Date of Award
Honors College Thesis
Mac H. Alford, Ph.D.
A large and unusual population of Isoetes (Isoetaceae, Lycopodiophyta) in the DeSoto National Forest, Wayne County, Mississippi, was studied to determine if the individuals there represent a new species or if they represent part of the variation of the one primary species of the longleaf pine belt of Mississippi, Isoetes louisianensis, which it most closely resembles. The unusual population and specimens of known Isoetes louisianensis were examined comparatively based on morphology, megaspore ornamentation, examination of habitat characteristics, and phylogenetic analysis of DNA sequence data from the nuclear internal transcribed spacer 1 and 2 (ITS) and the 5.8S ribosomal gene. No differences were discovered between the populations in DNA sequence data, small differences were discovered in megaspore ornamentation and habitat, and more significant differences were discovered in morphology, although all of the differences were based on small sample size. Thus, the results of this study are inconclusive as to the species status of the unusual Isoetes population. However, the detailed environmental data collected in the drainage do show that senescence (loss of leaves) closely follows water levels, not temperatures or seasons, as some have hypothesized. This study augments scientific understanding of Isoetes louisianensis, considering that much about this species is still unknown due to many new, recent discoveries of populations, similarities in appearance with other species of Isoetes, natural occurrences in Isoetes of cross-fertilization with the production of sterile hybrids, variations in ploidy level, and the need for scanning electron microscopy to carefully observe megaspore ornamentation. Plans have been made to continue assessing the v unusual Isoetes population and typical Isoetes louisianensis populations based on chromosome numbers, vegetative anatomy, and phylogenetic analysis of additional DNA regions.
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Walker, Shannon L., "Morphological, Genetic, and Environmental Characterization of an Unusual Population of Isoetes (Isoetaceae, Lycopodiophyta)" (2017). Honors Theses. 539.