• Category
  • Length Range
    172.7-297.0 µm
  • Width Range
    39.3-64.0 µm
  • Striae in 10 µm
  • Reported As
    Pinnularia dactylus (Patrick and Reimer 1966, p. 632, plate 62, fig. 4)
    Pinnularia dactylus (Krammer and Lange-Bertalot 1986, p. 430, fig. 198: 1)



Valves are large and linear-elliptic with slightly convex margins and rounded apices. The post-initial valves are tumid in the center. The central area is asymmetric and rounded. The raphe is distinctly lateral and complex (a raphe with an extremely curved outer fissure). Proximal raphe ends are deflected to one side and terminate in small pores. Terminal raphe fissures are S-shaped, or bayonet-shaped depending on the depth of focus. Striae are radiate at the valve center, becoming parallel near the apices. Striae are crossed by a broad longitudinal line. The proximal edge of this band is distinct.


The specimens of P. gigas pictured on this website are from two small ponds and a fen in Glacier National Park, Montana. In these waters, pH ranges from 6.02 to 7.34 and specific conductance from 31 to 71 µS/cm. Krammer (2000) reports this species from nordic-alpine regions in oligotrophic waters with low electrolyte content and low pH.

Atlantic  Pond  Gnp
Credit: Loren Bahls
Atlantic Pond, Glacier National Park, Montana: home of Pinnularia gigas.

Original Description

  • Author
    Ehrenb. 1843

Cite This Page

Bahls, L. (2014). Pinnularia gigas. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/pinnularia_gigas


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