• Category
  • Length Range
    21.7-48.2 µm
  • Width Range
    7.2-12.1 µm
  • Striae in 10 µm
  • Reported As
    Brachysira brebissonii morphotype latior (Lange-Bertalot and Moser 1994, p. 21, Tafel 42:1-4)
    Brachysira brebissonii morphotype major (Lange-Bertalot and Moser 1994, p. 21, Tafel 43:2, 3)
    Navicula serians var. minor (Grunow in Van Heurck 1880, plate XII, fig. 8)



Valves are rhombic with broadly rounded apices. The axial area is narrow and straight, and bordered by a continuous column of areolae on each side. The central area is small and rhombic, sometimes with an enlarged isolated areola on one side. The raphe is filiform. Proximal raphe ends are weakly expanded. Distal raphe ends are difficult to see in LM. Striae are radiate and uniseriate. Areolae in the striae are transapically elliptic near the axial area and linear near the valve margins. Areolae are widely and irregularly spaced, creating a pattern of undulating longitudinal lines.

Note that valves displayed here from the Cascade Mountains in Washington attain a considerably larger size than those originally described from Canada.


Brachysira arctoborealis has been recorded from three lakes in the North Cascade Mountains of Washington. Water quality data are not available, but these lakes are presumed to have cold water, low pH, and low dissolved solids. The species was described from a lake on Baffin Island, Nunavut Territory, and also found in soft-water lakes of the Experimental Lakes Area in western Ontario, Canada (Wolfe and Kling 2001). It was reported by Shayler and Siver (2004) from soft-water lakes in Florida and by Lange-Bertalot ad Moser (1994) from Borneo and the Canadian Rockies (as B. brebissonii morphotype latior and B. brebissonii morphotype major, respectively). Wolfe and Kling (2001) suggest that it is probably a cosmopolitan species, much like B. brebissonii and B. microcephala.

Nada  Lake
Credit: Ryan Davis, Adventurers and Scientists for Conservation.
Nada Lake, Chelan County, Washington: home of Eunotia faba.

Original Description

  • Author
    Wolfe and Kling 2001
  • Length Range
    17-31 µm
  • Width
    7-10 µm
  • Striae in 10µm

Original Images

Brachysira arctoborealis orig illus
Brachysira arctoborealis orig illus 2
Brachysira arctoborealis orig illus 3
Brachysira arctoborealis orig descr

Cite This Page

Bahls, L. (2014). Brachysira arctoborealis. In Diatoms of North America. Retrieved July 21, 2018, from https://diatoms.org/species/brachysira_arctoborealis


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