Floral development of dioecious staghorn sumac, Rhus hirta (Anacardiaceae)

The organogenesis of floral development in the dioecious clonal tree species Rhus hirta (Anacardiaceae) offers an excellent model system to study gender expression in dioecious plants. Pistillate and staminate flowers from developing inflorescences were collected from Grover Island, located off the northern shore of Prince Edward Island, Canada. The developmental morphology of both floral types was studied using scanning electron microscopy. The early stages of floral development of R. hirta are essentially the same in the two sexes. Both the stamen and carpel primordia are initiated in male and female flowers. Furthermore, the primordial sex organs on both flower types show striking similarities in size and symmetry as well as sequence of initiation in the early stages of development. During the later stages of development, the stamens in the female flowers and the gynoecium in the male flowers abort, resulting in very different morphologies at maturity. Statistical analyses revealed that the height of the mature gynoecium and stamens as well as the length of the petals differed significantly between sexes. This species may be reflecting its relationship to hermaphroditic ancestors during the early stages of development.