Taxonomic and biogeographical notes on Okavango desmids (Zygnematophyceae, Streptophyta) II: Genera Cosmarium, Xanthidium and Staurastrum

In the present paper, a sequel to an earlier discussion on desmid algae from the Botswana Okavango Delta and the annexed Namibian Caprivi Strip, 25 taxa belonging to the genera Cosmarium, Xanthidium and Staurastrum are dealt with. Nine taxa are newly described: Cosmarium doidgei var. depressum, C. fuelleborniforme, C. haynaldii var. africanum, C. moremiense, C. okavangicum, C. permaculatum var. bituberculatum, C. pseudotus, Xanthidium micracanthum var. angustatum and Staurastrum okavangicum. The names of four taxa are newly given or recombined: Cosmarium fritschii, C. haynaldii var. ambadiense, C. taxichondrum var. pentachondrum and C. thomassonii. The majority of the taxa discussed can be characterized as African endemics.