• Category
  • Diameter
    3-12 µm
  • Width Range
    5-15 µm
  • Striae in 10 µm
  • Synonyms
    Melosira ambigua (Grunow in Van Heurck) O.Müll.



Frustules are cylindrical and form colonies. Valves are 3-12 µm in diameter, with a mantle height of 5-15 µm. The ratio of the mantle height to valve diameter is greater than 1. The mantle has straight sides and the valve face is flat with slightly convex margins.The valve face of most valves do not have areolae, but a single ring of areolae might be found on the valve face of separation valves. The spiral rows of pervalvar areolae are curved to the right (dextrorse) and number 17-22 in 10 µm. The areolae are round to square in shape. Spines are located at the end of each pervalvar costa. Linking spines are short, triangular or bifurcated. Two lobes of the spines are rounded or acute. Separation spines are small and pointed. In some separation valves, rows of areolae coalesce when they approach the valve face, thus giving the appearance of spines originating from two pervalvar costae. The ringleiste is hollow, described in the literature as a "U-shaped sulcus". The valves have two rimoportulae, located at the ringleiste and opposite to one other.

Colonies are usually straight, but sometimes spiral, with curved cells. Such populations have been described as separate forms of A. ambigua (Melosira ambigua f. spiralis Skuja 1948; M. ambigua f. curvata Skabichevskii 1960; M. ambigua f. spiroides Chalfina 1966), but there is no evidence that this trait has taxonomic significance.


Original Description

Se rapprochant en partie de la var. italica et en partie de la var tenuis.

  • Basionym
    Melosira crenulata var. ambigua
  • Author
    Grunow in Van Heurck 1882

Original Images

Orig Ill  Auamb 1
Orig Descr  Auamb 1

EMAP Assessment

EMAP Distribution

Aulacoseira Ambigua 20 Copy
Map 20

Response Plots

Aulacoseira Ambigua Copy

Cite This Page

Potapova, M, and English, J. (2010). Aulacoseira ambigua . In Diatoms of North America. Retrieved June 23, 2018, from https://diatoms.org/species/aulacoseira_ambigua


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