Ulnaria contracta

(Østrup) E.Morales and M.L.Vis 2007      Category: Araphid
BASIONYM: Synedra ulna var. contracta Østrup 1901
SYNONYM(S): Synedra ulna var. oxyrhynchus f. contracta Hust. 1930 | Fragilaria ulna var. contracta (Østrup) Main 1988 

Tryblionella hungarica


LM scalebar = 10 µm = 40 pixels.


Contributor: Ian Bishop - November 2015
Length Range: 65-149 µm
Width Range: 6.5-6.8 µm
Striae in 10 µm: 10-12


Valves are elongate and linear, with a variably constricted central margin. In larger specimens, the central margins are slightly constricted to nearly straight. The valve tapers slightly in the middle 3/4 of the valve, and narrows to approximately 1/3 the maximum width near the valve ends. Valves are 6.5 to 6.8 µm in width at the center, and away from the central area are 6.4 to 8.1 µm in width. Apices are rostrate to sub-capitate, and rounded to truncated. Striae are nearly parallel and arranged opposite one another; however, near the poles the striae begin to curve and become alternate to one another. The axial area is narrow and linear, expanding slightly near the central area. The central area is rectangular and contains ghost striae throughout. The central area may be surrounded by shortened, marginal striae. Individual areolae not discernible in LM. Each valve has two rimoportula, one at each apex.

Note that the specimens presented here differ from the original type illustration (below). The type material should be examined to resolve the circumscription of this taxon.

Original Description

Basionym: Synedra ulna var. contracta
Author: Østrup 1901
Length Range: 112 µm
Width Range: 7.5 at widest, 6 in the middle µm
Striae in 10 µm: 9

Original Description

Var. contracta m. Fig. 660/1. L. 0,112 mm., Br., greatest, 0,075 mm., in the middle 0,06 mm. Striae 9 in 0,01 mm. Slightly constricted. Striae absent from the centre. This variety must doubtless be regarded as a transitional form of Synedra Goulardii Bréb. in litt. (Cl. & Grun. arc. Diat. tab. VI, fig. 119), which is, however, shorter and broader. S. Goulardii has been found in Buenos Ayres, Porto Rico, Kamchatka and near Jenisei. Found in a gathering from the Faeroes labelled: >Green Algae from a swamp on Nolso<.

NOTE: the above reported width range was changed to correct an original publication error. Østrup reported original widths as 75 μm and 60 μm.

Original Images

Cite This Page:
Bishop, I. (2015). Ulnaria contracta. In Diatoms of the United States. Retrieved April 22, 2018, from http://westerndiatoms.colorado.edu/taxa/species/synedra_ulna_var._contracta

Species: Ulnaria contracta

Contributor: Ian Bishop

Reviewer: Eduardo A. Morales


Compère, P. (2001). Ulnaria (Kützing) Compère, a new genus name for Fragilaria subgen. Alterasynedra Lange-Bertalot with comments on the typification of Synedra Ehrenberg. In: Jahn, R., Kociolek, J.P., Witkowski, A. and Compère, P. (eds), Lange-Bertalot-Festschrift: Studies on Diatoms. Dedicated to Prof. Dr. Dr. h.c. Horst Lange-Bertalot on the occassion of his 65th Birthday. A.R.G. Gantner Verlag. K.G. pp. 97-102.

Hustedt, F. (1930). Bacillariophyta (Diatomeae). In: Die Subwasser Flora Mitteleuropas. (A. Pascher, ed.),10, Gustav Fischer, Jena. 468 pp.

Morales, E.A. and Vis, M.L. (2007). Epilithic diatoms (Bacillariophyceae) from cloud forest and alpine streams in Bolivia, South America. Proceedings of the Academy of Natural Sciences of Philadelphia 156: 123-155.

Østrup, E. (1901). Freshwater-Diatoms from the Faeröes. Botany of the Faeroes, part 1. Det. Nordiske Forlag. Copenhagen. pp. 260-290.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA

California Academy of Sciences (CAS)

Ulnaria contracta CAS

North American Diatom Ecological Database (NADED)


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

Ulnaria contracta

EMAP Response Plots

Ulnaria contracta

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.