• Category
  • Length Range
    31-70 µm
  • Width Range
    3.2-7.3 µm
  • Striae in 10 µm
  • Synonyms
    Synedra cyclopum Brutschy 1922



Valves are linear to linear-lanceolate and arcuate, with gradually attenuated subcapitate ends. The axial area is linear and very narrow, widening near the central area. The central area is longer than broad, extends to the valve margins, and often contains ghost striae. The central area is not swollen and may be slightly indented on the concave side of the valve in smaller specimens. Areolae in the striae are indistinct in LM.


This taxon is uncommon and widely dispersed in the plankton of lakes and reservoirs (and in streams below lakes and reservoirs) in the western United States. Patrick and Reimer (1966) report that it is often attached to crustacea in cool water. In Europe, Krammer and Lange-Bertalot (1991) report it from lakes of medium electrolyte content, where it lives, attached, to copepods.

Gates Of The  Mountains
Credit: Loren Bahls
Gates of the Mountains on the Missouri River below Hauser Dam, Lewis and Clark County, Montana: home of Synedra cyclopum.

Original Description

  • Author
    Brutschy 1922

Original Images

Synedra Cyclopum Orig Desc


Aug 10, 2023 - Transfer from Synedra to Fragilaria

From June 2012 until August 2023, this taxon appear as Synedra cyclopum Bruschy 1922. Recent work (Van de Vijver et al. 2021) to examine the taxon and designate a lectotype supported its position in the genus Fragilaria. - S. Spaulding

Cite This Page

Bahls, L. (2012). Fragilaria cyclopum. In Diatoms of North America. Retrieved June 19, 2024, from https://diatoms.org/species/fragilaria_cyclopum


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