• Category
  • Length Range
    28-76 µm
  • Width Range
    1.9-2.9 µm
  • Striae in 10 µm
  • Synonyms
    Fragilaria incognita Reichardt



Valves are lightly silicified, linear, and very narrow with capitate apices. The central sternum is barely visible in LM. Transapical costae are irregularly spaced and number 11-17 in 10 µm. Striae are faint and also irregularly spaced.


Cells of Distrionella incognita may be solitary or form stellate, zig-zag, or ribbon-like colonies. It has two long flat plastids, one on either side of a central nucleus. It is benthic, but may appear incidentally in the plankton. In the United States its range is largely limited to the Canadian Rockies ("Crown of The Continent") ecoregion in northwestern Montana and to rivers (e.g. Kootenai River in northern Idaho) whose headwaters are in this ecoregion. Here it is found in lakes and streams with alkaline pH (range 7.3-8.6) and moderate levels of electrolytes (specific conductance range 222-616 µS/cm).

Distrionella incognita
Credit: Loren Bahls
Stellate colony of Distrionella incognita from Birch Creek, Pondera County, Montana.

Original Description

Schalen schmal lanzettlich bis linear-lanzettlich mit schwach bis mäβig kopfig gerundeten Enden, 50-85 µm lang, 1,8-3 µm breit. Transapikalstreifen sehr zart und unregelmäβig gestellt, 22-28 in 10 µm. Im LM fallen nur die unregelmäβig breiten Zwischenräume zwischen den Areolen reihan auf. Axialarea sehr eng und im LM kaum erkennbar, Zentralarea fehlt. In der Nähe eines Schalenpols befinder sich ein Lippenfortsatz.

  • Basionym
    Fragilaria incognita
  • Author
    E.Reichardt 1988
  • Length Range
    50-85 µm
  • Width
    1.8-3.0 µm
  • Striae in 10µm

Original Images

Fragilaria incognita orig illus
Distincog Origdesc

Cite This Page

Bahls, L. (2012). Distrionella incognita. In Diatoms of North America. Retrieved June 23, 2024, from https://diatoms.org/species/distrionella_incognita


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