Studies on Amphora subgenus Halamphora (Bacillariophyta): the revision of some species described by Hustedt using type material

As part of an analysis of type material of Amphora species described by Hustedt, the lectotypes of Amphora fontinalis, A. rugosa and A. schroederi and the holotype of A. subturgida were analysed. Light microscopy showed that all these tropical freshwater taxa are similar in frustule and valve outline, position of the raphe, appearance of the dorsal striae and thickening of the central dorsal virgae. Scanning electron microscopy allowed reliable differentiation between the four, based on the morphology of dorsal striae, dorsal areolae, conopeum, proximal raphe fissures, presence or absence of an inner longitudinal rib close to the raphe sternum, and degree of thickening of the central dorsal virgae. Previous reports of A. fontinalis from Tahiti and Moorea were confirmed while reports of this species from Australia and of A. subturgida from Mauritius, Papua and Israel were refuted. Based on our results, species descriptions are emended and the distributions of these four species are revised. Comparisons of these species and others of the subgenus Halamphora are presented.