Virga

A virga is the solid silica band between two striae. The plural is virgae.

The Latin words virga and vimen were chosen for these terms because the structure of many pennate diatoms with striae bears some resemblance to a woven basket. A virga (rod) is the stiffer material used for the ribs of the basket and a vimen (pliant twig) is the flexible material woven between the ribs (Cox and Ross 1981 p. 272).

During the morphogenesis of many pennate diatoms with striae, virgae and vimines join to create the network of gaps which become the areolae.

See also costa and vimen.

Alternative Terms

Interstria

Interstria was a term proposed to describe the silica between striae (Ross et al. 1979), but it has been replaced by virga (Cox 2011, Cox 2012). Virga is considered to better describe the structure and morphogenesis of this valve feature.

Virga
Image Credit: Figure adapted from Round et al. (1990).
Diagram of a valve in the early stages of silica deposition. A single virga is indicated by the arrow. Virgae are the solid silica bands between the striae.