XVI International Botanical Congess

The marine angiosperms are perhaps one of the most highly adapted groups of flowering plants. Sexual reproduction in the ocean is problematic due to the difficulty in getting pollen to stigma in a 'wet' medium i.e. hydrophily. It appears that the remarkable seagrass pollen which is either long and filamentous (up to 500 µM long) or embedded in thick mucous forming long strands, have been selected to allow successful pollination. Previous workers have hypothesized that these adaptations and the remarkable frequency of dioecy among the seagrasses (>75% of species) is evidence of selection for outcrossing among a group with hydrophilous pollination. In my presentation I will discuss this model in light of a growing body of data suggesting that the 'outcrossing model' does not explain what we know about seagrass breeding systems and that breeding system evolution among seagrasses depends upon phylogenetic relationships and an interaction with their environment.