Achnanthidium gracillimum

(Meister) Lange-Bertalot in Krammer and Lange-Bertalot 2004      Category: Monoraphid
BASIONYM: Microneis gracillima Meister 1912
SYNONYM(S): Achnanthes altergracillima Lange-Bertalot 

Achnanthidium exiguum


Achnanthidium kranzii

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova - August 2010
Length Range: 12-21 µm
Width Range: 3.0-3.7 µm
Striae in 10 µm: 21-25 in the center valve, 36-45 at the valve ends


Valves are linear-lanceolate with narrowly rostrate to subcapitate ends. The raphe valve is concave and the rapheless valve is convex. Both valves possess a linear axial area, which widens slightly in the middle portion of the valve. No central area is present. The striae are parallel or slightly radiate throughout both valves. The external openings of the areolae are transapically elongated, appearing as narrow slits. Each stria in the middle part of the valve is composed of 4-5 areolae. Short marginal striae are often present in the middle portion of both valves. The raphe is straight, filiform. The terminal raphe fissures are sharply bent. Externally, the central raphe ends are teardrop-shaped. Internally, the central raphe ends curve to opposite sides.

Original Description

Basionym: Microneis gracillima
Author: Meister 1912
Length Range: 25-40 µm
Width Range: 3-4 µm
Striae in 10 µm: 30

Original Description

Schalen linear-lanzettlich mit gerundeten, breiten Enden, 25-40 μ lang, 3-4 μ breit. Streifen parallel, etwa 30 in 10 μ; Unterschale mit kleinem Mittelfeld.

Original Images

Cite This Page:
Potapova, M. (2010). Achnanthidium gracillimum. In Diatoms of the United States. Retrieved May 24, 2017, from

Species: Achnanthidium gracillimum

Contributor: Marina Potapova

Reviewer: Sarah Spaulding


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.

Meister, F. (1912). Die Kieselalgen der Schweiz. Beiträge zur Kryptogamenflora der Schweiz, 4/1, 1–254.

Ponader, K. and Potapova, M. (2007). Diatoms from the genus Achnanthidium in flowing waters of the Appalachian Mountains (North America): Ecology, distribution and taxonomic notes. Limnologica - Ecology and Management of Inland Waters 37: 227-241 . 10.1016/j.limno.2007.01.004

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Achnanthidium gracillimum CAS

North American Diatom Ecological Database (NADED)


Autecology Discussion