Master of Science (MSc)
Faculty of Science
The genus Cuscuta (dodders, Convolvulaceae) is one of the most significant lineages of parasitic plants from economic, conservation, and anthropogenic perspectives. Members of the genus are twining stem parasites with no roots, lacking almost completely chlorophyll or its function, and gather required nutrition from their host via specialized haustorial connections. While there are almost 200 described species, problems with species identification exist because many diagnostic characters are restricted to their tiny flowers. Probably contributing to this identification difficulty is the fact that the group has not received taxonomic attention for over 75 years; even knowledge of its basic reproductive biology is sparse. Together these conditions have had negative consequences for applied research on this group. More recently, Cuscuta have witnessed a scientific rejuvenation. Molecular phylogenies have been published for 2 of the 3 major infrageneric lineages, 5 of the 15 clades of subg. Grammica have received taxonomic revisions, and work on their basic reproductive ecology has gained momentum. Still lacking, however, are reliable morphological characters that are able to support molecular phylogenies, aid in the description of new sections or species, or provide a solid morphological framework within which ecological variables can be compared. This work presents a thorough survey of the structural diversity of two of the most important, and systematically relevant, reproductive structures in Cuscuta: pollen and the gynoecium. While a number of characters were initially considered, a total of 15 qualitative and 14 quantitative characters were included in analysis. A reclassification of pollen and stigma morphology was required to better account for the variation that is present in these structures. Character states were coded using Thiele’s gap-weighting, and many of the characters were optimized onto a phylogenetic supertree that resulted from the combination of three large-scale phylogenies based on plastid trnL-F and nuclear ITS sequences. Key results are discussed in terms of their ecologic, systematic, taxonomic, cytological or developmental significance.
Welsh, Mark, "Evolution and Systematic Significance of Reproductive Structures in the Genus Cuscuta (dodders, Convolvulaceae): Pollen and Gynoecium" (2009). Theses and Dissertations (Comprehensive). 957.