Achnanthidium exiguum
(Grunow) Czarnecki 1994 Category: Monoraphid
BASIONYM: Achnanthes exigua Grunow in Cleve & Grunow 1880
REPORTED AS: Achnanthes exigua var. heterovalvata (Krasske 1923) | Achnanthidium exiguum var. heterovalvum ( (Krasske) Czarnecki 1994)
LM scalebar = 10 µm = 80 pixels.
Observations
Contributor: Marina Potapova - December 2010
Length Range: 5-17 µm
Width Range: 4.5-6.2 µm
Striae in 10 µm: 24-34 in center of raphe valve, 20-25 in center of rapheless valve, up to 45 at apices
Description
Valves are linear-elliptical to elliptical-lanceolate with narrowly capitate, subcapitate, rostrate, or subrostrate apices, 4.5-6.2 µm wide, 5-17 µm long. Larger valves are sometimes slightly constricted in the middle. Both raphe and rapheless valves have a narrow slightly sigmoid axial area. The raphe valve has a stauros that is often slightly wider on one side. The rapheless valve has a small, transapically rectangular, often asymmetrical, central area. The raphe is straight, but deflected to opposite sides near the apices with terminal raphe fissures strongly curved to opposite sides. The central external raphe ends are simple, located in slight “pin-hole” depressions, giving the appearance that they are expanded. Internally, the central raphe ends curve toward opposite sides. The striae are radiate on both valves, but almost parallel at the apices. Raphe valve has 24-34 striae in 10 µm in mid-valve, up to 40-45 in 10 µm at the apices; raphless valve has 20-25 striae in 10 µm in mid-valve, up to 35-40 in 10 µm at apices. A few very small areolae may be present on the mantle of both valves. Areolae are round or transapically elongated externally, apically elongated internally, ca. 55-70 in 10 µm within the striae.
The variety Achnanthes exiguum var. heterovalvata was described as having a striae density of 34 in 10 µm. Our observations of material from the US, however, show that the nominate variety includes a gradient of stria density from 24 to 34 in 10 µm. We see that the variation of A. exiguum is quite broad, and therefore, consider Achanthes exiguum var. heterovalvata as a subjective synonym.
Original Description
Basionym: Achnanthes exigua
Author: Grunow in Cleve & Grunow 1880
Length Range: 11.3 µm
Striae in 10 µm:
Original Description
St. minutissima, elliptico-lanceolata, breviter rostellata, Long. 1/200´´´
Original Images
Cite This Page:
Potapova, M. (2010). Achnanthidium exiguum. In Diatoms of the United States. Retrieved May 20, 2013, from http://westerndiatoms.colorado.edu/taxa/species/achnanthidium_exiguum
Species: Achnanthidium exiguum
Contributor: Marina Potapova
Reviewer: Sarah Spaulding
Image Credit: Marina Potapova
- Valves with capitate to subrostrate apices
- Raphe valve with stauros
- Rapheless valve with small transversely rectangular central area
- Striae more dense on raphe valve than on rapheless valve
- Terminal raphe ends curved to opposite sides
Valves are linear-elliptical to elliptical-lanceolate with narrowly capitate to subrostrate apices, 4.5-6.2 µm wide, 5-17 µm long. The raphe valve has a stauros. The rapheless valve has a small, transapically rectangular central area. The raphe is straight, but deflected to opposite sides near the apices with terminal raphe fissures strongly curved to opposite sides. The central external raphe ends appear to be expanded. The striae are radiate on both valves, but almost parallel at the apices. Raphe valve has 24-34 striae in 10 µm in mid-valve, up to 40-45 in 10 µm at apices; rapheless valve has 20-25 striae in 10 µm in mid-valve, up to 35-40 in 10 µm at apices.
Compare
Achnanthidium exiguum is easily distinguished from other monoraphid diatoms by the linear-elliptical valves with narrowly capitate to subrostrate apices and by the presence of stauros on the raphe valve. Achnanthidium exiguum var. constrictum differs from the nominate variety only by strongly constricted valve margins. Smaller specimens of A. exiguum are sometimes incorrectly identified as Achnanthes exigua var. elliptica, because of their elliptical-lanceolate shape. Larger specimens of Achnanthes exigua var. elliptica, however, are needed to distinguish this variety from the nominate variety.
Achnanthidium exiguum var. constrictum
(Grunow) Andresen, Stoermer & Kreis
Achnanthes exigua var. elliptica
Hustedt
Citations
Cleve, P.T. and Grunow, A. (1880). Beiträge zur Kenntniss der Arctischen Diatomeen. Kongliga Svenska-Vetenskaps Akademiens Handlingar, Vol: 17, Issue: 2, 121 pp., 7 pls.
Czarnecki, D.B. (1994). The Freshwater Diatom Culture Collection at Loras College, Dubuque, Iowa. Kociolek, J.P. (ed.) Proceedings of the 11th International Diatom Symposium, California Academy of Sciences, San Francisco, CA, p. 155-173.
Links & ID's
Index Nominum Algarum (INA)
California Academy of Sciences (CAS)
North American Diatom Ecological Database (NADED)
NADED ID: 1024
Autecology Discussion
EMAP Assessment
Sampling for 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). Streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming). Over 1200 sites on 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
Achnanthidium exiguum
Distribution
The distribution map represents the relative abundance of this Achnanthidium exiguum in the western EMAP study. Relative abundance is a measure of the proportion of cells of this species based on a "fixed count" of 300 total diatom cells counted and identified. Each of the western EMAP sample sites is shown, either with a black dot for sites where Achnanthidium exiguum was not recorded, or with a red circle indicating the relative abundance of Achnanthidium exiguum.
Note that the size of the proportional symbols varies between species to help show both abundant and rare species.
Scale for the map to the left
EMAP Response Plots
Achnanthidium exiguum
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.