• Category
  • Length Range
    68-80 µm
  • Width Range
    8.9-10.3 µm
  • Striae in 10 µm



Valves are rhombic-lanceolate with a triundulate outline, the middle expansion is wider than the distal ones. Apices are capitate and rounded. The axial area is very wide and lanceolate in shape. The central area is a transverse fascia. In some populations, there are one or two short striae on the secondary side of the fascia. The raphe is lateral. Proximal raphe ends are curved to the primary side. Terminal raphe fissures are shaped like question marks. Striae are very short and radiate in the middle, becoming longer and strongly convergent towards the apices.

With their shorter striae, less swollen middles, and broad axial areas with distinct markings, the specimens pictured above belong to P. polyonca var. stidolphii. Thanks to Paul Hamilton for this observation.


Pinnularia polyonca has been found in two small lakes and a floating-mat fen in western Montana. All three sites have abundant vascular plant growth. The pH of these sites ranges from 6.73 to 7.41 and specific conductance ranges from 22 to 257 µS/cm.

Skinner  Lake
Credit: Loren Bahls
Skinner Lake, Beaverhead National Forest, Montana: home of Pinnularia polyonca.

Original Description

  • Basionym
    Navicula polyonca
  • Author
    Bréb. in Kütz. 1849

Original Images

Pinnularia Polyonca  Descr

Cite This Page

Bahls, L. (2012). Pinnularia polyonca. In Diatoms of North America. Retrieved June 22, 2021, from https://diatoms.org/species/pinnularia_polyonca


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