these conditions and thrive where other plants would perish. The intense selection pressures of these habitats have led to some fascinating evolutionary adaptations, especially when it comes to reproduction.

Take, for instance, the Arctic gentian (Gentianodes algida). This lovely plant can be found growing in alpine and tundra habitats in both North America and Asia. Like most plants of these habitats, the Arctic gentian has a low growth habit, forming a dense cluster of fleshy, narrow leaves that hug the ground. This protects the plant from blustering winds and extreme cold. From late July until early September, when the short growing season is nearly over, this wonderful plant comes into bloom. 

Clusters of white and blue speckled flowers are borne on short stems and, unlike other angiosperms that readily self-pollinate under harsh conditions, the Arctic gentian requires outcrossing to set seed. This can be troublesome. As you can imagine, pollinators can be in short supply in these habitats. What's more, with conditions changing on a dime, the flowers must be able to cope with whatever comes their way. The Arctic gentian is not helpless though. It has an interesting adaptation to these habitats and it involves movement.

Only a handful of plant species are known for their ability to move their various organs with relative rapidity. This gentian probably doesn't make that list very often. However, it probably should as its flowers are capable of responding to changes in weather by closing up shop. It is not alone in this behavior. Plenty of plant species will close their flowers on cold, dreary days. What is so special about the Arctic gentian is that it seems especially attuned to the weather. Within minutes of an incoming thunderstorm (a daily occurrence in the Rockies, for example) the Arctic gentian will close up its flowers. This is done via changes in turgor pressure within the cells. But what is the signal that cues this gentian in that a storm is fast approaching?

Researchers have investigated multiple stimuli in search of the answer. Plants don't seem to respond to changes in sunlight, wind, or humidity. Instead, temperature seemed to be the only signal capable of eliciting this response. When temperatures suddenly drop, the flowers will begin to close. Only when the temperature begins to rise will the flowers reopen. These movements are quite rapid too. Flowers will close completely within 6 - 10 minutes of a rapid decease in temperature. The reverse takes a bit longer, with most flowers needing 25 - 40 minutes to reopen.

So, why does the plant go through the trouble of closing up shop? It all has to do with sexual reproduction in these harsh conditions. Because this species doesn't self, pollen is at a premium. The plant simply can't afford the risk of rain washing it all away. The tightly closed flowers prevent that from happening. Also, wet flowers have been shown to discourage pollinators, even when favorable weather returns. Aside from interfering with pollen, rain also dilutes nectar, reducing its energy content and thus reducing the reward for any bee that would potentially visit the flower.

Being able to rapidly respond in changes in weather is important in these volatile habitats. Plants must be able to cope otherwise they risk extirpation. By closing up its flowers during inclement weather, the Arctic gentian is able to protect its vital reproductive resources.

Photo Credits: [1]

Further Reading: [1]

 

Meet Jones' Columbine

Meet Aquilegia jonesii. This interesting little columbine can be found growing in a narrow range along the northern Rockies. It only grows in alpine and sub-alpine zones, making it quite rare. It has a cushion-like growth form to shield it from the elements but disproportionately large flowers. It is a lucky day if one stumbles across this species! 

Fun Fact: Both the common name and generic name of the flowers referred to collectively as "columbines" have their origins in ornithology? 

That's right, the genus to which they belong, Aquilegia, can trace its origin to the word "aquila," which is Latin for "eagle." When the genus was being described, it was felt that the flower resembled the claw of an eagle. 

The word "columbine" has it's origins in the word "columba," which is Latin for "pigeon" or "dove." Early botanical enthusiasts felt that the nectar spurs resembled the heads of a group of doves. 

More and more I am coming on board with the idea that etymology can be quite fun.

Photo Credit: Steve (http://bit.ly/NbGbmz)

Further Reading: [1] [2] [3]

Of Pines and Crossbills

I would like to tell you a tale that involves three major players, the pine squirrel, crossbills, and lodgepole pines. The tale I am about to tell is an interesting one about speciation due to coevolution. Few examples in nature seem to play out so wonderfully apparent as this one.

Throughout most of the Rockies where lodgepole pines grow, the main seed predator is the pine squirrel. Crossbills are out-competed for this resource wherever the squirrels are present. Because of this, lodgepole pine cones have evolved methods to deter squirrel seed predation as much as possible. In Idaho, there are a few isolated mountain tops that have lodgepole pines but no pine squirrels. On these mountains, crossbills are the main seed predator and the pines have responded accordingly.

Crossbills are named because their bills are crisscrossed so that they can pry open the cone scales to get at the seeds. The trees in these isolated mountains have developed stouter cones with thicker scales that are harder to pry apart. The birds have responded by evolving shorter, deeper bills.

The most interesting thing about this response is the effect the new bill morphology has had on mating dynamics for the crossbills on these isolated mountains. Crossbills utilize calls to select mates. Also, crossbills prefer to flock with other crossbills that have similar calls. This is because beak morphology directly affects calls so by flocking with birds with the same call, crossbills can guarantee that the flock will find food sources that they can all utilize.

As beak morphology changes, so does the sound of the calls. It has been shown that the crossbills on these isolated mountains are showing preference for mating only with crossbills with the same bill morphology. Also, because they are the only crossbills that can utilize these lodgepole pines, they are one of the few crossbill populations that can stay in an area instead of migrating large distances to find other food sources.

These pre-mating isolation rituals are so strong on these mountains that the resident crossbills rarely mate with crossbills migrating through in search of food. In essence, the coevolution between these isolated lodgepole pine populations and the resident crossbills is driving these birds towards speciation. Whats more, this coevultion is estimated to have arisen only about 5,000 to 7,000 years ago.

On a side note, this may be a world record for how many times the word "crossbill" can find its way into a story.

Photo Credit: Perry van Munster and
nebirdsplus (http://bit.ly/1N42Ytf)

Further Reading:

http://www.jstor.org/stable/10.1086/511961

http://onlinelibrary.wiley.com/doi/10.1111/j.0014-3820.2001.tb01293.x/abstract