SMALL PLANOTHIDIUM ROUND ET BUKHTIYAROVA (BACILLARIOPHYCEAE) TAXA RELATED TO P. DAUI (FOGED) LANGE-BERTALOT FROM THE UNITED STATES

Abstract

Small species of the genus Planothidium are difficult to identify using light microscopy (LM) due to similarities in valve outline and other structural features. In recent years, application of scanning electron microscopy (SEM) techniques has allowed the distinction and clarification of taxonomie boundaries among several of these taxa, but some taxonomic confusion still remains unresolved in the literature. The present work focuses on species found in samples from U.S. streams and rivers and presents three new combinations (Planothidium conspicuum (Mayer) Morales, Planothidum lemmermannii (Hustedt) Morales, and P. minutissimum (Krasske) Morales) and morphological details and discussions based on literature for two additional species (Planothidium daui (Foged) Lange-Bertalot and Planothidium granum (Hohn et Hellerman) Lange-Bertalot).