• Category
  • Diameter
    18.1-48.2 µm
  • Striae in 10 µm



Valves are cylindrical with a transversely undulate central area that occupies about half the valve diameter. One or two central fultoportulae are clearly visible in LM on the convex (raised) portion of the central area. The central area is otherwise colliculate with scattered nodules, or is unornamented. Striae are equal in length and multiseriate near the valve margins. Striae become uniseriate nearest to the valve center, where individual areolae are easily distinguished in LM.

Internally, alveoli are partially occluded by a central lamina, creating a distinct concentric ring (also called a shadow line) through the striae about one-third of the distance from the central area to the valve margin. Another concentric ring near the valve margin represents the distal internal occlusions of the alveoli (Håkansson 2002, Houk et al. 2010, Lowe 1981).

This page is dedicated to Rex Lowe on the occasion of his 70th birthday. Lowe published pioneering descriptions of the ultrastructure, ecology, and distribution of Cyclotella gamma over thirty years ago (Lowe 1981). More recently, Håkansson (2002) and Houk et al. (2010) have also published SEM descriptions and images. These images and descriptions were used above to describe features that cannot be seen in LM.


Cyclotella gamma is a resident of the benthos of shallow, weedy, mesotrophic lakes at lower elevations in the northern United States. It was described from a lake on Orcas Island, Washington (Sovereign 1963) and subsequently recorded from several lakes in Michigan (Lowe 1981). The specimens shown on this page are from three lakes in the Northern Continental Divide Ecoregion of Montana. The pH of these lakes ranges from 7.2 to 7.8 and specific conductance ranges from 250 to 332 µS/cm. Cyclotella gamma is probably much more widely distributed than these records indicate because it is often confused with C. meneghiniana.

Hidden Meadow Lake
Credit: Wanderingthewild.com
Hidden Meadow Lake, Glacier National Park, Montana: home of Pinnularia brebissonii.

Original Description

Cells circular, drum-shaped, 18-33 µm in diameter. The marginal zone of the valves has radial costae on the inner side of the membrane (like Pinnularia) 5 to 7 in 10 µm; on the exterior of the membrane are radial rows of poroids upon the interior costae. Openings of the inner compartments of the costae form a small circular band crossing the costae. The median area is about half the diameter of the valve, is tangentially waved and one or more large pores are located at a distance from the center.

  • Author
    Sovereign 1963
  • Length Range
    18-33 µm
  • Striae in 10µm
    5-7 alveoli ("costae")

Original Images

Cyclotella gamma orig desc
Cyclotella gamma orig illus
Cyclotella gamma orig descr1

Citations & Links



Aug 29, 2022 - Transfer to Stephanocyclus

From 12/15/2013 until 8/29/2022, this taxon appeared as Cyclotella gamma Sovereign 1963. Following Kulikovskiy et al. (2022), it is transferred to Stephanocyclus gamma (Sovereign) Kulikovskiy, Genkal and Kociolek 2022. - S. Spaulding

Cite This Page

Bahls, L. (2013). Stephanocyclus gamma. In Diatoms of North America. Retrieved June 20, 2024, from https://diatoms.org/species/stephanocyclus_gamma


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