Visit us at

Diatoms of the United States is now known as Diatoms of North America.
This site has been redesigned and updated, and will be closing soon.

Asterionella ralfsii var. americana

Körner 1970      Category: Araphid

Asterionella formosa


Aulacoseira alpigena

LM scalebar = 10 µm = 40 pixels.


Contributor: David R.L. Burge | Mark Edlund - June 2017
Length Range: 105-192 µm
Width Range: 1.5 to 2.8 at the valve center µm
Striae in 10 µm:


Valves heteropolar and linear. Headpole is capitate and ends bluntly truncated, 3.1 to 3.7 µm wide. Foot pole is rostrate, ending rounded, 1.3 to 1.6 µm wide, not as wide as the valve center. Rimoportulae present in the headpole. Striae very fine, not easily resolved in LM. Spines can be faint in LM, occurring at the valve margin 6 to 7 in 10 µm. In girdle view, the head pole is expanded in the pervalvar axis.

Original Description

Author: Körner 1970
Length Range: 20-90 µm
Width Range: 1-5 µm
Striae in 10 µm: 30

Original Description

It differs from the nominate variety and the other variety by the triangular shaped foot pole, the smaller transapical width in the middle of the valve and by the distinct geographical distribution; besides to be distinguished by means of the electronic microscope by the broad pseudoraphe.

Original Images

Cite This Page:
Burge, D., and Edlund, M. (2017). Asterionella ralfsii. In Diatoms of the United States. Retrieved May 25, 2018, from

Species: Asterionella ralfsii

Contributor: David R.L. Burge | Mark Edlund

Reviewer: Becky Bixby


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.

Körner, H. (1970). Morphologie und Taxonomie der Diatomeen Gattung Asterionella. Nova Hedwigia 20: 557-724.

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)

Asterionella ralfsii var. americana CAS

North American Diatom Ecological Database (NADED)

NADED ID: 9002

Autecology Discussion

This taxon is commonly found in the plankton forming stellate colonies in northern, low pH lakes and ponds of the northeastern United States (Körner 1970, Camburn and Charles 2000, Siver et al. 2005) and Canada (Fallu et al. 2000). Here we observed A. ralfsii var. americana from Partridge Lake in the Boundary Waters Canoe Area Wilderness of northern Minnesota.