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Achnanthidium pyrenaicum

(Hust.) H.Kobayasi 1997      Category: Monoraphid
BASIONYM: Achnanthes pyrenaica Hust. 1966

Achnanthidium minutissimum


Achnanthidium reimeri

LM scalebar = 10 µm = 80 pixels.


Contributor: Marina Potapova - May 2009
Length Range: 10-16 µm
Width Range: 2.5-4.0 µm
Striae in 10 µm: 20-25 in the center, 34-40 at the raphe valve ends; 20-28 in the center, 32-38 at the rapheless valve ends


Valves are linear-lanceolate with slightly drawn-out ends, often slightly asymmetrical about median transapical plane. Valves are 10-16 µm in length, and 2.5-4.0 µm wide. The raphe valve is concave. The raphe valve has a linear axial area, which widens slightly in the middle portion of the valve. This rectangular central area that reaches valve margin is often asymmetrical and may be termed a facia, or subfascia. Externally, the terminal raphe fissures are hooked towards the same side of the valve. Externally, the central raphe ends are teardrop-shaped and internally, curved to opposite sides. The rapheless valve is convex, with a narrow linear axial area widening slightly in the middle. The striae are parallel throughout both valves or very slightly radiate in the middle of the valve and slightly convergent at the apices. On the raphe valve, the striae density is 20-25 in 10 µm in the center and 34-40 in 10 µm at the apices. On the rapheless valve, the striae density is 20-28 in 10 µm in the center and 32-38 in 10 µm at the apices. External openings of areolae are transapically elongated or circular. Each stria in the center of the valve contains 2-4 areolae. The valve mantle bears one row of areolae.

Original Description

Basionym: Achnanthes pyrenaica
Author: Hust. 1966
Length Range: 7–20 µm
Width Range: 3–4 µm
Striae in 10 µm: 25 in the center of raphe valve, 21 in the center of the rapheless valve

Original Description

Schalen linear-lanzettlich mit stumpf gerundeten, oft leicht vorgezogen bis schwach kopfigen Enden, 7-10 µm lang, 3-4 µm breit, die kleinsten Individuen sind oft völlig elliptisch. Raphenlose Schalen mit sehr enger Pseudoraphe, Transapikalstreifen etwa 21 in 10 µm, senkrecht zur Mittellinie, nur an den äubersten Enden leicht radial, die Mittelstreifen jederseits der Pseudoraphe gewöhnlich etwas verkürtz. Raphenschale mit fadenförmiger raphe, Axialarea sehr eng, Zentralarea infolge der auch auf dieser Schale erfolgten Verkürzung der Mittelstreifen etwas quer verbreitert; Transapikalstreifen enger als auf der raphenlosen Schale, etwa 25 in 10 µm, durchweg leicht radial.

Original Images

Original text and images reproduced with permission by Teubner Verlag/GWV Fachverlage GmbH.

Cite This Page:
Potapova, M. (2009). Achnanthidium pyrenaicum. In Diatoms of the United States. Retrieved May 22, 2018, from

Species: Achnanthidium pyrenaicum

Contributor: Marina Potapova

Reviewer: Sarah Spaulding


Hustedt, F. (1939). Diatomeen aus der Pyrenaen. Berichte der Deutschen Botanischen Gesellschaft 56: 543-572.

Jüttner, I., Chimonides, J. and Cox, E.J. (2011). Morphology, ecology and biogeography of diatom species related to Achnanthidium pyrenaicum (Hustedt) Kobayasi (Bacillariophyceae) in streams of the Indian and Nepalese Himalaya. Algological Studies 136-137. 10.1127/1864-1318/2011/0136-0045

Kobayasi, H. (1997). Comparative studies among four linear-lanceolate Achnanthidium species (Bacillariophyceae) with curved terminal raphe endings. Nova Hedwigia 65: 147-163.

Potapova, M. (2006). Achnanthidium zhakovschikovii sp. nov. (Bacillariophyta) and related species from rivers of Northwestern Russia. Nova Hedwigia 82: 399-408. 10.1127/0029-5035/2006/0082-0399

Potapova, M. and Ponader, K.C. (2004). Two common North American diatoms, Achnanthidium rivulare sp. nov. and A. deflexum (Reimer) Kingston: morphology, ecology and comparison with related species. Diatom Research 19(1): 33-57.

Links & ID's

Index Nominum Algarum (INA)

Transfer INA
Original INA

California Academy of Sciences (CAS)

Achnanthidium pyrenaicum CAS

NCBI Genbank Taxonomy

Achnanthidium pyrenaicum NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 1023

Autecology Discussion

Although formation of mucilaginous stalks was never observed in A. pyrenaicum, this species might be able to produce stalks as other Achnanthidium species.