Eunotia bidentula

W.Sm. 1856      Category: Eunotioid
SYNONYM(S): Eunotia tridentula var. bidentula  (W.Sm.) Hérib. 1893 | Eunotia diodon f. bidentula (W.Sm.) Åke Berg 1945 

Eunotia bidens


Eunotia bilii

LM scalebar = 10 µm = 80 pixels.


Contributor: Ian Bishop | David R.L. Burge | Lynn Brant - August 2016
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


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.

Original Description

Author: W. Smith 1856
Length Range: 20-38 µm
Striae in 10 µm: 16.5

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.

Original Images

Cite This Page:
Bishop, I., Burge, D., and Brant, L. (2016). Eunotia bidentula. In Diatoms of the United States. Retrieved April 19, 2018, from

Species: Eunotia bidentula

Contributor: Ian Bishop | David R.L. Burge | Lynn Brant

Reviewer: Sarah Spaulding


Camburn, K.E. and Charles, D.F. (2000). Diatoms of Low-Alkalinity Lakes in the Northeastern United States. Academy of Natural Sciences of Philadelphia, Special Publication 18, 152 pp.

Fallu, M.-A., Allaire, N. and Peinitz, R. (2000). Freshwater diatoms from northern Québec and Labrador (Canada). Species-environment relationships in lakes of boreal forest, forest-tundra and tundra regions. Bibliotheca Diatomologica 45: 1-200.

Gaiser, E.E. and Johansen, J. (2000). Freshwater diatoms from Carolina bays and other isolated wetlands on the Atlantic Coastal Plain of South Carolina, USA, with descriptions of seven taxa new to science. Diatom Research 15(1): 75-130. 10.1080/0269249X.2000.9705487

Krammer, K. and Lange-Bertalot, H. (1991). Bacillariophyceae. 3. Teil: Centrales, Fragilariaceae, Eunotiaceae. In Ettl, H., Gerloff, J., Heynig, H. & Mollenhauer, D. (Eds.). Süsswasserflora von Mitteleuropa. 2(3): 1-576. Gustav Fisher Verlag, Stuttgart, Germany.

Lange-Bertalot, H., Bak, M., Witkowski, A. and Tagliaventi, N. (2011). Eunotia and some related genera. Diatoms of the European Inland Waters and Comparable Habitats. 6: 747 pp.

Patrick, R.M. and Reimer, C.W. (1966). The Diatoms of the United States exclusive of Alaska and Hawaii, V. 1. Monographs of the Academy of Natural Sciences of Philadelphia 13.

Siver, P.A. and Hamilton, P.B. (2011). Diatoms of North America: The Freshwater Flora of Waterbodies on the Atlantic Coastal Plain. Iconographia Diatomologica 22.

Siver, P.A., Hamilton, P.B., Stachura-Suchoples, K. and Kociolek, J.P. (2005). Diatoms of North America. The Freshwater Flora of Cape Cod. Iconographia Diatomologica 14: 1-463.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Eunotia bidentula CAS

North American Diatom Ecological Database (NADED)

NADED ID: 33004

Autecology Discussion

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.


Littoral zone sphagnum mat at Kings Lake Bog

Credit/Source: Ian Bishop

Shoreline of Kings Lake Bog

Credit/Source: Ian Bishop