Contributor: Loren Bahls - April 2016
Length Range: 10-23 µm
Width Range: 6.0-9.6 µm
Striae in 10 µm: 10-12 at the valve center
Valves are elliptic with cuneate apices. The raphe is straight and filiform with slightly expanded proximal ends. The axial area is narrow and linear. The central area is small and elliptic, and a small stigma appears to be present. Striae are uniseriate and radiate. Striae at the center of the valve are more widely spaced than striae near the apices. The round to apically elongate areolae are coarse, visible under LM, and number 28-36 in 10 µm. Two to four pairs of annulae are present at the apices.
With two to four pairs of annulae at each apex, this taxon clearly belongs in the genus Geissleria and should be considered for nomenclatural transfer. This taxon differs from other species of Geissleria in North America by the coarse areolae. SEM examination is needed to confirm the presence of a stigma.
Basionym: Navicula cascadensis
Author: Sovereign 1958
Length Range: 11-21 µm
Width Range: 6-9 µm
Striae in 10 µm: 9-11
Kulikovskiy, M.S., Lange–Bertalot, H., Metzeltin, D. and Witkowski, A. (2012). Lake Baikal: Hotspot of endemic diatoms I. Iconographia Diatomologica, Vol. 23 (Lange–Bertalot, H., ed.) Koeltz Scientific Books. Koenigstein , pp. 7–607.
Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.
Sovereign, H.E. (1958). The diatoms of Crater Lake, Oregon. Transactions of the American Microscopical Society 77(2):96-134.
Navicula cascadensis is endemic to the Cascade Mountains of western Oregon. Here it lives in lakes and streams with low electric conductivity (24-38 µS/cm) and slightly acid pH (6.70-6.93).
Snow Creek, Deschutes County, Oregon: home of Navicula cascadensis
Credit/Source: Kirsten Gallo, U. S. Forest Service