• Category
  • Length Range
    22-34 µm
  • Width Range
    4.0-8.2 µm
  • Striae in 10 µm
    14-17 at mid-valve; up to 20 at the ends
  • Synonyms
    Eunotia tridentula var. bidentula (W.Sm.) Hérib. 1893
    Eunotia diodon f. bidentula (W.Sm.) Åke Berg 1945



Ventral margin is straight, becoming slightly concave in the smallest specimens. Dorsal margin is distinctly biundulate, with two rounded crests. Apices are slightly protracted, sub-capitate to capitate on the dorsal margin and straight on the ventral margin. Striae are parallel at mid-valve, becoming increasingly radiate and dense toward the poles. Shortened striae are present in the dorsal undulations. The helictoglossae are positioned at the margin of the valve face, and angled toward the apices. Areola density is high but areolae are discernible in LM, measuring 34-36 in 10 µm.


This species is considered to be acidophilic (Lange-Bertalot et al. 2011, Patrick and Reimer 1966). It is rare in Europe, preferring fens and peat bogs of the Holarctic according to Lange-Bertalot et al. (2011). In North America, it has been reported from lakes of northwestern Quebec (Fallu et al. 2000) and is widely reported from acidic lakes and wetlands of the eastern United States (Patrick and Reimer 1966, Camburn and Charles 2000, Gaiser and Johansen 2000, Siver et al. 2005, Siver and Hamilton 2011). The population examined for this page was collected in Kings Lake Bog, a protected, lowland sphagnum bog in the western foothills of the central Cascades of Washington state.

Kings Lake Bog Sphagnum
Credit: Ian Bishop
Littoral zone sphagnum mat at Kings Lake Bog
Kings Lake Bog Shoreline
Credit: Ian Bishop
Shoreline of Kings Lake Bog

Original Description

Frustule direct; valve with two prominent, acute, or rounded dorsal ridges; basal margin straight, extremities produced; striae indistinct, 42 in .001". Length .0008" to .0015". v.v.

  • Author
    W. Smith 1856
  • Length Range
    20-38 µm
  • Striae in 10µm

Original Images

Eunotia Bidentula Orig Desc Text

Citations & Links



  • Index Nominum Algarum
  • North American Diatom Ecological Database
    NADED ID: 33004

Cite This Page

Bishop, I., Burge, D., Brant, L. (2016). Eunotia bidentula. In Diatoms of North America. Retrieved February 29, 2024, from https://diatoms.org/species/eunotia_bidentula


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