Cyathodes divaricata (Epacridaceae)—the first record of a bird-pollinated dioecious plant in the Australian flora

Abstract

The geographically restricted Tasmanian endemic Cyathodes divaricata Hook.f. is functionally dioecious but, unusually, is pollinated by several species of nectarivorous birds including honeyeaters (Meliphagidae). It has evolved in a clade otherwise conforming to the typical dioecious pollination syndrome of small white flowers serviced by small insects. A number of its features are consistent with ornithophily in other Epacridaceae, including a tubular pendant odourless corolla, a winter peak in flowering and a copious diurnal nectar flow. However, the flower largely retains the white, insect-attractive colour of its congeners. Male plants have more and larger flowers, begin flowering earlier in the season, and yield significantly more nectar per flower than female plants. The fruits produced on female plants were 22% larger than the few produced on male plants. These findings are consistent with recent theories on the biology of dioecy. The species has a high level of self-fertility, and dioecy presumably serves to increase the rate of outcrossing.