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Interstria: Interstria was a term proposed to describe the silica between striae (Ross et al. 1979), but it has been replaced by virga (Cox 2011, Cox 2012).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.

Citations

Cox, E.J. (2011) Morphology, cell wall, cytology, ultrastructure, and morphogenetic studies. Overview and specific observations. In: The Diatom World (J. Seckbach and J.P. Kociolek, Eds,), Cellular origin, life in extreme habitats and astrobiology, Vol. 19, pp. 21–45, Springer, Dordrecht.
Cox, E.J. (2012) Ontogeny, homology, and terminology - wall morphogenesis as an aid to character recognition and character state definition for pennate diatom systematics Journal of Phycology 48: 1–31

Publication Link: 10.1111/j.1529-8817.2011.01081.x
Cox, E.J. and Ross, R. (1981) The striae of pennate diatoms. In: R. Ross, ed., Proceedings of the Sixth Symposium on Fossil and Recent Diatoms. O. Koeltz, Koenigstein. pp. 267–278.
Round, F.E., Crawford, R.M. and Mann, D.G. (1990) The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.

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.