• Category
  • Length Range
    47-74 µm
  • Width Range
    15-23 µm
  • Striae in 10 µm
    15-18 near valve center, 19-21 near the ends



Valves are moderately arched. The dorsal margin has three broadly rounded undulations, with the number of undulations consistent across large to small valves. The ventral margin is concave and follows the same curvature as the dorsal margin. The apices are protracted, broadly rounded and more narrow than the undulations. Distal raphe ends are curved toward the dorsal margin close to the valve ends. Striae are radiate throughout and are of two types: 1) complete striae that extend the width of the valve and 2) short striae that are interspersed between complete striae along the dorsal margin. A fine hyaline line is near and parallel to the ventral margin. Striae on either side of this line may be aligned or displaced. Areolae in the striae number 27-30 in 10 µm.


Eunotia triodon is uncommon in the Northern Rockies and North Cascades. The specimens shown here are from Blodgett Lake in the Bitterroot Mountains of western Montana and Cutthroat Lake in northern Washington (photos below). Blodgett Lake is at an elevation of 3,000 m. Here pH measured 6.50 and specific conductance was 7 µS/cm.

Blodgett  Lake By Racarlsen 1
Credit: R. A. Carlsen
Blodgett Lake, Bitterroot Mountains, Ravalli County, Montana: home of Pinnularia suchlandtii.
Cutthroat Lake
Credit: Ryan Davis
Adventurers and Scientists for Conservation volunteer Ryan Davis collecting Eunotia triodon at Cutthroat Lake, Washington, July 2013.

Original Description

  • Author
    Ehrenb. 1837

Cite This Page

Bahls, L. (2012). Eunotia triodon. In Diatoms of North America. Retrieved July 20, 2018, from https://diatoms.org/species/eunotia_triodon


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Eunotia triodon 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.