• Category
  • Length Range
    19.6-43.5 µm
  • Width Range
    7.5-9.0 µm
  • Striae in 10 µm
    12-14 in the valve center, up to 16 near the apices
  • Reported As
    Cymbella amphicephala (Hustedt 1944 in Schmidt et al. 1874-1959, figs 377: 31-34)



Valves are lanceolate, slightly dorsiventral and subtly triundulate with apiculate to rostrate apices. The dorsal margin is arched; the ventral margin is more weakly arched to almost straight. The axial area is narrow and linear-lanceolate, narrower at the ends and widening gradually to merge with a reduced and irregular central area. The central area that is barely wider than the axial area, or maybe wanting altogether. The raphe is weakly lateral and becomes filiform toward the proximal and distal ends. Proximal raphe ends are weakly expanded and tipped towards the ventral margin. Distal raphe ends are deflected dorsally. Striae are weakly radiate throughout and very finely punctate. Areolae in the striae number about 35 in 10 µm.


Cymbopleura frequens prefers oligotrophic to mesotrophic waters with moderate electrolyte content (Krammer 2003). The specimens shown here are from streams in western South Dakota (images 1-5) and Glacier National Park, Montana (image 6).

Original Description

Valves not or only very slightly dorsiventral, subelliptical-lanceolate, dorsal and ventral margins moderately arched, ends apiculate to rostrate protracted. Length 14-38 µm, breadth 6.4-8.8 µm, maximum length/breadth ratio 4.8. Axial area narrow, linear, narrowing slightly towards the ends, almost in the median line of the valve. Central area an irregular, asymmetric space of different extent. Raphe slightly lateral, narrowing towards the proximal and distal ends. Proximal raphe ends slightly expanded and somewhat ventrally tipped, terminal fissures comma-shaped and dorsally deflected. Striae slightly radiate throughout, irregularly arranged around the central nodule, indistinctly punctate-lineate. Striae in the middle portion (dorsal) 11-14/10 µm, up to 15/10 µm towards the ends, puncta 30-36 (40)/10 µm.

  • Author
    Krammer 2003
  • Length Range
    14.0-38.0 µm
  • Width
    6.4-8.8 µm
  • Striae in 10µm
    11-14 at the valve center, up to 15 near the apices

Original Images

Cymbopleura frequens orig illus 3
 Cymbopleura frequens orig descr

Cite This Page

Bahls, L. (2015). Cymbopleura frequens. In Diatoms of North America. Retrieved July 19, 2024, from https://diatoms.org/species/cymbopleura_frequens


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