• Category
  • Length Range
    30.0-200.0 µm
  • Width Range
    4.0-13.0 µm
  • Striae in 10 µm



In girdle view, the frustule is distinctly sigmoid. In valve view, depending on the position of the specimen, valves may be distinctly sigmoid. Or, valves may also be linear-lanceolate in the middle of the valve, with the ends curved in opposite directions. The apices are small and capitate. The keel of the raphe is strongly eccentric. Fibula density is 7-12 in 10 µm. Valves lack an expanded central gap in the fibulae.


Original Description

  • Basionym
    Synedra sigma
  • Author
    Kütz. 1844

Original Images


Cite This Page

Kociolek, P. (2011). Nitzschia sigma. In Diatoms of North America. Retrieved June 13, 2024, from https://diatoms.org/species/nitzschia_sigma1


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