Master of Science (MSc)
Faculty of Science
Cuscuta (dodder) includes ca. 200 species of plant obligate stem parasites with both ecological and economical significance. Inflorescences have been historically used in Cuscuta for species descriptions and identification keys, but no comprehensive study exists to date. The main objective of this study was to survey the diversity of inflorescences, and to understand their evolution and possible form-function relationships. The inflorescence architecture of 132 Cuscuta taxa was analyzed using herbarium specimens, and eight species were grown to study their inflorescence development. Inflorescence traits were mapped into a genus phylogeny obtained from a combined analysis of nuclear ITS and plastid trnL-F sequences. To test the hypothesis that inflorescence architecture is connected to sexual reproduction, correlations between inflorescence traits (using Principal Components), and sexual reproductive traits (pollen to ovule ratios, fruit diameter, and modes of dehiscence) were analyzed. Based on their development, three major types of inflorescences were observed: “Cuscuta type”, a simple, monochasial scorpioid cyme; “Monogynella type”, a compound monochasial scorpioid cymes, with the longest primary axes having prolonged vegetative growth giving the appearance of thyrses; and “Grammica type”, a compound monochasial scorpioid cymes with up to 4 orders of axes. Parsimony and maximum likelihood analyzes inferred Monogynella as the ancestral type, while Cuscuta and Grammica were derived. Overall, the total length of axes exhibited a reduction trend throughout the genus evolution. Positive significant correlations were noted between the general size of the taxon and pollen-ovule ratios, and the general size of the taxon and fruit width. This suggests that the same breeding system may have different inflorescence architectures. Several modes of dehiscence had significantly different total axes lengths, suggesting that infructescence architecture is connected to the modes of dehiscence in Cuscuta and therefore seed dispersal.
Glofcheskie, Morgan, "Diversity and Evolution of Inflorescences in Cuscuta" (2022). Theses and Dissertations (Comprehensive). 2502.