UC Riverside

Flowering plants have a remarkable diversity in sexual systems. These sexual sys- tems have ecological and evolutionary implications, yet comprehensive studies are hindered by the scarcity of species-level sexual system data. In this dissertation, we will focus on the genus Cylindropuntia (family Cactaceae), which although has a variety of sexual systems, has been poorly studied. My first goal is to accurately determine the sexual system of C. wolfii reported anecdotally as gynodioecious. To achieve this, we carried out experimental crosses and histological analysis of putative female and bisexual flowers. We found that C. wolfii is functionally dioecious where the putative bisexual flowers were actually function- ally male. Dioecious species often exhibit sexual dimorphism, which can have significant ecological effects, particularly in terms of plant-pollinator interactions. My second goal is to identify whether C. wolfii has sexual dimorphism and if that influences pollinator at- traction. We conducted a comprehensive analysis of quantitative and qualitative traits in C. wolfii flowers and compared them statistically. Our findings indicate that male flowers of C. wolfii are larger and more brightly colored, leading to a higher attraction of potential pollinators compared to female flowers. In this study, we utilized fluorescent dyes as pollen analogues, which are available in various colors. However, previous research has not investigated whether the color of these dyes influences pollinator attraction. Therefore, my third goal was to assess whether there is any bias in pollinator attraction due to the color of the dye. We conducted fluorescent dye assays on: Oscularia deltoides, which exhibits consistent flower coloration, and C. wolfii, which displays flower color polymorphism. We discovered that the presence of green dye influences the attraction of bees. Dioecy is hy- pothesized to lead to low genetic diversity and so my fourth goal was to determine whether the dioecious Cylindropuntia species have lower genetic diversity than hermaphrodites. We found that dioecious Cylindropuntia has comparable diversity to that of hermaphrodites. But, the overall genetic diversity of all Cylindropuntia were found to be low signaling the need for protection measures. Our study sheds light on sexual separation in plants and its influence on ecological and genetic factors.