Abstract
Psammothidium germainii is a widespread freshwater monoraphid diatom species in the Antarctic Region. Detailed analysis of the populations in the different parts of the Antarctic Region revealed the presence of several species that were lumped under the name 'P. germainii'.
The type material of both Achnanthes germainii and Achnanthes ninckei has been investigated to allow a better morphological delimitation of both taxa and to better characterize the new taxa. Two new taxa are proposed: Psammothidium rostrogermainii sp. nov., typical for its rostrate apices and its rather distantly spaced stria pattern, and Psammothidium germainioides sp. nov., formerly identified in Antarctica as Achnanthes ninckei.
Both new taxa are illustrated using light and scanning electron micrographs and are compared with similar taxa worldwide. Additionally, two populations of Psammothidium germainii lacking a raphe on the raphevalve are illustrated and discussed.