Analysis of the type of <i>Achnanthes exigu</i> Grunow (Bacillariophyta) with the description of a new Antarctic diatom species

A study was made of the type material of Achnanthidium exiguum (Grunow) Czarnecki. This often encountered and apparently ubiquitous species was originally described as Stauroneis exilis by Kützing from the island of Trinidad and later re–named as Achnanthes exigua by Grunow. The type material for this taxon (Kützing sample 397), housed in the Van Heurck collection at the National Botanic Garden of Belgium, Meise was investigated and the ultrastructure of this taxon was documented using both LM and SEM observations. A new Antarctic taxon, formerly identified as A. exigua, was described as a new species, Achnanthidium australexiguum sp. nov. The position of both taxa within the genus Achnanthidium is briefly discussed