• Category
  • Length Range
    27.1-47.6 µm
  • Width Range
    8.0-10.2 µm
  • Striae in 10 µm



Valves are linear to linear-elliptic, with parallel to moderately convex margins. Apices are broadly rounded and not protracted. The axial area is narrow. A large transverse central area is formed by one or two shorter striae on each side. The raphe is filiform, to weakly lateral and straight. Proximal raphe ends are deflected to one side and tipped with expanded pores. Distal raphe ends are sickle-shaped. Striae are broad and widely separated, weakly radiate near the valve center and becoming convergent toward the apices.

Pinnularia borealis encompasses a large infraspecific complex. The nominate variety is pictured and described here. This is the most typical and most common form in the complex.


Pinnularia borealis is a common cosmopolitan species found in aerial habitats (rocks, walls, soil, moss) and flowing and standing waters (Krammer 2000). The specimens pictured and described on this web page are from a variety of habitats in the Northwest United States.

Original Description

  • Author
    Ehrenb. 1843

Cite This Page

Bahls, L. (2014). Pinnularia borealis. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/pinnularia_borealis


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