Cocconeis distans Gregory and Amphicocconeis debesi (Hustedt) De Stefano comb. nov (Bacillariophyta), an intricate taxonomical history

We present a taxonomical revision of Cocconeis distans and C. debesi based on historical collections from Hustedt, and live material sampled from leaves of Posidonia oceanica. Our observations clarify the specific morphology of the two taxa, which have been confused by past and modern authors. In addition, we demonstrate that the valve structure of C. debesi deviates from that of the genus Cocconeis, but agrees with that of the genus Amphicocconeis. Therefore, we propose a new nomenclatural combination, Amphicocconeis debesi. The study also provides additional information on the geographical distribution of these taxa. © 2006 by Walter de Gruyter