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Brachysira microcephala

(Grunow) Compère 1986      Category: Symmetrical biraphid
BASIONYM: Navicula microcephala Grunow 1867

REPORTED AS: Anomoeoneis vitrea (Patrick and Reimer 1966, pg. 380, pl. 33, figs 12, 13) 

Brachysira hannae


Brachysira neoacuta

LM scalebar = 10 µm = 80 pixels.


Contributor: Paul Hamilton - December 2010
Length Range: 17-30 µm
Width Range: 3.5-7 µm
Striae in 10 µm: 30-36


Valves are lanceolate to rhombic-lanceolate with protracted, capitate apices. Some specimens are weakly asymmetric to the transapical axis, or heteropolar. Striae are radiate, except may be parallel at the apices. The central area is small, asymmetrically rounded and, in some specimens, undistinguishable from the axial area. The axial area is narrow and straight. The raphe is positioned within two ribs that lie on the external face of the valve The ribs terminate within the central area and at the apices. Raphe is straight, and filiform with undifferentiated proximal fissures and T-shaped distal fissures. Areolae are variable in shape, most are elongate rectangular openings, and are arranged to form the appearance of wavy hyaline areas. At the apices, each stria consists of a single elongated areola. In the SEM, small papillae (silica nodules) may be located on the external valve face between the striae. A rib is present along the valve margin and apex, separating the valve face from the mantle. Striae on the mantle are long uniseriate slits aligned with striae on the valve face. In SEM, a small helictoglossa is present. Internally, the areolae are covered by delineated hymenes.

Confusion regarding the taxonomy and nomenclature of B. microcephala, B. neoexilis and B. vitrea (sensu Patrick and Reimer, 1966) is examined by Patrick and Reimer (1966), Wolfe and Kling (2001) and Shayler and Siver (2004).

Note that the subcapitate to capitate form illustrated here more typical of this species. It is referred to as Morphotype 2 (Shayler and Siver 2004). Morphotype 1 is distinguished by apiculate rounded to weakly subcapitate apices. Morphotype 1 was found in habitats with a lower pH than habitats with Morphotype 2 (Siver et al., 2004). We consider these two morphotypes as separate entities and we suggest that further taxonomic clarification. According to Compère (1986; 1988) and Wolfe and Kling (2001), B. microcephala would encompass both morphotypes.

Second, the last paragraph of his description creates an impression that morphotype 1 in Shayler & Siver is a morphotype of B. microcephala, while in fact, it is a combination of B. brebissonii and B. arctoborealis.

Original Description

Basionym: Navicula microcephala
Author: Grunow 1867
Length Range: µm
Striae in 10 µm:

Original Description

N. microcephala Grun. - Achnanthidium microcephalum W. Smith Brit. Diat. t. 41 f. 380. (vix Kg.) - Navicula exillima Grunow in literis

Original Images

Cite This Page:
Hamilton, P. (2010). Brachysira microcephala. In Diatoms of the United States. Retrieved May 25, 2018, from

Species: Brachysira microcephala

Contributor: Paul Hamilton

Reviewer: Sarah Spaulding


Compère, P. (1986). Algues récoltées par J. Léonard dans le désert de Libye. Bulletin du Jardin Botanique National de Belgique 56(1/2):9-50.

Compère, P. (1988). Brachysira microcephala (Grunow) Compere nom correct de “Navicula exilis” Grunow 1860 non Kutzing 1844. Mem. Soc. Roy. Bot. Belg. 10: 9-11.

Grunow, A. (1867). Reise seiner Majestät Fregatte Novara um die Erde. Botanischer Theil. 1. Algen. Wein, aus der Kaiselich-Königlichen Hof-und Staasdruckerei, pp. 1-104., 11 pls.

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.

Shayler, H.A. and Siver, P.A. (2004). Biodiversity of the genus Brachysira in the Ocala National Forest, Florida, U.S.A. Proceedings of the Seventeenth International Diatom. Symposium Ottawa, Canada, 25th – 31st August 2002 (M. Poulin, ed.), Biopress limited, Bristol. p. 309-333.

Shayler, H.A. and Siver, P.A. (2004). Description of a new species of the diatom genus Brachysira (Bacillariophyta), Brachysira gravida sp. nov. from the Ocala National Forest, Florida, U.S.A. Nova Hedwigia 78: 399-409.

Siver, P.A. and Hamilton, P.B. (2011). Diatoms of North America: The Freshwater Flora of Waterbodies on the Atlantic Coastal Plain. Iconographia Diatomologica 22.

Wolfe, A.P. and Kling, H.J. (2001). A consideration of some North American soft-water Brachysira taxa and description of B. arctoborealis sp. nov. Lange-Bertalot-Festschrift Studies on Diatoms, Dedicated to Dr. Dr. h.c. Horst Lange-Bertalot on the occasion of his 65th birthday.

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Brachysira microcephala CAS

North American Diatom Ecological Database (NADED)

NADED ID: 18013

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

Brachysira microcephala

EMAP Response Plots

Brachysira microcephala

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.