Polar bar

In diatoms, the pigmented organelle that is the site of photosynthesis.

Plastids contain carotinoid pigments such as beta-carotene, diatoxanthin, diadinoxanthin, and fucoxanthin. They also contain a combination of chlorophylls a, c1, c2, and c3, depending on the species.

Most diatom plastids appear golden brown because the carotenoid pigments mask the color of the chlorophylls.

Alternative Term


An older term, often used more in European literature.


A plastid can be defined as any organelle that is the site of manufacture and storage of important chemical compounds used by the cell. It may or may not contain pigments. A chloroplast is an example of a pigmented plastid, but the term, plastid, is preferred over chloroplast when referring to this organelle in diatoms.


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.

Smith, W. (1856). Synopsis of British Diatomaceae. John Van Voorst, London 1856. 2: 107pp., pls. 32-60, 61-62, A-E.