Characterizing Quantitative Variation in the Glossopodia of Three Western North AmericanIsoëtesSpecies

One of the challenges when working with the genus Isoetes is the scarcity of in-depth comparative analyses of its morphological characters. This paucity of analyses relates in part to the long-held conclusion that most of the characteristics associated with the traits of the genus aside from spore morphology, are too variable to be informative. As a result, our understanding of morphological variability among species of Isoetes is underdeveloped. Recent workers have attempted to address this deficiency by examining the glossopodia of the ligule, a structure unique among living taxa to Isoetes and its sister genus, Selaginella. The glossopodium is embedded in the adaxial surface of the microphyll, and has shown evidence of interspecific variability in the few studies in which it has been examined. However, these prior works were limited to qualitative comparisons. The present study compares 3D reconstructions of the glossopodia of three species, Isoetes howellii, I. bolanderi and I. nuttallii, usi...