Cytotaxonomic observations on Villarsia (Menyanthaceae)

Abstract

Chromosome counts for five species of Villarsia indicate that x = 9 for the genus. In Australia one species is diploid, two species are hexaploid, and one species has tetraploid and hexaploid races. The South African V. capensis is tetraploid. Seed size differences in V. reniformis are not correlated with differences in ploidy level. One Australian species and V. capensis are distylous and strongly self-incompatible. Two homostylous species in Australia are self-compatible, but V. albiflora is homostylous and self-incompatible. Villarsia capensis is morphologically variable, but seems closely related to eastern Australian species. The amphi-Indian Ocean distribution pattern exhibited by this genus is an unusual one, and it seems doubtful if it can be accounted for by long-distance dispersal. The present range was perhaps achieved at a time when continental positions and climatic conditions were more favourable for overland migration than they are at present.