• Category
  • Diameter
    13.0-25.6 µm
  • Striae in 10 µm
    Fascicles 3-4
  • Synonyms
    Cyclotella oregonica (Ehrenb.) Ralfs in A.Pritch. 1861
  • Reported As
    Stephanodiscus oregonica (Håkansson and Kling 1989)
    Stephanodiscus excentricus (Hustedt 1952 pg 378, figs 37-38)



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.

The circumferential density of fascicles is 3-4 in 10 µm.

Scanning electron micrographs and observations of S. oregonicus were published by Håkansson (2002).

Stephanodiscus excentricus Hust. was described from fossil material collected in Oregon and in my view, S. excentricus conforms to the type of S. oregonicus.

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).


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  Mc Donald  May 10 2007
Credit: Glacier National Park webcam
Lake McDonald, Glacier National Park, Montana: home of Stephanodiscus oregonicus.

Original Description

  • Basionym
    Discoplea oregonica
  • Author
    Ehrenb. 1854

Citations & Links



  • Index Nominum Algarum
  • North American Diatom Ecological Database
    NADED ID: 64035

Cite This Page

Bahls, L. (2013). Stephanodiscus oregonicus. In Diatoms of North America. Retrieved April 16, 2024, from https://diatoms.org/species/stephanodiscus_oregonicus


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Stephanodiscus oregonicus from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.