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Aulacoseira ambigua

(Grunow) Simonsen 1979      Category: Centric
BASIONYM: Melosira crenulata var. ambigua Grunow in Van Heurck 1882
SYNONYM(S): Melosira ambigua (Grunow in Van Heurck) O.Müll. 

Aulacoseira alpigena


Aulacoseira canadensis

LM scalebar = 10 µm = 40 pixels.


Contributor: Marina Potapova | Jonathan English - December 2010
Diameter: 3-12 µm
Mantle Height: 5-15 µm
Rows of areolae in 10 µm: 17-22


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

Basionym: Melosira crenulata var. ambigua
Author: Grunow in Van Heurck 1882
Diameter: µm
Rows of areolae in 10 µm:

Original Description

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

Original Images

Cite This Page:
Potapova, M., and English, J. (2010). Aulacoseira ambigua . In Diatoms of the United States. Retrieved May 24, 2018, from

Species: Aulacoseira ambigua

Contributor: Marina Potapova | Jonathan English

Reviewer: Mark Edlund


Kobayasi, H. and Nozava, M. (1981). Fine structure of the fresh water centric diatom Aulacoseira ambigua (Grun.) Sim. Japanese Journal of Phycology 29: 121-128.

Le Cohu, R. (1991). Morphologie des valves et du cingulum chez Aulacoseira ambigua (Grun.) Simonsen (Bacillariophycées). Quelques observations sur les phases pré- et postauxospores. Nova Hedwigia 53:409-421.

Likhoshway, Y.V. and Crawford, R.M. (2001). The rimoportula — a neglected feature in the systematics of Aulacoseira. E. Economou-Amilli (ed.). Proceedings of the 16th International Diatom Symposium. Amvrosiou Press, Athens, Greece.

Simonsen, R. (1979). The diatom system: ideas on phylogeny. Bacillaria 2: 9-71.

Siver, P.A. and Kling, H. (1997). Morphological observations of Aulacoseira using scanning electron microscopy. Can. J. Bot. 75: 1807–1835.

Links & ID's

Index Nominum Algarum (INA)

Original INA

California Academy of Sciences (CAS)

Aulacoseira ambigua CAS

NCBI Genbank Taxonomy

Aulacoseira ambigua NCBI
Melosira ambigua NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 10008

Autecology Discussion

EMAP Assessment

The Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Over 1200 streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Aulacoseira ambigua

EMAP Response Plots

Aulacoseira ambigua

EMAP citations

Results are published in:

Johnson, T., Hermann, K., Spaulding, S., Beyea, B., Theel, C., Sada, R., Bollman, W., Bowman, J., Larsen, A., Vining, K., Ostermiller, J., Petersen, D. Hargett, E. and Zumberge, J. (2009). An ecological assessment of USEPA Region 8 streams and rivers. U.S. Environmental Protection Agency Region 8 Report, 178 p.

Stoddard, J. L., Peck, D. V., Olsen, A. R., Larsen, D. P., Van Sickle, J., Hawkins, C. P., Hughes, R. M., Whittier, T. R., Lomnicky, G. A., Herlihy, A. T., Kaufman, P. R., Peterson, S. A., Ringold, P. L., Paulsen, S. G., and Blair, R. (2005). Environmental Monitoring and Assessment Program (EMAP) western streams and rivers statistical summary. U.S. Environmental Protection Agency Report 620/R-05/006, 1,762 p.

Stoddard, J. L., Peck, D. V., Paulsen, S. G., Van Sickle, J., Hawkins, C. P., Herlihy, A. T., Hughes, R. M., Kaufman, P. R., Larsen, D. P., Lomnicky, G. A., Olsen, A. R., Peterson, S. A., Ringold, P. L., and Whittier, T. R. (2005). An ecological assessment of western streams and rivers. U.S. Environmental Protection Agency Report 620/R-05/005, 49 p.