Guide to Ulnaria

Valves are linear and elongate, with some species near 50 µm in length, others reaching greater than 500 µm in length. A narrow central sternum is present, with striae that meet from each side of the valve or are slightly offset. A central area may be present, varying from small and oval to rectangular and extending to the valve margins. The central area may contain "ghost striae", or faint striae that are present over part, or all, of the central area. One to two rimoportulae are present, at one or both apices. In many species, the apices are distinctly rostrate. Striae are punctate and may be uniseriate or biseriate. Girdle bands are closed.

Living cells are common in rivers and lakes. They are attached to the substrate by a mucilage pad secreted by an apical porefield.

The taxonomic history of Fragilaria leading to the establishment of Ulnaria is convoluted (Morales 2003, Silva and Hasle 2006, Williams 2011).

The genus Ulnaria was proposed to include species within the species complex surrounding Fragilaria ulna, that is, Fragilaria subgenus Alterasynedra Krammer and Lange-Bertalot 1991. It includes Ulnaria biceps (Kützing) Compère, U. capitata (Ehrenberg) Compère, U. lanceolata (Kützing) Compère, U. ulna (Nitzsch) Compère, U. ungeriana (Grunow) Compère among others.