• 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 expansion. 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 toward the apices.


This taxon 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

Original Description

  • Author
    Krammer 2000

Original Images

Pinnularia polyonca stidolphii Orig Ill
Pinnularia polyonca stidolphii Orig Descr


Aug 06, 2021 - Correction of identification

From 2012 to 2021, this taxon was appeared as Pinnularia polyonca (Bréb.) W.Smith 1856. I appreciate the comments of Paul Hamilton, who noted that the images are more aligned with P. polyonca var. stidolphii Krammer. The page was updated to make that correction. - S. Spaulding

Cite This Page

Bahls, L. (2012). Pinnularia polyonca var. stidolphii. In Diatoms of North America. Retrieved April 14, 2024, from https://diatoms.org/species/pinnularia-polyonca-stidolphii


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