• Category
  • Length Range
    40.9-65.2 µm
  • Width Range
    7.6-9.3 µm
  • Striae in 10 µm



Valves are linear with triundulate margins. The undulations are about equal in width. Apices are subcapitate and rounded. Axial areas are about one-third the valve width and become wider from the apices toward the valve center. The central area is a bilateral, sometimes a unilateral, fascia. A mottled surface of the valve is evident along either side of the raphe and continues into the central area. The raphe is lateral. Proximal raphe ends are bent to one side and terminate in small tear-shaped pores. Distal raphe fissures are shaped like question marks. Striae are weakly radiate at the valve center, becoming strongly convergent at the apices.

Two morphotypes (Krammer 2000) and variety pseudogracillima A. Mayer (1916) are pictured and described here. The morphotype or variety is indicated in the caption of each image. See also the separate page for P. nodosa var. percapitata. The description and images of "P. nodosa" presented by Patrick and Reimer (1966, p. 601, Plate 55, figs. 20, 21) appear to be of another triundulate Pinnularia.


The specimens of P. nodosa observed here are from streams, ponds and small lakes in the Rocky Mountains and Sierra Nevada Mountains of the western United States. At these locations pH ranged from 6.02 to 7.90 and specific conductance ranged from 37 to 71 µS/cm. Krammer (2000) reports this species from waters with a low to moderate electrolyte content and pH less than 5.5, most commonly in peaty bogs and in springs.

Deadfall Lake Ca
Credit: Craig Weiland, Adventurers and Scientists for Conservation.
Deadfall Lake, Trinity County, California: home of Pinnularia nodosa morphotype 2.

Original Description

  • Basionym
    Navicula nodosa
  • Author
    Ehrenb. 1838

Cite This Page

Bahls, L. (2014). Pinnularia nodosa. In Diatoms of North America. Retrieved July 15, 2024, from https://diatoms.org/species/pinnularia_nodosa


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