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Diatoms of the United States is now known as Diatoms of North America.
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Williams and Round 1988      Category: Araphid
TYPE SPECIES: Fragilariforma virescens (Ralfs) Williams and Round




Image Credit: Eduardo Morales, Kerry Howard, Loren Bahls, Sarah Spaulding

CLASS: Fragilariophyceae
  ORDER: Fragilariales
    FAMILY: Fragilariaceae

  1. Central sternum very narrow, or absent
  2. Cells joined by spines to form colonies
  3. Striae uniseriate

The valve margins of Fragilariforma are variable and may be linear, lanceolate, or elliptical with rostrate to capitate apices. In girdle view, frustules are rectangular in shape. Fragilariforma valves are characterized by a very narrow, or absent, central sternum. Striae are composed of distinct, uniseriate areolae. Frustules form linear colonies, linked by small marginal spines into ribbon like (band-shaped) colonies. A single rimoportula is present at one pole and is aligned with a stria. Living cells contain multiple discoid plastids.

Some species of Fragilariforma grow in ephemeral habitats, subject to periodic drying. In such habitats, frustules often form internal valves. Several species are typical of boreal wetlands and others are endemic to subtropical regions.

Cite This Page:
Spaulding, S., and Edlund, M. (2008). Fragilariforma. In Diatoms of the United States. Retrieved May 27, 2018, from

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