A comparative study of <i>Pleurosigma subrectum</i> and <i>P. acus</i> (Bacillariophyta)

Abstract

In continuation of an earlier paper on <i>Pleurosigma</i> species with an (almost) non-sigmoid valve and raphe sternum, a comparative study was made in LM and SEM of <i>Pleurosigma subrectum</i> and <i>P. acus.</i> For <i>P. subrectum</i>, slides and a subsample of the type material were examined. For <i>P. acus</i> no unmounted material permitting SEM investigation is extant; a sample containing specimens fully matching the type in LM was therefore used as epitype material for SEM. The original data on striation of <i>P. acus</i> are emended. No morphological differences indicating separate specific status of these two taxa were observed and <i>P. acus</i> is therefore here designated a heterotypic synonym of <i>P. subrectum</i>. From the data now available, this is a very widely distributed species. The study demonstrates the indispensable role of collections for investigations on the diversity and distribution of diatom species.