Barrington, David , Cook, Kelsey .
An inquiry into the boundaries between species and their hybrid: the case of Polypodium x incognitum.
We examined the leaf morphology and stomate size of two New England fern species and their hybrid in the genus Polypodium (Polypodiaceae). While some morphological differences between tetraploid P. virginianum, diploid P. appalachianum, and their triploid backcross hybrid P. X incognitum, such as frond size, leaf tip shape, and spore size, have been previously described, the three are often difficult to distinguish. This is especially true in the field. Because no clear morphological boundaries exist between these taxa, we searched for understudied characters in leaf morphology that could aid in identification. Intact leaves were collected from plants from three habitats differing in geochemistry and elevation in Chittenden County, Vermont. A series of points were placed at even intervals along the margin of each leaf. This was also done within a single leaflet. Length and width of stomata were measured to yield an approximate mean stomate area. These measurements were used to inferploidy level, as plants with more sets of chromosomes tend to have larger stomata. Plants with irregular spores were designated as sterile triploid hybrids. The putative hybrids fell in the middle of the stomate size range. A Principal Components Analysis based on the coordinates of the points on the leaf margins was used to reveal the morphological characters that best accounted for the variability between the plants. Regressions were also done between different Principal Components and stomate size. No single leaf characteristic was found that could conclusively differentiate the species and hybrid. There was substantial overlap between the two species. For both the pinnae and whole leaves, hybrids were often intermediate but could be more similar to one progenitor than the other. Occasionally they were more extreme than either. This could either indicate a failure of this method to capture differences between the taxa or that there is extensive overlap between them.
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1 - University Of Vermont, Jeffords Hall, 63 Carrigan Drive, Burlington, VT, 05405, USA
2 - University of Vermont, Plant Biology, 111 Jeffords Hall, 63 Carrigan Drive, Burlington, VT, 05405, USA
Presentation Type: Poster:Posters for Sections
Location: Battelle South/Convention Center
Date: Monday, July 9th, 2012
Time: 5:30 PM