Pollination Specialization and Protogyny in Myrrhidendron donnellsmithii (Umbelliferae)

Myrrhidendron donnellsmithii is a woody, andromonoecious member of the apioid Um- belliferae indigenous to Costa Rica. Hermaphrodite flowers are protogynous and concentrated in the outer umbellets of secondary umbels, while the primary and tertiary umbels consist almost entirely of male flowers. Neither hermaphrodite nor male flowers open fully, the petals remain erect with their tips strongly infolded, and together with the filaments form a floral tube, the base of which surrounds the nectariferous stylopodium. This tubular corolla probably excludes non- adapted flower visitors, but allows access to nectar by longer-tongued, specialized pollinators such as those seen visiting the umbels. As the staminal filaments form an integral part of the floral tube, protogyny is probably the most advantageous dichogamous system, because delay of male function postpones disruption of the tube following anther dehiscence.