New or rare species of cymbelloid diatoms (Bacillariophyceae) from Colorado (USA)

Abstract

The cymbelloid diatoms of the Rocky Mountain region of the United States are not well known, with only a few species having been reported. Collections of diatoms from Rifle Falls in Garfield County, Colorado, USA, contain a wide range of cymbelloid diatom diversity. The collections include a new species of Cymbella, C. subtravertiensis sp. nov., belonging to the Cymbella helvetica group, which lacks apical pore fields. In addition, a rare species of Encyonopsis originally documented from Austria is also present, for which we include the first published electron microscope study of its valve morphology; this is the first report of this species in the United States. In addition, three new species of Encyonopsis, including E. coloradensis sp. nov., E. rockiensis sp. nov., and E. riflensis sp. nov. are documented with light and scanning electron microscopy, and these species provide excellent examples of the subtle morphological differences that can exist within the genus with regard to the morphology of the areolae and alveoli. Finally, we document a new species of Encyonema, E. calcephila sp. nov., that is similar to E. hustedtii, a species from Java.