Platessa stewartii

(R.M.Patrick) Potapova 2004      Category: Monoraphid
BASIONYM: Achnanthes stewartii R.M.Patrick 1945
SYNONYM(S): Planothidium stewartii (R.M.Patrick) Lange-Bert. in Krammer and Lange-Bert. 

Platessa lutheri


Platessa strelnikovae

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova - December 2010
Length Range: 11-16 µm
Width Range: 5.7–7.0 µm
Striae in 10 µm: 14–18


Valves are elliptic. Both valves have a linear axial area. The central area on the raphe valve is transapically rectangular, often reaching the valve margin. The central area on the rapheless valve is small and often asymmetric. The striae are radiate and biseriate. The raphe is straight, filiform and lacks terminal fissures. Distal external raphe ends are slightly expanded and straight. Proximal external raphe ends are expanded and sharply turned to one side. Areolae are round. There is a row of areolae on the valve mantle, with one areola at the end of each stria.

Original Description

Basionym: Achnanthes stewartii
Author: R.M.Patrick 1945
Length Range: 16 µm
Width Range: 7.5 µm
Striae in 10 µm: 14

Original Description

Valvae ellipticae, 16 μ longae, 7.5 μ latae, area axiali angusta, costis tenuibus 14 in 10 μ, serie duplici punctorum parvorum interpositu

Original Images

Cite This Page:
Potapova, M. (2010). Platessa stewartii. In Diatoms of the United States. Retrieved April 20, 2018, from

Species: Platessa stewartii

Contributor: Marina Potapova

Reviewer: Sarah Spaulding


Krammer, K. and Lange-Bertalot, H. (2004). Bacillariophyceae 4. Teil: Achnanthaceae, Kritische Erganzungen zu Navicula (Lineolatae), Gomphonema Gesamtliteraturverzeichnis Teil 1-4 [second revised edition]. In: H. Ettl et al., Suesswasserflora von Mitteleuropa. Spektrum Akademischer Verlad Heidelberg, 468 pp.

Patrick, R.M. (1945). A taxonomic and ecological study of some diatoms from the Pocono Plateau and adjacent regions. Farlowia 2(2):143-221.

Potapova, M. (2012). New species and combinations in monoraphid diatoms (Family Achnanthidiaceae) from North America. Diatom Research 27(1): 29-42. doi:10.1080/0269249X.2011.644636

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Platessa stewartii CAS

North American Diatom Ecological Database (NADED)

NADED ID: 155035

Autecology Discussion

Platessa stewartii was shown to have preference for a low calcium content, while its conductivity optimum (based on a dataset of 2674 river samples from the USA) was 134 μm/cm (Potapova & Charles 2003).

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

Platessa stewartii

EMAP Response Plots

Platessa stewartii

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.