CRATICULA ELKAB (O. MULLER EX O. MULLER) LANGE-BERTALOT, KUSBER & COCQUYT, COMB. NOV. - TYPIFICATION AND OBSERVATIONS BASED ON AFRICAN SEDIMENT CORE MATERIAL

摘要

Otto Muller's published data and pictures of Navicula elkab were re-evaluated and comparedwith literature data and a Holocene sediment core material from Ounianga (Chad, Africa).A valid name under Craticula is provided and a lectotype and an epitype are selected. Anunusual siliceous covering over the valves is discussed.The taxon Navicula elkab O. Muller was first described in 1899 from El Kab (formerlyUpper Egypt, now Sudan) and has been the subject of discussion for about 30 years. Metcalfe(1990), Compere (1975), Archibald (1983), Schoeman & Archibald (1988) and Gasse (1975,1986) published data, based on a wider species concept than Muller, particularly with respectto valve size and the number of striae in 10 mu m. The taxon is of great importance inenvironmental research, because it is considered a good indicator of strongly alkaline watersin East Africa (Hecky & Kilham 1973, Gasse 1986). It was also reported as a dominantspecies in Holocene cores from Africa (unpubl. data) and Mexico (Metcalfe 1990, 1994).