(Ehrenberg) Håkansson 1986 Category: Centric
BASIONYM: Discoplea oregonica Ehrenberg 1854
SYNONYM(S): Cyclotella oregonica (Ehrenberg) Ralfs in Pritchard 1861
REPORTED AS: Stephanodiscus oregonica (Håkansson and Kling 1989)
Contributor: Loren Bahls - December 2013
Diameter: 13.0-25.6 µm
Rows of areolae in 10 µm:
Valves are cylindrical with strong concentric undulation. The central area is convex or concave, and sometimes slightly off-center. The areolae in the central area are disorganized or arranged in weakly radiate rows. Outside of the central area, fascicles are variable in width, becoming multiseriate near the valve margin. Areolae near the central area are larger than areolae near the margins. Fascicles at the valve margin may include as few as 3 or as many as 9 areolae. A spine is positioned at the distal end of each distinct costa, or interfascicle.
Scanning electron micrographs and observations of S. oregonicus have been published by Håkansson (2002).
In my view, Stephanodiscus excentricus Hustedt refers to the same type as S. oregonicus. Stephanodiscus excentricus Hustedt was described from fossil material collected in Oregon.
Håkansson and Kling (1989) report live specimens of S. oregonicus from Canadian lakes, along with live specimens of S. subtranssylvanicus, although this report deserves further verification. The taxa S. subtranssylvanicus Gasse and S. subtranssylvanicus var. minutula Gasse were described from Ethiopia (Gasse 1980) and such a disjunct distribution ought to be confirmed through examination of the type material. Nevertheless, Håkansson and Kling (1989) reported that smaller forms of S. subtranssylvanicus could not be distinguished from S. oregonicus. They also reported that both species lack valve face fultoportulae and have essentially the same ultrastructure. There is considerable overlap in the reported size ranges of these two taxa: 10-44 µm for S. subtranssylvanicus (Håkansson and Kling 1989) and 6-20.5 µm for S. oregonicus (Håkansson 2002).
Basionym: Discoplea oregonica
Author: Ehrenberg 1854
Rows of areolae in 10 µm:
Ehrenberg, C.G. (1854). Mikrogeologie. Einundvierzig Tafeln mit über viertausend grossentheils colorirten Figuren, Gezeichnet vom Verfasser. Voss, Leipzig., Pl. 5, II, fig. 23 (iconotype).
Gasse, F. (1980). Les diatomées lacustres Plio-Pleistocènes du Gadeb (Ethiopie). Systématique, paléoécologie, biostratigraphie. Revue Algologique, Mémoire hors-série 3: 249 pp.
Håkansson, H. (1986). A taxonomic reappraisal of some Stephanodiscus species (Bacillariophyta). British Phycological Journal 21: 25-37.
Håkansson, H. (2002). A compilation and evaluation of species in the genera Stephanodiscus, Cyclostephanos and Cyclotella with a new genus in the family Stephanodiscaceae. Diatom Research 17: 1-139.
Håkansson, H. and Kling, H. (1989). A light and electron microscope study of previously described and new Stephanodiscus species (Bacillariophyceae) from central and western Canadian lakes, with ecological notes on the species. Diatom Research 4 (2): 269-288.
Hustedt, F. (1952). Neue und wenig bekannte Diatomeen. IV. Botaniska Notiser 1952:366-410.
Krammer, K. and Lange-Bertalot, H. (1991). Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (Eds.). Süsswasserflora von Mitteleuropa. 2(3): 1-576. Gustav Fisher Verlag, Stuttgart, Germany.
Pritchard, A. (1861). A history of infusoria, living and fossil. Edition IV, Whittaker & Co., London, 968 pp.
Stephanodiscus oregonicus was described from fossil material collected in Oregon, but more recently was reported as living in lakes in Canada (Håkansson and Kling 1989). The specimens shown here were collected from macrophytes at a depth of 4 meters near the shore of Lake McDonald in Glacier National Park, Montana (photo below). On the date this sample was collected, pH at the sample site measured 7.10 and specific conductance measured 90 µS/cm. Stephanodiscus oregonicus has also been collected from a pond in Glacier National Park and from Lake Levale, an alpine lake in the nearby Bob Marshall Wilderness.
Lake McDonald, Glacier National Park, Montana: home of Stephanodiscus oregonicus.
Credit/Source: Glacier National Park webcam