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.

Decussata placenta

(Ehrenb.) Lange-Bert. and Metzeltin in Lange-Bert. 2000      Category: Symmetrical biraphid
BASIONYM: Navicula placenta Ehrenb. 1854

Cymbopleura tynnii


Denticula creticola

LM scalebar = 10 µm = 40 pixels.


Contributor: Pat Kociolek - January 2011
Length Range: 24-50 µm
Width Range: 13-18 µm
Striae in 10 µm: 22-27


Valves are elliptic, with rostrate to rostrate/apiculate to capitate/apiculate apices. The axial area is narrow and expanded at the center to form a transapically oval to circular central area. The raphe is filiform, straight to slightly undulate. The external proximal raphe ends are prominent and dilated. Areolae are punctate. Striae are decussate, that is, areolae are arranged in multiple rows - a transapical row and two oblique rows.

This is a distinctive species. Our observations expand the size range of this taxon beyond that reported by Patrick and Reimer (1966). Note that the valve apices are variable in shape and typically more rostrate than the population illustrated here (Edlund et al. 2006).

Original Description

Basionym: Navicula placenta
Author: Ehrenb. 1854
Length Range: µm
Striae in 10 µm:

Original Description

Original Images

Cite This Page:
Kociolek, P. (2011). Decussata placenta. In Diatoms of the United States. Retrieved May 20, 2018, from

Species: Decussata placenta

Contributor: Pat Kociolek

Reviewer: Mark Edlund


Edlund, M.B., Brant, L.A., Levkov, Z. and Nakov, T. (2006). An emended description of Decussata (Patrick) Lange-Bertalot & Metzeltin that includes protoplast organization and detailed valve and cingulum ultrastructure. Diatom Research 21: 269-280. 10.1080/0269249X.2006.9705669

Krammer, K. and Lange-Bertalot, H. (1986). Bacillariophyceae. 1. Teil: Naviculaceae. In: Ettl, H., J. Gerloff, H. Heynig and D. Mollenhauer (eds.) Süsswasserflora von Mitteleuropa, Band 2/1. Gustav Fisher Verlag, Jena. 876 pp.

Lange-Bertalot, H. (2000). Transfer to the generic rank of Decussata Patrick as a subgenus of Navicula Bory. Iconographia Diatomologica 9: 670-673.

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.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA

California Academy of Sciences (CAS)

Decussata placenta CAS

North American Diatom Ecological Database (NADED)

NADED ID: 219001

Autecology Discussion

Widely distributed, found commonly in aerophilous conditions

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

Decussata placenta

EMAP Response Plots

Decussata placenta

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.