• Category
  • Length Range
    23-47 µm
  • Width Range
    7.1-9.4 µm
  • Striae in 10 µm
    12-16 at the valve center, 16-20 near the ends
  • Reported As
    Cymbella subaequalis (Patrick and Reimer 1975, p. 24, plate 3, figs. 13-14)



Valves are lanceolate to elliptic-lanceolate and somewhat dorsiventral. The dorsal and ventral margins are arched and taper to obtusely rounded, subtly protracted apices. The axial area is narrow and widens gradually from the apices toward the central area. The central area is small and irregular, barely wider than the axial area. The raphe is lateral and narrows toward the proximal and distal ends. Proximal raphe ends are deflected ventrally and slightly expanded. Distal raphe fissures are semicircular and deflected dorsally. Striae are radiate throughout and indistinctly punctate. Areolae number 30-38 in 10 µm.


There are 45 records for C. subaequalis in the Montana Diatom Database from northwestern Montana, northern Idaho, and southwestern Alberta. The species is especially common and widespread in the Canadian Rockies ("Crown of the Continent") Ecoregion, where it prefers cold, oligotrophic, and somewhat alkaline waters with low to moderate specific conductance. Krammer (2003) reports this species as cosmopolitan in temperate and colder regions in both the northern and southern hemispheres.

L  Josephine
Credit: Loren Bahls
Lake Josephine, Glacier National Park, Montana: home of Encyonema ventricosum

Original Description

  • Basionym
    Cymbella subaequalis
  • Author
    Grunow in Van Heurck 1880

Original Images

Cymbella subaequalis orig illus
Cymbella Subaequalis  Descr

EMAP Assessment

EMAP Distribution

Cymbella Subaequalis  Grunow 40
Map 40

Response Plots

Cymbella Subaequalis  Grunow

Cite This Page

Bahls, L. (2012). Cymbopleura subaequalis. In Diatoms of North America. Retrieved June 17, 2018, from https://diatoms.org/species/cymbopleura_subaequalis


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