Fragilaria holstonensis (Bacillariophyceae: Fragilariaceae), a new species of needle-shaped diatom from a pond in the Appalachian Mountains of Virginia, U.S.A.

A new freshwater diatom, Fragilaria holstonensis sp. nov., was collected from the suspended plankton of a manmade, artificially aerated alkaline pond located in the Valley and Ridge physiographic region of the Appalachian Mountains. The morphological features of F. holstonensis were analysed using light and scanning electron microscopy. Fragilaria holstonensis is characterized by primarily solitary cells, as two connected valves were occasionally observed. Valves are thin, linear-lanceolate, with a broader central area tapering gradually towards subcapitate to capitate apices. Striae alternate from 18–22 in 10 µm. Areolae are not visible with light microscopy. Fragilaria holstonensis can be distinguished from other needle-like species of Fragilaria due to differences in valve morphology, stria density and the structure of the apical pore field. The genetic marker, rRNA 18S SSU (nucleus), was sequenced, and its closest relative was determined to be an unnamed Fragilaria sp., which differed from F. holstonensis by 4 nucleotides.