Bory 1927      Category: Monoraphid
TYPE SPECIES: Achnanthes adnata Bory




Image Credit: Mark Edlund

CLASS: Bacillariophyceae
  ORDER: Achnanthales
    FAMILY: Achnanthaceae

  1. Frustules heterovalvar - one valve with a raphe, the other lacking a raphe
  2. Raphe valve usually possesses a fascia or stauros
  3. Valves shallow and arched in girdle view
  4. Rapheless valve without fascia, narrower sternum usually off center

The frustules of Achnanthes are heterovalvar. The raphe valve usually possesses a central area of thickened silica, called a fascia or stauros. The rapheless valve has no such central area and the sternum may be positioned near the valve margin. In girdle view, the mantle of the rapheless valve appears to be more ornamented than that of the raphe valve. The striae are uni-, bi-, or triseriate and composed of areolae covered by complex cribra, or sieve plates.

Cells may grow alone, or may form short chains. Living cells are usually attached to substrata by a mucilage stalk extending through one end of the raphe valve. Most species are found in marine habitats, but a few taxa occur inland including Achnanthes coarctata. Inland species are commonly associated with mosses and lichens in aerophillic habitats. Many common species previously classified in this genus are now recognized as species of Achnanthidium, Psammothidium, Planothidium, and other genera.

Cite This Page:
Spaulding, S., and Edlund, M. (2008). Achnanthes. In Diatoms of the United States. Retrieved April 19, 2018, from

Contributor: Sarah Spaulding | Mark Edlund - July 2008
Reviewer: Sam Rushforth - April 2010