REVISION OF THE GENUS<i>ACHNANTHES SENSU LATO. PSAMMOTHIDIUM</i>, A NEW GENUS BASED ON<i>A. MARGINULATUM</i>

Abstract

This paper concerns a revision of some Achnanthes subsection Achnanthidium or genus Achnanthidium species, common on sand grains in freshwaters. The taxonomy of the species required a scanning electronmicroscopy study of new and old material and examination of some type material. The SEM study has provided illustrations of 18 species, some previously unpublished. A new genus Psammothidium is split off Achnanthidium Kütz. and 25 new combinations made for species and infraspecific taxa. One species Psammothidium bristolicum Bukht. is also described from the River Spey, Scotland. Short comments are provided to assist in the identification of each taxon.