Visit us at

Diatoms of the United States is now known as Diatoms of North America.
This site has been redesigned and updated, and will be closing soon.


Ehrenberg 1843      Category: Symmetrical biraphid
TYPE SPECIES: Pinnularia viridis (Nitzsch) Ehrenberg




Image Credit: Sarah Spaulding, Megan Otu

CLASS: Bacillariophyceae
  ORDER: Naviculales
    FAMILY: Pinnulariaceae

  1. Striae chambered, may form longitudinal lines
  2. External proximal raphe ends dilated, bent slightly
  3. Distal raphe ends deflected

Frustules of Pinnularia may be large, up to 300 µm in length. The striae are alveolate. Internally, the striae are positioned within chambers. The openings of the chambers are evident as longitudinal lines that cross the striae. The raphe system may be straight or complex. Externally, the proximal raphe ends are expanded and bent slightly to the same side. The distal raphe ends are deflected and may form a distinct, curving bend (a question mark shape). The central area may be expanded to one or both sides. Living cells contain two plastids.

Pinnularia is closely related to Caloneis and some authors suggest they should be considered as the same genus.

Pinnularia contains a large number of species and is often abundant in low conductance, slightly acid waters.

Cite This Page:
Spaulding, S., and Edlund, M. (2009). Pinnularia. In Diatoms of the United States. Retrieved May 25, 2018, from

Contributor: Sarah Spaulding | Mark Edlund - January 2009
Reviewer: Sam Rushforth - June 2010