Hermaphroditism and dichogamy in Stilbocarpa polaris (Araliaceae) on Campbell Island

Abstract

Since its scientific discovery in 1844, the breeding system of Stilbocarpa polaris (Araliaceae) has been described as polygamo-dioecious with either unisexual or hermaphroditic and female flowers. A short study of flower sex expression, on subantarctic Campbell Island, found evidence that all flowers are cosexual, protandrous and strictly dichogamous, such that whole inflorescences are either presenting pollen or stigmas. Circumstantial evidence also suggests that S. polaris is self-compatible but self-fertilisation would be largely avoided by this synchronous dichogamy. Pollination is most likely effected by small diptera which congregate on inflorescences.

Keywords:

• breeding system
• dioecy
• hermaphroditism
• megaherb
• subantarctic

Acknowledgements

We thank the Department of Conservation for permission to work on Campbell Island; Henk Haazen, captain of Tiama and the captain and crew of HMNZS Otago for transport; Lynne Huggins, Lorna Little and Vickey Tomlinson for assistance in the field; Colin Webb for helpful comments on an earlier draft.