Navicula nielsfogedii JC TAYLOR & COCQUYT sp nov., a new diatom (Bacillariophyta) from tropical and sub-tropical Africa

In this paper we describe Navicula nielsfogedii sp. nov., a commonly occurring diatom through central and southern Africa and distributed from the sub-tropical zones of South Africa to tropical central Africa. We have examined the material of the most closely related species described from Africa, Navicula feuerbornii f. africana Foged and suggest that this species may be conspecific with Navicula heimansioides Lange-Bertalot and to have no link to the taxon N. feuerbornii Hustedt sensu Simonsen. With reference to Navicula feuerbornii f. africana we also discuss the changes over time in diatom species concepts, what we have dubbed ` species concept drift', and the consequences this holds for accurately identifying diatom taxa. As the newly described species is widely distributed and common in some samples from tropical and subtropical Africa we conclude that it may be a useful additional indicator organism for water quality monitoring in the region.