• Category
  • Length Range
    42.5-69.7 µm
  • Width Range
    7.7-10.6 µm
  • Striae in 10 µm



Valves are linear with triundulate margins. In the largest specimens, the central undulation is wider than the distal undulations. Apices are distinctly capitate. Axial areas are about one-third the valve width and become wider from the apices towards the valve center. The central area is a bilateral fascia. The surface of the valve is mottled along either side of the raphe, continuing into the central area. The raphe is straight. 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.


The specimens of P. nodosa var. percapitata observed are from streams, ponds and small lakes in the northern Rocky Mountains of Montana. At these locations pH ranged from 6.10 to 7.78 and specific conductance ranged from 22 to 169 µS/cm. Water quality preferences of this variety appear to be similar to those of the nominate variety: low to moderate electrolyte content and low pH, most commonly found in peaty bogs and in springs (Krammer 2000).

Drosera  Pond
Credit: Loren Bahls
Drosera Pond at Indian Meadows Research Natural Area, Helena National Forest, Montana.

Original Description

  • Author
    Krammer 2000
  • Length Range
    47-61 µm
  • Width
    9-10 µm
  • Striae in 10µm

Original Images

Pinnularia Nodosa Percapitata Origdesc2002
Pinnularia Nodosa Percapitata Origimag1001
Pinnularia Nodosa Percapitata Origimag2002
Pinnularia Nodosa Percapitata Origdesc1001

Cite This Page

Bahls, L. (2014). Pinnularia nodosa var. percapitata. In Diatoms of North America. Retrieved May 29, 2024, from https://diatoms.org/species/pinnularia_nodosa_var._percapitata


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