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When the sexual system of a rare plant species is complex, characterizing floral development, plant morphology, and subpopulation structure is essential for assessing reproductive potential. Availability of pollinator rewards and positioning of sexual morphs within inflorescences relates to outcrossing potential. We studied the complex sexual system of the recently discovered Euphorbia rosescens E.L. Bridges & Orzell, a rare species occurring in a single Florida county. Euphorbia rosescens has both monomorphic subpopulations of female plants and mixed subpopulations with male and andromonoecious plants. Most data on cyathia sex, inflorescence architecture, floral visitors, and fruit set came from one female subpopulation and one mixed subpopulation. Cyathia longevity, flowering phase, nectar secretion, pollen production, and viability were measured in female, male, and hermaphrodite cyathia. Female plants had fewer inflorescence levels and cyathia and significantly smaller cyathia than male and andromonoecious plants. Andromonoecious plants were larger and produced more cyathia relative to male plants. Within mixed populations, sex switching occurred in both directions between male and andromonoecious plants. Female plants did not switch sexes. Proximal to distal inflorescence levels transitioned from hermaphrodite to male cyathia on andromonoecious plants. Nectar secretion corresponded to initiation of staminate flowering, but in female cyathia stigmas were receptive approximately a day before nectar secretion. Pollen production and viability were similar in male and hermaphrodite cyathia. Fruit maturation was minimal, primarily observed on andromonoecious plants. Nectar availability, pollen rewards, trimorphic inequalities in inflorescence display, and low fruit set suggest high geitonogamy, thus limiting outcrossing potential for this species. [ABSTRACT FROM AUTHOR]

Simón-Porcar proposes an alternative origin in the evolutionary pathway to heterostyly as described in a model proposed by Lloyd and Webb. Below I summarize her key points and namely consider the implications of comparing her model to ideas within the Charlesworth and Charlesworth model. The hypothesis that she has chosen to propose is similar to ones that others have proposed for this same genus, thus I have tried to distinguish how Simón-Porcar's hypothesis differs from theirs, as well as give credit to their contributions to these ideas. Finally, I have added a few more suggestions related to testing her hypothesis. [ABSTRACT FROM AUTHOR]

In many gynodioecious species, gender differences have been documented. Previous studies on populations of Lobelia spicata consistently documented hermaphrodites having larger corollas than females, but inconsistencies as to whether females had higher fruit set or not. In this study we expanded the data set on floral morphology, and to relate morphological differences to potential reproductive output we recorded stigma pollen loads and pollen tube growth to the ovary for both genders from four populations. Also, individuals were bagged to determine if and how much self-pollen deposition occurred on stigmas. Because this species is self-compatible but protandrous, it was thought unlikely to be able to self-fertilize through autogamy. Hermaphroditic flowers were larger than female flowers in four out of the six flower traits analyzed. Overall, hermaphroditic flowers had larger corollas and stigma-nectary distance, but female flowers had longer and wider stigmas and more ovules. Open-pollinated hermaphroditic flowers received more pollen grains on the stigma than female flowers. Positive correlations were found between floral morphological traits and stigma pollen load, but only for hermaphrodites. Pollen was found on the stigmas of all hermaphroditic bagged individuals and on a few female bagged individuals, though pollen tube growth was quite limited. Lastly, population differences were found. This study has identified several floral morphological traits and pollen grain/tube differences between genders and among populations for Lobelia spicata, supporting overall patterns identified in other gynodioecious species and adding a more detailed description of differences between the reproductive biology of each gender for this particular species. [ABSTRACT FROM AUTHOR]