Sex-Ratios in a Gynodioecious Plant Ptilotus obovatus (Gaudich) F-Muell (Amaranthaceae)

Abstract

Ptilotus obovatus is a gynodioecious perennial shrub with diploid and tetraploid cytotypes and is widespread in arid Australia. This study involved sex ratio counts in colonies of both cytotypes across much of the species range. Samples from diploid colonies had high frequencies of females (>55%) in Western Australia, low frequencies (<41%) in South Australia, and variable frequencies (36-77%) in southwestern Queensland. Tetraploid colonies had the opposite trend with low frequencies of females (<47%) in Western Australia and high frequencies (>54%) in the Northern Territory, South Australia and New South Wales. Ptilotus obovatus appears to be subdivided into at least five biotypes with distinct ploidy levels and sex ratios. We suggest that tetraploidy arose at least twice from diploid ancestors with different sex ratios and that the present distribution of cytotypes may reflect dispersal from refugia after recent arid maxima.

The study of the genetics of male sterility in this species was impeded by the remarkably low seed set of plants in glasshouse crosses and in the field.