Lyngbye 1819      Category: Araphid
TYPE SPECIES: Fragiliaria pectinalis (O. M├╝ller) Lyngbye




Image Credit: Eduardo Morales

CLASS: Fragilariophyceae
  ORDER: Fragilariales
    FAMILY: Fragilariaceae

  1. Frustules rectangular to lanceolate, in girdle view
  2. Frustules joined by spines to form colonies
  3. Single rimoportula present

Fragilaria frustules are rectangular to lanceolate in girdle view. The pattern of ornamentation on the valve face is variable, but a central sternum is generally present. Frustules are joined by small marginal spines to form ribbon like (band-shaped) colonies. A single rimoportula is present, usually positioned at a distal end. Small, apical porefields are also present. Living cells contain plastids composed of 2 plates, positioned against the valve face.

Fragilaria is often abundant in the plankton of lakes, including the species F. crotonensis, F. capucina, and F. vaucheria. Like Asterionella formosa, F. crotonensis is a species that is considered to have a world wide distribution and is also considered to be introduced by human activities.

A broad concept of Fragilaria is applied in Krammer and Lange-Bertalot (1991), while a much narrower concept is applied in Williams and Round (1987). Depending upon the school that a particular author follows, species may be considered within Fragilaria, Synedra, or a number of other genera. This website generally follows the work of Williams and Round (1987).

Cite This Page:
Spaulding, S., and Edlund, M. (2008). Fragilaria. In Diatoms of the United States. Retrieved October 09, 2015, from

Contributor: Sarah Spaulding | Mark Edlund - December 2008