• Category
  • Length Range
    34-65 µm
  • Width Range
    14-26 µm
  • Striae in 10 µm
    7-10 in the valve center, 12-17 near the apices
  • Reported As
    Eunotia serra var. diadema (Krammer and Lange-Bertalot 1991)
    Eunotia serra var. diadema (Patrick and Reimer 1966)



Valves are highly arched. The dorsal margin has a constant 6 bluntly pointed undulations. The ventral margin is concave and follows the same curvature as the dorsal margin. The apices are wider than the undulations and obtusely rounded. Apices are set off from (never coalesce with) the terminal undulations, even in smaller specimens. Distal raphe ends lie along the valve face very close and parallel to each end. Striae are radiate throughout and of two types: complete striae that extend the full width of the valve and short striae that occur only along the dorsal margin. Fan-shaped packets of short striae fill the gaps between complete striae within each undulation. A fine transparent line runs close and parallel to the ventral margin. Striae on either side of this line may be continuous or displaced. Areolae in the striae are easily resolved in LM and number 20-23 (mostly 22) in 10 µm.

The specific epithet diadema is the Latin word for "crown".


In the Montana Diatom Collection, Eunotia diadema occurs in fens, ponds and small lakes, primarily in the Idaho Batholith and Canadian Rockies ecoregions of western Montana. These waters typically have circumneutral to somewhat acidic pH and low conductivity. Patrick & Reimer (1966) combine this taxon with Eunotia tetraodon and report them as occurring in oligotrophic or dystrophic swamps and bogs in the New England states and Utah. Lange-Bertalot et al. (2011) report it as a component of the Holarctic flora where it is associated with other acidophilous diatoms.

Paradise  Pond And  Rising  Wolf  Mountain 3
Credit: Loren Bahls
Paradise Pond, Glacier National Park, Montana: home of Eunotia diadema.

Original Description

  • Author
    Ehrenb. 1837

Cite This Page

Bahls, L. (2012). Eunotia diadema. In Diatoms of North America. Retrieved July 19, 2024, from https://diatoms.org/species/eunotia_diadema


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