Master of Science (MSc)
Faculty of Science
Dr. Mihai Costea
Cuscuta is a genus of nearly 200 obligate stem parasites with a nearly cosmopolitan distribution and considerable agricultural and ecological significance. Dodder seeds are considered “unspecialized”, with no morphological adaptations towards particular dispersal vectors; however, the seed coat anatomy has recently suggested an adaptation to endozoochory. This is the first attempt to provide a genus-wide overview of the diversity in morphology and anatomy of Cuscuta seeds, together with an assessment of the water gap and exploration of various form-function relationships. I surveyed 104 species belonging to all four Cuscuta subgenera. Seeds of the species of the first infrageneric dodder lineage diverged, subg. Monogynella, exhibit epidermal cells that are elongated and puzzle-like, morphologically uninfluenced by dryness/wetness (Type I) and possess a seed coat with an incomplete outer palisade layer. In contrast, epidermal cells of the other subgenera, Cuscuta, Pachystigma and Grammica, are more or less isodiametric and have evolved the ability to alternate their morphology and physiology between two states: deeply pitted when dry, and papillose through hydration (Type II). With the exception of four species, taxa of these three subgenera have a complete outer palisade layer throughout the entire seed. An embryo with a globose radicular end has evolved in sect. Denticulatae and sect. Subulatae of subg. Grammica, likely in connection with a storage function. In this thesis, I also examined the route of water entry — the water gap, in seven species and suggested two possible mechanisms for initial physical dormancy break. I investigated the relationship between seed size and geographical distribution as well as between the average number of seeds per capsule and the breeding systems. Finally, using other characters, such as the seed size, hilar region morphology, seed coat micromorphology and the number of palisade layers, I prepared an identification key for 16 species present and of concern in Canada.
Olszewski, Magdalena, "Diversity and Evolution of Seeds in Cuscuta (dodders, Convolvulaceae): Morphology and structure" (2019). Theses and Dissertations (Comprehensive). 2186.