On some Psammothidium species from rivers in the United States

Psammothidium species have wide distribution in the US, co-occur on sandy habitats, and overlap in morphology. Samples from rivers and streams were collected as part of the NAWQA program (U.S. Geological Survey). The following species were included in this study: Psammothidium bioretii (Germain) Bukhtiyarova et Round, P. chlidanos (Hohn et Hellerman) Lange-Bertalot, P. grischunum f. daonensis (Lange-Bertalot) Bukhtiyarova et Round, P. helveticum (Hustedt) Bukhtiyarova et Round, and P. subatomoides (Hustedt) Bukhtiyarova et Round. Several morphological characteristics of the valves are outlined. These features are visible with light microscopy (LM) and should be used in routine microscopic identification.