Dissertation Research: Systematics of Spigelia (Loganiaceae): Tropical/Temperate Relationships and the Origin of a Temperate Disjunction

点击翻译按钮获取中文摘要

9623495 Turner Graduate student Katherine Gould, with direction from advisers Billie Turner and Robert Jansen at University of Texas, is studying the American plant genus Spigelia of the Loganiaceae family, which has an estimated 50 species distributed in North, Central, and South America. Samples are being drawn from herbarium collections and from field expeditions in Mexico and elsewhere, to provide materials for both intensive morphological studies and for molecular analyses of nuclear DNA variation and chloroplast DNA restriction-enzyme variation. The goals are to assess morphological features that will provide reliable characters for distinguishing the species in the genus, and to infer a phylogeny of sections within the genus with the two molecular data sets, testing for concordance between them and integrating them in a combined-DNA database. One major test will focus on the three native species in the U.S. and assess whether these comprise a single evolutionary unit (a clade) or represent separate speciations into the north temperate zone. A subsidiary test will assess relationships between spigelias on opposite sides of the Mississippi River, in Texas and in Florida. %%% Modern taxonomic studies of plants combine morphological studies with newer molecular analyses. The morphological studies evaluate variation in vegetative and reproductive characters within and among populations in order to designate reliable features for identification and assess species status. Molecular (DNA) data allow measurement of mutational differences between species and the inference of phylogenetic (genealogical) relationships among them. With this phylogeny as guide, the geographical distributions of the species can be analyzed to detect migration pathways through time, and to determine whether single or multiple invasions have occurred. ***