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Diatoms of the United States is now known as Diatoms of North America.
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Kützing 1844      Category: Symmetrical biraphid
TYPE SPECIES: Diadesmis confervacea Kützing




Image Credit: Eugene Stoermer

CLASS: Bacillariophyceae
  ORDER: Naviculales
    FAMILY: Diadesmidaceae

  1. Areolae elongate
  2. Frustules small, usually less than 20 µm in length
  3. Cells form band-like colonies

Diadesmis is biraphid, although the raphe often becomes secondarily filled with silica. Frustules of Diadesmis are small, usually less than 30 µm in length. The striae are composed of areolae elongated in the transapical direction, a characteristic that may be difficult to discern in the LM. Frustules form band-like colonies, which may be linked by marginal spines. The raphe systems of many frustules are secondarily filled with silica, and a raphe may not be evident in valve view. In girdle view, however, a central nodule and helictoglossa may be seen - evidence of the presence of a raphe.

Diadesmis is considered an aerophilic taxon. It grows on mosses and on damp rocks, often in low conductivity, slightly acid waters. With the description of the new genus Humidophila, Diadesmis now includes D. confervacea and varieties.

Cite This Page:
Spaulding, S., and Edlund, M. (2008). Diadesmis. In Diatoms of the United States. Retrieved May 22, 2018, from

Contributor: Sarah Spaulding | Mark Edlund - December 2008
Reviewer: Sam Rushforth - May 2010


March 27th, 2015 - Change in genus concept

In 2014, Lowe et al. published a new genus, Humidophila to include a large number of species that had been included in the genus Diadesmis. The page for Diadesmis has been edited to reflect the new, narrower concept of the type of D. confervacea. - S. Spaulding