Typically fringing or forming patches in the riverbed of rarely running rivers crossing arid zonal ecosystems in Namibia, Botswana and South Africa (Kuiseb R., Namib Desert and upper Swakop R. around Okahandja, Namibia); sometimes occurring on permanently running rivers crossing deserts (lower Kunene reaches, lower reaches of Gariep R. W of Augrabies Waterfalls); for the distribution map see Appendix S3