Ruta-Muraria

In my opinion at least, the smaller a plant is, the more character it has. Wall rue (Asplenium ruta-muraria) is a wonderful demonstration of this. The genus of ferns to which it belongs, "Asplenium," is rather large, containing somewhere along the lines of 700 species worldwide. 

Wall rue can be found growing both in North America and Europe. Its distribution is a reminder of the great land bridges that once connected the continents back when ocean levels were much lower than they are today. The specific epithet "ruta-muraria" roughly translates to "bitter herb of walls." Along with its common name, these seem to hint at where this tiny fern likes to grow. Indeed, at least in Europe, this is a fern of stone walls, growing among the myriad cracks and crevices where microclimates are favorable for its spores to germinate. 

In North America, however, wall rue seems to be a bit more picky. Wall rue is a calciphile meaning it can really only be found in abundance on natural limestone outcroppings. As a result, it is considered a threatened or endangered species throughout most of the continent. The aspect of its habitat I find most interesting is that the limestone it relies upon is the result of an ancient sea that covered parts of North America during the Silurian Period some 443.8–419.2 million years ago. Along with plenty other plants in these habitats, if it were not for the solidified remains of ancient marine organisms, these extant plant lineages would not be here, at least not in the way in which we know them. 

Another interesting aspect of wall rue biology is that this little fern is helping paleontologists in Europe discover potential glacial refugia - ice free areas where plants and animals were able to survive during the height of glaciation. Refugia were likely epicenters of biodiversity, which expanded to recolonize the continents once the ice sheets receded. 

Wall rue, as well as other rock ferns in the genus Asplenium occur in two forms in nature - a diploid form with two sets of chromosomes and a polyploid form containing multiple sets of chromosomes. Polyploids arise from mutated diploids and can be found growing over a wider range than their more restricted diploid parents. By studying the relatedness of different diploid populations, researchers are able to deduce where some glacial refugia may have been located. In this way, these tiny little ferns are offering a rare but clear window into the Earth's long gone past. 

Further Reading:
http://www.sciencedirect.com/science/article/pii/S0024406698902577

http://www.jstor.org/stable/41756114?seq=1#page_scan_tab_contents

http://plants.usda.gov/core/profile?symbol=asru2

American Heart's Tongue Fern

When looking for ferns, it is easy to have a specific kind of search imagine in your head. Your mind's eye is tuned into the long, lacy look of dissected fronds but there are ferns out there that will challenge you to break that mold. I have had the wonderful privilege of meeting some of these fern species this year, but there is one species in particular that has really stuck out.

Meet the American hart's tongue fern, Asplenium scolopendrium var. americanum. The hart's tongue, as you can see, is absolutely striking. Its long, slender, uncut fronds form a disheveled rosette and the sori running along the underside make each frond look like a big, green centipede. Asplenium scolopendrium itself is a wide ranging species of fern, growing on limestone outcroppings throughout Europe but populations in North America are rather sparse and disjunct. In fact, the U.S. Fish and Wildlife Service has listed it as a threatened species. There are some morphological distinctions between the European and North American populations but the major difference is in their number of chromosomes. European hart's tongues are diploid whereas North America's are tetraploid. Because of these differences, botanists consider them distinct varieties.

Why the American variety is so rare is not fully understood, but human activities have not helped matters. Mining, logging, and development have wiped out many historic populations of these ferns. Their habitat specificity mixed with their already low numbers make for little to no range expansion for most populations. They seem to grow in close association with dolomitic limestone, which is high in magnesium. 

They also seem to rely on a specific mix of bryophyte communities, low light levels, moisture, and snow pack in order to persist. Spores that land on significant bryophyte patches seem to germinate better. Young ferns seem to perform better in mixed light levels, especially near canopy gaps. It has also been shown that snow pack is directly correlated to the vigor of each population. In years with below average snow pack, the plants seem to have trouble retaining enough moisture to survive.

This is such an incredible species of fern. To lose it would mean a serious loss for our planet. There is a good effort being put forth to protect, study, grow, and form a deeper understanding with the American hart's tongue fern. The more we learn about this species, the better we can understand what it is going to take to ensure that it persists far into the future.

Photo Credit: James Johnson (http://imgur.com/a/J1Ez5)

Further Reading:
http://www.fws.gov/northeast/nyfo/es/amhtfrecovplan.pdf

http://www.bioone.org/doi/abs/10.3159/TORREY-D-11-00054.1

http://www.fs.fed.us/

http://www.centerforplantconservation.org/

Time

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There is something very special about old plants. They offer us a way of appreciating a timescale that we can never fully understand. I am especially fond of finding people who have had house plants in their family for generations. I grew up with a few that had already been around for decades before I was born. Here is a wonderful example of what I am talking about. This Acronia titan orchid has been blooming for years and has acquired a wonderful little moss patch in the crux of its leaf. Out of that moss grows a fern.

This photo comes to us courtesy of Kevin Holcomb. You can find him on instagram via @orchid_beard