Sunday, February 7, 2010

Rafinesque and the Resurrection of Polygonum bicorne

Constantine Samuel Rafinesque was a strange man. I can’t stress that enough. When you look him up on Wikipedia you quickly realize that he was different. His name is preceded with such erudite appellations as polymath, autodidact and polyglot, besides the more familiar terms of botanist and zoologist. But this post isn’t about Rafinesque, or at least not directly so. Indirectly, it has to do with his eyes and what they saw. You see, where others missed the trees for the forest, Rafinesque perceived entities hidden deep within morphologies. Ever the avid publisher, he described many of these entites as taxa (usually species) new to science. Since his death, the oscillations of botanical treatments and nomenclatural innovations have alternately celebrated his insights and condemned his indiscretions. Few authors have had as many taxa bounced in and out of synonymy for so many decades. Polygonum bicorne, the focus of this post, is a fine example of this.
Rafinesque described Polygonum bicorne in 1817. It is morphologically similar to the more common and widespread Polygonum pensylvanicum which was described by Linnaeus in Species Plantarum in 1753. Both have eciliate to short-ciliate ocreae summits and both have stipitate glandular pubescence on the peduncles. They differ in that the flowers of P. bicorne are heterostylous (different types of flowers on plants) where those of P. pensylvanicum are homostylous (all the flowers morphologically the same). The flowers of P. bicorne differ from one another (heterostyly) in that some flowers have exerted styles and others have exerted stamens. To be clear, all the flowers of P. pensylvanicum lack exerted stamens and styles. Also, the achenes of P. bicorne, which are two-sided, have a distinct bump in the middle of one side, while those of P. pensylvanicum are smooth on both sides.
Field characters for the two are subtle and their use requires experience with each. Polygonum bicorne tends to branch profusely from the base and grows with a squat, globose silhouette. It has smaller, narrower leaves and very open flowers. Polygonum pensylvanicum grows more as single stems or small clumps but usually in a more upright condition. It has larger, wider leaves and nearly closed flowers. Furthermore, the flowers of P. bicorne are usually deep pink, while those of P. pensylvanicum range from off-white to pink. The habitat of each includes disturbed wetland communities but the range of P. bicorne is nearly limited to the central Great Plains. Polygonum pensylvanicum ranges throughout eastern North America east of the Rocky Mountains.

In the field these two species are distinct but when P. bicorne is peeled from the plant press its flowers can appear closed or partially closed and thus it becomes artificially similar to P. pensylvanicum. Enter Professor Twist (Google him for a quick chuckle). Full of well intentions and hungry for something interesting to share with the world, he starts pulling specimens from the stacks which are often mixed with misidentifications in both directions. Not seeing the distinctions that are so striking in the field, he pronounces that these two entities are better treated as one widely varying organism. Almost without exception, there is no one to rebut; or at least no one with a voice. And so a species is lost to ignorance through an ill concept of science; at least until the resurrection.

This brings to light a general problem. No field of science witnesses as much conceptual ebb and flow as taxonomy. It is also about the only field of science where opinion, rather than evidence, reigns supreme. Morphometrics, a powerful tool at the species level, is rarely used. Instead, taxonomic “treatments” are often based on what an author “thinks” are taxa without reference to how it directly relates to the organisms in question or the previous author’s concepts. Repeatability, the hallmark of good science, is thrown out the window. This wishy-washy, literature-based flip-floppery has served to usher in the molecular era; under the guise of resolution. Sadly, molecular taxonomy only offers a trade of one type of uncertainty for another. But because that uncertainty comes with the numerical averages of averaged averages, it is somehow construed as quantitative. Field folks (I reserve the title of botanists) that have the daunting task of applying this taxonomic maelstrom to management decisions are left confused, agitated and ultimately apathetic. Shamefully, they are forced to follow whatever is “up to date” (i.e., in fashion) or the renderings of their local floristic text, if they are lucky enough to have one.

Because Rafinesque spent so much time in the field, and because he knew the flora so well, he was able to decipher and describe many cryptic species. Field-based botany was more the rule than the exception for the first two centuries of American scientific exploration. Many contemporary scholars, lacking the field miles of their predecessors, now busy themselves with shotgun revisions. In their wake, taxa such as Dichanthelium, Aster and Andropogon (at least in terms of Little Bluestem) are pushed and pulled into bizarre contortions. So when a creature as valid as Polygonum bicorne, though now in the genus Persicaria, resurfaces as a good species, rays of hope beam throughout the forests, woodlands and prairies. The content hearts of lowly field botanists, seeking a touch of Rafinesque’s vision, being the ultimate source.