SEM-Photographs of Bacillariophyceae

Bayerisches Landesamt für Wasserwirtschaft

The diatoms (Bacillariophyceae) with their approximately 16,000 genera represent the richest group among the algae. They exist as individuals or in colonies, with every diatom consisting of one single cell surrounded by a rigid cellular wall. Unique in the entire realm of plants, the diatoms have a cellular wall, where silicate is embedded in a way that it forms each type of typical structures of amazing beauty. The two valves of the cellular wall form a box, where the edges of the top surpass the edges of the bottom. Diatoms can be found almost everywhere; there is hardly a biotope, humid permanently or at least periodically, which is not occupied by them. As the base of the food chain, they are playing an important ecological part.

Diatoms exist since the Jurassic-Age, which means since approximately 190 millions of years. Their shells have built whole geological formations called diatomite.

After Simonsen (1979) the diatoms are divided in two orders:

1. Structural center normally formed by a point, auxospore formation by oogamy: Centrales
2. Structural center normally formed by a line, auxospore formation not by oogamy: Pennales

Literature: Simonsen, R. (1979). the Diatom System: Ideas on Phylogeny. Bacillaria 2: 9–71. J.Cramer, Braunschweig.

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