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Didymosphenia (Gomphonemataceae)

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Diagnostic features

Valves identical, both possessing a raphe (i.e. the genus is biraphid).  Large cells shaped like an Egyptian sarcophagus in valve view, with large brown chloroplast (often having a "fold" at one edge). Wedge shaped in girdle view. A cluster of 3 pores occurs on the valve face near the central raphe ends (although these may be difficult to see).  Often attached to the bed by long mucilaginous stalks, which may be more abundant than the cells themselves. Forms thick blooms commonly referred to as "didymo" or "rock snot".

[Didymosphenia] bloom, Hawea River. Photo: Manaaki Whenua Image
Didymosphenia bloom, Hawea River. Photo: Manaaki Whenua
[Didymosphenia] on mucilaginous stalks, X200. Photo: Manaaki Whenua Image
Didymosphenia on mucilaginous stalks, X200. Photo: Manaaki Whenua

Typical habitats

Stony bottom streams and rivers with good water quality

Classification

Kingdom Chromista
Phylum Ochrophyta
Class Bacillariophyceae
Order Cymbellales
Family Gomphonemataceae
Common name Diatoms