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Ulnaria (Fragilariaceae)

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Diagnostic features

Pennate diatom, elongate to needle-like in valve view, narrow rectangular in girdle view, valves identical, neither possessing a raphe (genus is araphid).  Striae in parallel rows, separated along the central axis of the cell at a thickened sternum. Central area lacking striae (or with very faint striae) in the centre of the valve.  Similar to Fragilaria but not forming ribbons of cells joined side to side.  Cells are often attached to a surface by one end.  Chloroplasts golden brown.

[Ulnaria], X320. Photo: Otago Regional Council & Manaaki Whenua Image
Ulnaria, X320. Photo: Otago Regional Council & Manaaki Whenua
[Ulnaria] on [Vaucheria], Taieri River, X160. Photo: Otago Regional Council & Manaaki Whenua Image
Ulnaria on Vaucheria, Taieri River, X160. Photo: Otago Regional Council & Manaaki Whenua

Typical habitats

Common in moderate to good quality streams, sometimes in lake plankton.

Classification

Kingdom Chromista
Phylum Ochrophyta
Class Bacillariophyceae
Order Fragilariales
Family Fragilariaceae
Common name Diatoms