Plants perennial; cespitose, sometimes rhizomatous. Culms 30-200 cm, basal internodes occasionally globose. Sheaths open, not overlapping; auricles absent; ligules membranous, sometimes ciliate; blades flat or convolute. Inflorescences terminal, narrow panicles; branches spreading until after anthesis, then becoming loosely appressed to the rachises; disarticulation above the glumes, the florets falling together, rarely above the glumes and between the florets. Spikelets laterally compressed, with 2 florets, lower florets staminate, upper florets pistillate or bisexual, a rudimentary floret occasionally present distally; rachillas pubescent. Glumes unequal, hyaline; lower glumes less than 3/4 the length of the upper glumes, 1- or 3-veined; upper glumes 3-veined; calluses short, blunt, pubescent; lower lemmas membranous, 3-7-veined, acute, awned below the middle, awns twisted and geniculate; upper lemmas membranous to subcoriacous, glabrous or hairy, 7-veined, acute, usually unawned, sometimes awned from near the apices with short, straight awns, or rarely awned similarly to the lower lemmas; paleas subequal to the lemmas, apically notched, 2-veined, 2-keeled, keels scabrous or hairy; lodicules 2, free, linear, membranous, glabrous, entire; anthers 3, 3.4-6.5 mm; ovaries pubescent. Caryopses not grooved, dorsally compressed to terete, hairy; hila long-linear. x = 7. Name from the Greek arren, masculine, and ather, awn, referring to the awned staminate florets.

Arrhenatherum is a Mediterranean and eastern Asian genus of six species; one has become established in North America.

1.   Arrhenatherum elatius (L.) P. Beauv. ex J. Presl & C. Presl
Tall Oatgrass, Fenasse, Fromental

Plants loosely cespitose, sometimes rhizomatous, rhizomes to 3 mm thick. Culms 50-140(180) cm, erect, glabrous, unbranched, basal internodes swollen or not swollen; nodes glabrous or occasionally puberulent to densely hairy. Sheaths smooth; ligules 1-3 mm, obtuse to truncate, usually ciliate; blades 5-32 cm long, (1)3-8(10) mm wide, flat, glabrous or rarely shortly pilose, sometimes scabrous. Panicles 7-30(36) cm long, 1-6(10) cm wide, green, shiny, becoming stramineous, sometimes purple-tinged; branches 15-20 mm, ascending to divergent, verticillate, usually spikelet-bearing to the base; pedicels 1-10 mm. Spikelets 7-11 mm; rachilla internodes to 0.7 mm, stout; rachilla prolongations 1.2-2 mm long, slender, apices often with a small, club-shaped rudiment. Glumes lanceolate to elliptic; lower glumes 4-7 mm; upper glumes 7-10 mm; callus hairs to 3.7 mm; lemmas (4)7-10 mm, apices bifid; awns of lower lemmas 10-20 mm, twisted below, often with alternating light and dark bands; awns of upper lemmas absent or to 5 mm long and arising just below the apices, rarely to 15 mm long and arising from above the middle; paleas 0.5-1 mm shorter than the lemmas, acute; anthers 3.6-5(6) mm. Caryopses 4-5 mm long, about 1.2 mm wide, ellipsoid, densely hairy, yellowish. 2n = 14, 28, 42.

Arrhenatherum elatius is grown as a forage grass and yields a palatable hay; it does not withstand heavy grazing. It readily escapes from cultivation and can be found in mesic to dry meadows, the edges of woods, streamsides, rock outcrops, and disturbed areas such as fields, pastures, fence rows, and roadsides. Varigated forms with the leaves striped green and white or yellow are cultivated as ornamentals. There are two subspecies, both of which have been found in the Flora region. Plants in which both lemmas have long, geniculate awns have been called A. elatius var. biaristatum (Peterm.) Peterm., but do not merit formal taxonomic recognition.

Arrhenatherum elatius subsp. elatius is more common than subsp. bulbosum. It is not known whether the two have different ecologic or geographic distributions in North America.

While both can be weedy, Arrhenatherum elatius subsp. bulbosum (Willd.) Schübl. & G. Martens is especially difficult to control in cultivated fields, as tilling the soil spreads the swollen internodes, which then propagate vegetatively.