• Category
  • Length Range
    38-75 µm
  • Width Range
    12-19 µm
  • Striae in 10 µm
    13-21 in the valve center, 17-21 at the ends
  • Synonyms
    Navicula cuspidata var. ambigua (Ehrenb.) Cleve 1894



There are three valve types found for this taxon: vegetative, “heribaudii”, and craticula forms. The three forms are produced as a cellular strategy for suriving inimical conditions such as desiccation (Schmid 1979). Two craticula are formed within the vegetative frustule and subsequently the “heribaudii” cell is formed within the craticula. The heribaudii cell usually has different ornamentation compared to vegetative cell.

Valves are lanceolate, with protracted rostrate ends. The axial area is narrow and linear. The central area is only very slightly enlarged around the center. The raphe is filiform. The proximal raphe ends are slightly expanded. Striae are slightly radiate, becoming convergent at the ends. Striae may be slightly denser on one side of the valve as compared to the other side. Stria density increases as the size range decreases in this taxon.

In Europe, a greater range in size is reported (length 42-95 µm, breadth 13-24 µm, and striae count 15-18 in 10 µm) (Lange-Bertalot 2001).


Craticula ambigua has been documented in alkaline wetlands and streams of Iowa, including Wickiup Hills (near Cedar Rapids) and Dugout Creek (Dickinson County).

Crat Ambig  Win R 6 28 2012  F2012B 050
Credit: Stephen Main
Valve view of living C. ambigua from the Winnebago River, Iowa.
Crat Ambig  Win R 6 28 2012  F2012B 053
Credit: Stephen Main
Girdle view of living C. ambigua from the Winnebago River, Iowa.
Ill 5 31 12 013  Crat Amb Crather  L  U24 70
Credit: Stephen Main
Craticula and heribaudii internal valves (Iowa Lakeside Lab Diatom Herbarium L-U24 70).

Original Description

N. ambigua, testula a dorso lineari-oblonga utroque apice constricto brevi tenui obtuso. Icon! Priori similis; an pulli Pinnulariae dicephalae?

  • Basionym
    Navicula ambigua
  • Author
    Ehrenb. 1843

Original Images

N Ambigua Orig Illus
N Ambig Orig Des

Cite This Page

LaLiberte, G., Vaccarino, M., Main, S. (2015). Craticula ambigua. In Diatoms of North America. Retrieved June 13, 2024, from https://diatoms.org/species/craticula_ambigua


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