• Category
  • Length Range
    20.0-68.0 µm
  • Width Range
    3.0-5.0 µm
  • Synonyms
    Nitzschia sigma var. clausii (Hantzsch) Grunow



In girdle view, the frustules are distinctly sigmoid. Valves are linear and slightly concave at the center. The apices are distinctly rounded, capitate or rostrate and bent to form a sigmoid valve shape. The striae are very fine. The keeled raphe is distinct, with robust fibulae. Fibula density is 10-13 in 10 µm.

Krammer and Lange-Bertalot (1988, Plate 19, Figs 1-6A) illustrate longer specimens of this species (e.g. Fig. 5) that are narrower than the shorter specimens (e.g. Fig. 1), suggesting that more than one taxon might be included in their concept of the species.

Original Description

  • Author
    Hantzsch 1860

Original Images

N Clausii Orig Descr Plate
N Clausii Orig Descr Text

Cite This Page

Kociolek, P. (2011). Nitzschia clausii. In Diatoms of North America. Retrieved July 24, 2024, from https://diatoms.org/species/nitzschia_clausii


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