The rare boreo-alpine, oligotraphenic diatom Planothidium distinctum (= Achnanthes distincta) was first described from the western Alps in 1954. Achnanthes hirta, a species described in 1970 from the Pyrenees, is regarded as a heterotypic synonym of Planothidium distinctum but almost all morphological details of P. distinctum are known from the type material of Achnanthes hirta. On the basis of...
