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Groundwater Thresholds For Root Decomposition And The Relation To Barrier Island Ecological State Changes, Matthew Lee Smith

Biological Sciences Theses & Dissertations

Barrier islands off the eastern shore of Virginia exhibit distinct habitats that abruptly transition between periodically brackish/freshwater marshes, wooded swales, and sparsely vegetated dunes. There is strong evidence that the plant communities and ecosystem processes occurring in each habitat are primarily influenced by nutrient availability and the distance between two of the three free surfaces: land and freshwater. At the Virginia Coast Reserve-Long Term Ecological Research Site in Virginia, USA, thresholds to belowground decomposition rates were identified by measuring decay of native roots and rhizomes at 32 elevations in relation to mean annual groundwater levels (-0.356 – 1.937 m). Negative …

Molecular Phylogeny Of The Genus Houstonia And Allies In Rubiaceae, Hunter Lee Shanks

Biological Sciences Theses & Dissertations

Houstonia (Rubiaceae) is a strictly North American genus of 24 species distributed from Mexico, throughout the United States, up to Canada. Houstonia has proven to be a taxonomically difficult genus since the Linnaean description of Houstonia and the related genera: Hedyotis and Oldenlandia in 1753. For over 250 years botanists have lumped and separated Houstonia from Hedyotis and Oldenlandia based on various morphological characters. The most recent circumscription of Houstonia (Terrell 1996) separated the genus into two subgenera with each subgenus containing two sections. Nuclear (ITS) and plastid (trnL-F, rps16) DNA sequences were used to build a molecular phylogeny depicting …

Molecular Phylogenetics And Historical Biogeography Of The Tribe Chiococceae (Rubiaceae), Sushil Kumar Paudyal

Biological Sciences Theses & Dissertations

Chiococceae are a monophyletic assemblage of morphologically very diverse groups of plants ranging in habit from subshrubs to shrubs to tall trees exhibiting an astonishing variation in shapes and sizes of corolla, and kinds of fruits and seeds. They are primarily distributed in the Neotropics but also occur in the West Pacific islands; thus exhibiting amphi-Pacific tropical disjunction. This study addresses the phylogenetic relationships and biogeography of the Chiococceae using molecular DNA sequence data, and presents novel data on the tribal and generic delimitations, intergeneric relationships, and the origin and dispersal of this group.

In the most recent tribal delimitations …