Planothidium biporomum

(M.H.Hohn and Hellerman) Lange-Bert. 1999      Category: Monoraphid
BASIONYM: Achnanthes biporoma M.H.Hohn and Hellerman 1963

Planothidium apiculatum


Planothidium delicatulum

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova - December 2010
Length Range: 12-25 µm
Width Range: 5.4-7.0 µm
Striae in 10 µm: 12-15


Valves are lanceolate with capitate to subrostrate apices. Raphe valve has a linear axial area and a variable central area - from transversely rectangular to elliptical. Rapheless valve has a linear-lanceolate axial area and an asymmetrical central area containing a hood on the internal valve surface. The raphe is straight with expanded external proximal endings. Terminal raphe fissures are curved to the secondary side of the valve. The striae are multiseriate, radiate throughout both valves.

Note that in the type population larger valves have only capitate apices. Populations from other locations have large valves (large valves are early stages in the vegetative life cycle) with subrostrate valve apices. These two morphologies are included here in the concept of Planothidium biporomum, but further studies may show that they represent separate species.

Original Description

Basionym: Achnanthes biporoma
Author: M.H.Hohn and Hellerman 1963
Length Range: 20-8-22.8 µm
Width Range: 6.8-7.0 µm
Striae in 10 µm: 14-16

Original Description

Valve lanceolate, ends subcapitate; length 20.8-22.8 μ, width 6.8-7.0 μ; striae straight, finely punctate, radiate throughout 14-16/10 μ; raphe valve: axial area narrow linear-lanceolate, central area moderate, transapically rectangular; raphe thin, sigmoid at terminal pores; rapheless valve: pseudoraphe narrowly linear lanceolate; unilateral horse-shoeshaped silaceous thickening superimposed on broad semicircular thickening. This taxon resembles several varieties of Achnanthes lanceolata (Bréb.) Grun. (K. sv. Vet-Akad. Handl. 17(2): 23, 1880) particularly A. lanceolata var. haynaldi (Saarsch.) Cl. (Diatomiste 2(17): 99, pl. 7, fig. 14, 1894). It differs in that the axial area of the raphe valve is distinctly lanceolate rather than linear and the terminal raphe pores are sigmoid, whereas in A. lanceolata var. haynaldii they are unilaterally bent. The rapheless valve differs from that of A. lanceolata var. haynaldii in that the pseudoraphe is lanceolate and the unilateral siliceous platform is composed of two overlapping areas of different thickness rather than a single platform.

Original Images

Cite This Page:
Potapova, M. (2010). Planothidium biporomum. In Diatoms of the United States. Retrieved April 21, 2018, from

Species: Planothidium biporomum

Contributor: Marina Potapova

Reviewer: Sarah Spaulding


Hohn, M.H. and Hellerman, J. (1963). The taxonomy and structure of diatom populations from three Eastern North American rivers using three sampling methods. Transactions of the American Microscopical Society 82(3):250-329.

Lange-Bertalot, H. (1999). Neue Kombinationen von taxa aus Achnanthes Bory (sensu lato). Iconographia Diatomologica 6: 276-289.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Planothidium biporomum CAS

North American Diatom Ecological Database (NADED)

NADED ID: 155006

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

Planothidium biporomum

EMAP Response Plots

Planothidium biporomum

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.