The Vittadinia group is comprised of 11 genera in the Astereae tribe. Most members of the Vittadinia group occur on the continent of Australia and several of the larger genera extend their distribution across the Pacific to Hawaii and the Cook Islands. Recent studies of the phylogenetic relationships of the genera have revealed marked homoplasy in molecular data and in morphological features, particularly those associated with the breeding system. Past inter-generic hybridization events could explain, in part, the considerable degree of homoplasy observed. Here we report results of greenhouse studies on variation in sex expression, self-incompatibility and infrageneric/intergeneric cross-compatibility, in five of the largest genera: Vittadinia, Tetramolopium, Minuria, Camptacra, and Peripleura. Minuria, Camptacra, and one section of Tetramolopium are monoecious while Vittadinia, Peripleura, and the remaining two sections of Tetramolopium are gynomonoecious. Self-incompatibility is strongly correlated with monoecy. Phylogenetic analysis indicates that monoecy has been gained and lost more than once, and hence so has self-incompatibility. Crossing studies readily obtained interspecific hybrids in all five genera with high pollen fertility in most cases. Intergeneric hybrids resulted among a majority of the attempted combinations. Intergeneric hybrids were obtained between Hawaiian and Australian taxa and possessed surprisingly high pollen fertilities. Therefore, ancient intergeneric hybridization may well have had a role in generating diversity in this group.

Key words: Asteraceae, hybridization, monoecy, self-incompatibility, Tetramolopium, Vittadinia