• Category
  • Length Range
    160.3-256 µm
  • Width Range
    24-31 µm
  • Striae in 10 µm
  • Synonyms
    Navicula torta A.Mann
  • Reported As
    Pinnularia major var. asymmetrica (Cleve 1895 pl. 1 fig. 22)



Valves are linear with rounded ends. Axial area is asymmetrical about apical plane, positioned closer to secondary valve side at the valve ends. Central area is elliptic, slightly wider at the primary valve side. The striae are radiate in the valve center and convergent at the apices where they are longer at the primary valve side than on secondary side. A boundary of the internal alveoli openings is visible in LM as a longitudinal line that is positioned close to axial area. Raphe is lateral. Small spines are present at the valve face-mantle junction.


Pinnularia torta is found in lakes of Eastern United States and Canada. This species is found in a wide range of physico-chemical conditions, including eutrophic and alkaline lakes, but shows some preference towards clear soft water.

Original Description

  • Basionym
    Navicula torta
  • Author
    A.Mann 1924
  • Length Range
    140-260 µm
  • Width
    20-30 µm

Original Images

P Innularia torta Orig Ill 1
Pinnularia torta Orig Descr1

Cite This Page

Kersey, M., Potapova, M. (2022). Pinnularia torta. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/pinnularia-torta


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