A perennial grass, with soft flat leaf-blades and an open panicle. Spikelets usually 2-flovvered. Two lower scales empty, thin-membranous, much shorter than the flowering ones, unequal, rounded or obtuse at the apex; flowering scales membranous, erose-truncate. Palet barely shorter than the scale. Stamens 3. Styles distinct. Stigmas plumose. [Greek, in allusion to the erose top of the flowering scales.]

A monotypic genus of arctic and mountainous regions of the northern hemisphere. Type species: Aira aquatica L.

1. Catabrosa Aquatica (L.) Beauv. Water Whorl-Grass

Fig. 590

Aira aquatica L. Sp. PI. 64. 1753.

Catabrosa aquatica Beauv. Agrost. 157. 1812.

Smooth and glabrous, culms 4'-2° tall, erect, from a creeping base, bright green, flaccid. Sheaths usually overlapping, loose; ligule 1 1/2"-2 1/2" long; blades 1 1/2'- 5' long, 1"-3" wide, flat, obtuse; panicle 1'-8' in length, open, the branches whorled, spreading or ascending, very slender, 1/2'-2' long; 'spikelets 1 1/4"- 1 3/4" long, the empty scales rounded or obtuse, the first about half as long as the second, which is crenulate on the margins; flowering scales 1"- 1 1/4" long, 3-nerved, erose-truncate at the apex.

In water or wet soil, Labrador and Newfoundland to Alaska, south to Nova Scotia, Nebraska and Colorado. Also in Europe and Asia. Water-grass, Water Hair-grass. Summer.