New species and combinations in monoraphid diatoms (family Achnanthidiaceae) from North America

Abstract

This article clarifies the taxonomy and nomenclature of several monoraphid diatom species found in rivers and lakes of North America. The morphology of these diatoms is studied with light and electron microscopy. A new combination Rossithidium anastasiae (Kaczmarska) Potapova is introduced for a species common in both Europe and North America and often misidentified as Achnanthes linearis (W. Smith) Grunow or R. linearis (W. Smith) Round et Bukhtiyarova. Achnanthes harveyi Reimer, often found in eastern North America, is transferred to Psammothidium Bukhtiyarova & Round on the basis of the convex raphe valve, uniseriate striae, and raphe structure. A new Psammothidium species, P. pennsylvanicum Potapova is described and compared with the most similar taxon, P. semiapertum (Hustedt) Aboal. Diatoms originally described as Achnanthes lutheri Hustedt and A. stewartii Patrick are transferred to the genus Platessa Lange-Bertalot on the basis of biseriate striae, flat valves, and the absence of terminal raphe fissures. Two new Platessa species, P. kingstonii Potapova and P. bahlsii Potapova are described from the eastern USA and compared with most similar species, P. lutheri (Hustedt) Potapova and P. conspicua (A. Mayer) Lange-Bertalot, respectively. Achnanthes lanceolata var. abbreviata Reimer, found in the southeastern USA, is shown to possess multiseriate striae and relatively long terminal raphe fissures characteristic for the genus Planothidium Round & Bukhtiyarova, to which it is transferred.

Keywords:

• Achnanthes
• morphology
• Planothidium
• Psammothidium
• Platessa
• Rossithidium
• taxonomy

Acknowledgements

The use of the Centralized Research Facilities, Drexel University, for the SEM is gratefully acknowledged. I am thankful to Friedel Hinz for sending type materials from the Hustedt's Collection, Bremerhaven and to Jonathan English for help with Latin descriptions. This study was supported by the grants WRCP-08286 of the Pennsylvania Department of Conservation and Natural Resources and DBI-0840406 from the National Science Foundation.