XVI International Botanical Congess

Introgressive hybridization has been important in the evolutionary history of many plant groups. These factors may be especially important in island populations. Patterns of gene flow were examined in three hybrid swarms of Penstemon davidsonii X P. rupicola (Scrophulariaceae) using a combination of morphological characters and ISSR data. Hybrid plants were subdivided into morphological groups and the proportion of species-specific bands in each morphotype were calculated. Hybrid swarms show intermediate proportions of species-specific bands to the parental species. The proportion of species specific bands in hybrid plants suggests a pattern of unidirectional gene flow from P. rupicola into P. davidsonii. Current investigations are focusing on elucidating mechanisms of the observed gene flow patterns.