Psammothidium didymum

(Hust.) Bukht. and Round 1996      Category: Monoraphid
BASIONYM: Achnanthes didyma Hust. 1933

Psammothidium daonense


Psammothidium harveyi

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova - August 2010
Length Range: 6-9 µm
Width Range: 3.3-4.2 µm
Striae in 10 µm: 28-32 on raphe valve, 25-28 on rapheless valve


Valves are linear-elliptical, slightly constricted in the middle. The raphe valve has a linear axial area, which widens into a small circular or elliptical central area. The raphe is straight and lacks terminal fissures. Externally, the central and terminal raphe ends are very slightly expanded externally. Internally, the central raphe ends curve toward opposite sides internally. The rapheless valve has a large rhomboid axial area. The central area is usually not differentiated from the axial area on rapheless valve. Striae are radiate on both valves and interrupted at the valve margin. Striae number 28-32 in 10 µm on raphe valve and 25-28 in 10 µm on rapheless valve . One row of areolae is present on the mantle of both valves. The external openings of the areolae are square or rectangular.

Original Description

Basionym: Achnanthes didyma
Author: Hust. 1933
Length Range: 6-8 µm
Width Range: 3.5-4 µm
Striae in 10 µm: 30-34

Original Description

Schalen linear-elliptisch mit parallelen bis schwach konkaven Seiten und breit gerundeten Enden, 6-8 μ lang, 3.5-4 μ breit. Raphenlose Schalen mit breit linearer Pseudoraphe, Transapikalstreifen kurz, sehr wenig radial, 26-28 in 10 μ. Raphenschale mit feiner, fadenförmiger Raphe mit einander genäherten Zentralporen, Axialarea sehr eng, um den Mittelknoten kaum erweitert; Transapikalstreifen 30-34 in 10 μ, in der Mitte kräftiger als vor den Polen, senkrecht zur Mittellinie oder nur wenig radial, besonders vor den Polen.

Original Images

Cite This Page:
Potapova, M. (2010). Psammothidium didymum. In Diatoms of the United States. Retrieved April 23, 2018, from

Species: Psammothidium didymum

Contributor: Marina Potapova

Reviewer: Sarah Spaulding


Bukhtiyarova, L. and Round, F. E. (1996). Revision of the genus Achnanthes sensu lato. Psammothidium, a new genus based on Achnanthidium marginulatum. Diatom Research 11: 1-30. 10.1080/0269249X.1996.9705361

Hustedt, F. (1933). Die Kieselalgen Deutschlands, Österreichs und der Schweiz unter Berücksichtigung der übrigen Länder Europas sowie der angrenzenden Meeresgebiete. In: L. Rabenhorst (ed.), Kryptogamen Flora von Deutschland, Österreich und der Schweiz. Akademische Verlagsgesellschaft m.b.h. Leipzig, Vol. 7, Part 2, pp. 321-432.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA
Original INA

California Academy of Sciences (CAS)

Psammothidium didymum CAS

North American Diatom Ecological Database (NADED)

NADED ID: 186012

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

Psammothidium didymum

EMAP Response Plots

Psammothidium didymum

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.