Analysis of some species resembling Fragilaria capucina (Fragilariaceae, Bacillariophyta)

Based on literature data, Fragilaria capucina seems to be a widespread species, often split into a large number of varieties. In the present study, the original type material was investigated, together with the type material of two varieties, originally described by Grunow as the var. acuta and the var. acuminata and the type material of Fragilaria sandellii and F. nevadensis. The results of all morphological analyses indicated that F. capucina is clearly different from the other species based on the number of rimoportulae, valve outline and spine morphology. The var. acuta and var. acuminata are conspecific with F. nevadensis and are added as synonyms of the latter. Additionally, three unidentified populations from Sweden and the United Kingdom that showed some resemblance to F. capucina were analysed. Using detailed LM and SEM observations, these three populations showed sufficient morphological differences from all other Fragilaria species and are therefore described as new for science: F. malouana Van de Vijver et Jarlman nov. sp., F. battarbeeana Van de Vijver, M.Kelly, C.E.Wetzel et Ector nov. sp. and F. ennerdalensis Van de Vijver, M.Kelly, C.E.Wetzel et Ector nov. sp.