Phylogeographic Analysis of Rare Lady\u27s Tresses Orchids (Spiranthes) from Missouri and Indiana

Spiranthes is a terrestrial orchid distributed mainly throughout North America, and many species in the genus have some form of conservation listing in at least one of the United States of America. I used Amplified Fragment Length Polymorphism (AFLP) markers to determine the phylogenetic relationships of seven Spiranthes species from Missouri and Indiana, and the possible origin of disjunct Indiana populations. S. magnicamporum shares many morphological traits with S. cernua, and is difficult to discern from it. Here I tried to find the molecular basis to differentiate them. Twenty-nine samples from seven Spiranthes species from two states produced a total of 181 polymorphic markers with two selective primer combinations for AFLP reactions. Phylogenetic analysis of the entire data set implies that S. magnicamporum is derived from S. cernua. Analysis of only S. magnicamporum and S. cernua gave four clades, including one group of S. magnicamporum. The other clades include both species, suggesting the possible origin of S. magnicamporum from S. cernua. Phylogenies indicate that there is not a good phylogenetic basis for splitting S. cernua and S. magnicamporum into two species. This is supported by lack of good morphological characters to distinguish them and the position of S. magnicamporum, which is nested within S. cernua in a parsimony tree, and thus is likely to be the same species. The average genetic distances based on AFLPs within and among groups of S. magnicamporum and S. cernua are nearly equal regardless of the species or location, suggesting that gene flow may be the same within and among both populations and species. This may indicate a lack of genetic divergence across geographic distances and species and that disjunct Indiana populations are either recent remnant or recent colonizations, but not ancient remnants