Revision of the Psammothidium manguinii complex (Bacillariophyta) in the sub-Antarctic Region with the description of four new taxa

Psammothidium manguinii is a common constituent of the limnoterrestrial diatom flora of the Antarctic Region. The species shows a broad variability in several morphological and morphometrical features such as valve outline, valve width, striation pattern and length/width ratio. Analysis of the type material of Achnanthes manguinii, described by Hustedt in 1952, and A. manguinii var. elliptica, described by Manguin two years later, together with an analysis of a large number of P. manguinii populations from the sub-Antarctic Region (with samples from all major islands in the southern Atlantic, Indian and Pacific Ocean), resulted in a clear morphological revision of the species. Four new species are described, P. acutomanguinii sp. nov., P. antarcticum sp. nov., P. mannensianum sp. nov. and P. hodgsonii Van de Vijver et Verleyen sp. nov., whereas the former variety elliptica is brought to species level: P. ellipticomanguinii nom. et stat. nov. The morphology, ecology and distribution of all species are discussed and a morphological comparison is made.