Bukhtiyarova and Round 1996      Category: Monoraphid
TYPE SPECIES: Achnanthes pusilla Grunow in Cleve and Grunow




Image Credit: Marina Potapova

CLASS: Bacillariophyceae
  ORDER: Achnanthales
    FAMILY: Achnanthaceae

  1. Frustules heterovalvar - one valve with a raphe, the other lacking a raphe
  2. Raphe valve concave, rapheless valve convex
  3. Valves very small, linear-elliptic to lanceolate
  4. Striae uni- or biseriate
  5. Terminal raphe fissures absent

The valve outline is linear, elongate or lanceolate, with rounded apices. The striae are parallel throughout the valve, on both raphe and rapheless valves. The striae are variable and may be uni- or biseriate. The axial area is narrow. The raphe is straight with expanded proximal raphe ends. Terminal raphe fissures are absent. The central area on the raphe valve varies in both size and shape. Areolae are present on the valve mantle.

Rossithidium is similar to Achnanthidium and there is some question about the merits of a separate genus. Rossithidium was established to include three linear species of Achnanthidium (Round and Bukhtiyarova 1996) including Achnanthes linearis W. Smith. However, the separation of Rossithidium from Achnanthidium may need to be re-examined (Kingston 2003). Many ecological surveys do not discriminate the species in Achnanthidium and Rossithidium.

Cite This Page:
Potapova, M., Spaulding, S., and Edlund, M. (2008). Rossithidium. In Diatoms of the United States. Retrieved April 23, 2018, from

Contributor: Marina Potapova | Sarah Spaulding | Mark Edlund - December 2008