Contributor: Loren Bahls - April 2016
Length Range: 15-20 µm
Width Range: 6.4-7.2 µm
Striae in 10 µm: 30-32 near the center of the raphe valve, 24-28 near the center of the rapheless valve
Valves are linear-elliptic with narrow subcapitate apices. The raphe valve has a very narrow axial area that widens abruptly into a transverse fascia. The fascia is shaped like a bow tie and sometimes bordered by a few shortened striae. On the rapheless valve, the axial area is wider and expands gradually to merge with an asymmetric, irregular transverse central area. The raphe is straight. The terminal fissures appear to curve in opposite directions. The proximal raphe ends are expanded in the shape of tear drops. Striae on the rapheless valve are nearly parallel at the valve center but otherwise radiate, more so near the apices. Striae on the rapheless valve are also more closely spaced near the apices. Striae on the raphe valve are strongly radiate throughout and a bit more closely spaced near the apices.
Cleve-Euler (1953) amended her original description to confirm the presence of a fascia and to give more a accurate stria count: 24 in 10 µm on the rapheless valve and about 30 in 10 µm on the raphe valve. In LM, this taxon is morphologically similar to Achnanthidium exiguum and should probably be transferred to Achnanthidium.
Basionym: Achnanthes rostellata
Author: Cleve-Euler 1934
Length Range: 17 µm
Width Range: 6-6.5 µm
Striae in 10 µm: 21-22 on the raphe valve, about 19 on the rapheless valve
Cleve-Euler, A. (1934). The diatoms of Finnish Lapland. Societas Scientiarum Fennica. Commentationes Biologicae. 4(14):154 pp.
Cleve-Euler, A. (1953). Die Diatomeen von Schweden und Finnland. Teil III. Monoraphideae, Biraphideae 1. Authorized Reprint 1968, Bibliotheca Phycologica, Band 5, J. Cramer, Lehre.
Foged, N. (1974). Freshwater Diatoms in Iceland. Bibliotheca Phycologica, Band 15, J. Cramer, Vaduz, 118 pp. + 36 plates.
Krammer, K. and Lange-Bertalot, H. (2004). Bacillariophyceae 4. Teil: Achnanthaceae, Kritische Erganzungen zu Navicula (Lineolatae), Gomphonema Gesamtliteraturverzeichnis Teil 1-4 [second revised edition]. In: H. Ettl et al., Suesswasserflora von Mitteleuropa. Spektrum Akademischer Verlad Heidelberg, 468 pp.
Krasske, G. (1937). Diatomeen aus den postglazialen Seen auf Rügen. Arch. Hydrobiol. 31: 38-53.
Lange-Bertalot, H., Kulbs, K., Lauser, T., Norpel-Schempp, M. and Willmann, M. (1996). Diatom Taxa introduced by Georg Krasske: Documentation and Revision. Iconographia Diatomologica (H. Lange-Bertalot, ed.), Vol. 3, Koeltz Scientific Books, Konigstein, 358 pp.
This is a northern species found in cold, oligotrophic waters. It was described from Finnish Lapland (Cleve-Euler 1934) and later reported from Iceland (Foged 1974). The specimens illustrated here were collected from four small lakes in the Rocky Mountains of Montana, near the Canadian border. Three of these lakes are in Glacier National Park. In these four lakes electrical conductance ranges from 30 to 250 µS/cm and pH ranges from 7.2 to 7.8.
Johns Lake, Glacier National Park, Montana: home of A. rostellata