In the dioecious charophyte Chara canescens both sexually and parthenogenetically reproducing individuals occur in strict geographically separated regions: sexuals are restricted to only one population in Europe (Neusiedler See-Seewinkel, Austria), while the parthenogens occur across the whole of the continent. Ecology and distribution of sexuals in the Neusiedler See area have not been studied in detail yet. The relative abundance of male and female C. canescens varied between equal sex ratio and female-only populations. These results support a rather sympatrical than a strictly separated distribution of both reproduction modes in this area. Besides the varying sex ratio, a distinctive morphological feature for females of the different reproduction modes could not be identified. However, significant differences between ponds with different abundances of the sexes were observed in relation to the variability of some abiotic factors.