• Category
  • Length Range
    17.0-24.6 µm
  • Width Range
    4.0-5.2 µm
  • Striae in 10 µm
  • Reported As
    Anomoeoneis zellensis (Patrick and Reimer 1966, p. 381, plate 33, fig. 14)
    Anomoeoneis brachysira var. zellensis (Camburn and Charles 2000, p. 22, plate 17, figs 46-48)



Valves are linear with parallel sides and bluntly rounded, subrostrate apices. The axial area is narrow. The central area is moderately large and rhombic to elliptic. The raphe is straight. Proximal raphe ends are straight. Distal raphe ends are T-shaped. Striae are weakly radiate. Areolae are transapically elongate. Areolae are transapically elongate and irregularly spaced, creating an undulating longitudinal line on each side of the raphe.

The population shown here does not include larger valves that are typically triundulate with convex margins.


The specimens pictured on this website are from Big Therriault Lake in northwest Montana (photo below). Big Therriault Lake has a pH of 9.05 and s specific conductance of 176 µS/cm. Camburn & Charles (2000) reported B. zellensis from low-alkalinity lakes in New York. Lange-Bertalot & Moser (1994) report this species from temperate and cold regions of the Northern Hemisphere in circumneutral waters with low to moderate electrolyte content.

Big  Therriault  Lake 2
Credit: Loren Bahls
Big Therriault Lake, Ten Lakes Scenic Area, Kootenai National Forest, Montana: home of Brachysira zellensis.

Original Description

  • Basionym
    Navicula zellensis
  • Author
    Grunow 1860

Cite This Page

Bahls, L. (2014). Brachysira zellensis. In Diatoms of North America. Retrieved July 23, 2018, from https://diatoms.org/species/brachysira_zellensis


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