• Category
  • Length Range
    86-190 µm
  • Width Range
    30-40 µm
  • Striae in 10 µm
    5-8 near the valve center, 8-12 near the apices
  • Synonyms
    Cymbella inaequalis (Ehrenb.) Rabenh.
  • Reported As
    Cymbella inaequalis (Patrick and Reimer 1975, p. 36, plate 5, fig. 3)



Valves are rhomboid-lanceolate and moderately dorsiventral, with strongly arched dorsal and ventral margins. Apices are bluntly rounded and subrostrate to rostrate. The axial area follows close to the valve midline. The axial area is sub-linear, narrowest near the apices and widening gradually toward the valve middle where it merges with a somewhat wider elliptical central area. The central area is about one-quarter the width of the valve. The raphe is lateral and narrows near the proximal and distal ends. Proximal raphe ends are straight and terminated in expanded pores. Distal raphe fissures are curved, concave toward the dorsal margin. Striae are coarsely punctate and radiate, becoming parallel only very near the apices. Striae tend to be curved toward the valve center. Areolae number 14-22 in 10 µm.


Cymbopleura inaequalis is widely distributed in lakes, ponds, and slow-moving streams across the United States, where it prefers somewhat alkaline waters of moderate conductivity (Patrick and Reimer 1975, Montana Diatom Database). This species has a wider ecological amplitude than most species of Cymbopleura. Because of its large size, this taxon is often overlooked during proportional counts along predetermined transects. It is probably much more widely distributed than records suggest.

Lake  Mc Donald  May 10 2007 1
Credit: National Park Service Webcam Photo
Lake McDonald, Glacier National Park, Montana: home of Cymbopleura inaequalis.

Original Description

  • Basionym
    Navicula inaequalis
  • Author
    Ehrenb. 1838

Cite This Page

Nelson, S, and Bahls, L. (2012). Cymbopleura inaequalis. In Diatoms of North America. Retrieved February 16, 2019, from https://diatoms.org/species/cymbopleura_inaequalis


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