Two in the bush: On the evolution, distribution and natural history of dioecy in Australian Solanum

Date of Completion

January 2006


Biology, Botany




The causes, consequences, and correlates of dioecy have been the subject of much discussion since the days of Charles Darwin's work. Several more recent authors have stressed the importance of informing this body of theory with studies that focus on lineages in which both dioecy and hermaphroditism are present. The genus Solanum is an ideal group for this kind of analysis because dioecy, hermaphroditism, and potential unisexual transitions between them all occur. I present phylogenetic hypotheses for the Australian species included by Symon in Solanum subgenus Leptostemonum (the "spiny solanums") section Melongena. Ten of the 14 currently described dioecious species in the genus are included in this group. Phylogenetic results from ITS, trnK-matK , and morphological datasets support a single origin of dioecy in Australian Solanum. I hypothesize that that was followed by a radiation of perhaps 12 new species in the subarid tropics of northern Australia. The transition to dioecy in Australian Solanum originated from a widespread background of andromonoecy in subgenus Leptostemonum. The causes, mechanisms, and maintenance of dioecy in Australian Solanum are explored within a natural history context. Specifically, the roles of local pollinator and frugivore communities are discussed. This study significantly improves the understanding of a poorly known group of species within an economically-important plant group, and should contribute in a positive way to conservation efforts focusing on rare and unusual spiny solanums and their habitats in northern Australia. ^