Sectional revision, speciation, and population biology in Lycopodium (Lycopodiaceae)

The family Lycopodiaceae is well represented in a fossil record that extends 400 Mya to Carboniferous swamps. Extant lycopod species, however, bear little resemblance to this rich and diverse history. The globally distributed genus Lycopodium contains about 60 described species that are partitioned into nine infrageneric sections. Past studies have revealed obscure relationships among sections. With their small sample sizes (≤14 species), published studies of cpDNA sequences supported sectional boundaries within Lycopodium with varying bootstrap support, but disagreed on the relationship among sections. This dissertation integrates new DNA sequence data from the chloroplast (rpl16 intron) and mitochondrial (mt small subunit gene) genomes with sequences from earlier studies to propose new hypotheses concerning sectional relationships in Lycopodium. Congruence among data and methods of analyses provided new perspectives on intersectional relationships in Lycopodium. Data analysis demonstrated a major split early in the Lycopodium lineage that united Southern Hemisphere sections as a monophyletic group. An exception was the sister relationship between Sections Diphasium and Obscura, the latter section having members restricted to northern portions of the globe. Morphological and chromosomal data were analyzed in light of the topologies generated using molecular data. Similarities in sporophyll development and lack of a mucilage canal, as well as spore type, were traits that corroborated clades suggested from sequence data.;Increased taxon sampling and the rpl16 intron sequence data revealed very low levels of sequence divergence among species within Lycopodium sections. Alternative methods were implemented to explore questions of species boundaries in Section Obscura. Banding patterns produced from protein electrophoresis failed to show variability, but techniques targeting genome-wide fragment polymorphisms were more successful. In particular, AFLP technology uncovered significant genetic differentiation among four species in Section Obscura. Both similarity and cladistic analyses clustered species groups, but phenograms produced using a distance method (UPGMA) recovered bounded species clusters best; neighbor-joining and parsimony methods were less successful. Phenograms revealed L. obscurum and L.dendroideum as discrete groups, but L. hickeyi was ancestral to both L. obscurum and L. juniperoideum.;To consider the influence of environmental pressure on the ecology and morphology of species, two years of pre-treatment and five seasons of field data following treatment were accumulated on populations of Lycopodium dendroideum. Analyses of these plots revealed the effect of over-story canopy, with or without horizontal stem damage, on aerial stem production and vegetative community structure. There was a significant decrease in stem production between treated and control plots, but no difference in L. dendroideum stem productivity was found between plots receiving only a reduction in surrounding canopy or those with over-story removal and stem damage. The decrease in vertical shoots was not significantly correlated with ensuing drought conditions. In contrast, strobili production, overall species richness, and most vegetative class measures were negatively correlated to precipitation. A reduction in surrounding canopy, and the suspected photooxidative damage experienced by aerial stems, had the greatest impact on L. dendroideum survival and persistence.;The results from systematics and speciation studies were integrated to revise hypotheses about the evolutionary history of Lycopodium and Section Obscura. Field studies were examined in light of these hypotheses, and questions on survival and growth in club moss populations addressed. These studies provide new data for understanding ancient lineages and explaining their persistence while facing present-day selective pressures.