Stipa arida M. E. Jones

Stipa arida M. E. Jones, Proc. Calif. Acad. II. 5: 725. 1895
Slipa Mormonum Mez. Repert. Sp. Nov. 17: 209. 1921. (Type from Utah.)
Culms densely cespitose, erect, scabemlous below the nodes, 40-80 cm. tall ; sheaths glabrous or somewhat scaberulous; ligule a ciliate m.embrane about 0.5 mm. long; blades flat or involute, scabrous, 10-20 cm. long, 1-2 mm.wide when flat; panicle narrow, compact, somewhat nodding, pale or silvery, 10-15 cm. long, the branches short, appressed; glumes 8-12 mm. long, equal or the first a little longer, hyaline, scaberulous, acuminate, the f rst 3-nered, the second 5-nerved; lemma about 5 mm. long, paleor light-brown, the callus very sharp, about 0.5 ram. long, barbed with whitish hairs, the body narrow, villous with appressed white hairs except the narrowed slightly roughened sumrnit, more or less glabrate on the sides, the summit naked or sparsely ciliate; awn 4-6 cm. long, capillary, scaberulous, loosely twisted for 1-2 cm., not twisted but flexuous beyond, sometimes obscurely once or twice geniculate; palea half as long as lemma.
Type LOCALrTv: Marysville. Utah (Jones 5377).
Distribution: Rocky slopes, Colorado, Utah, and New Mexico.

Perennials, Terrestrial, not aquatic, Stems nodes swollen or brittle, Stems erect or ascending, Stems caespitose, tufted, or clustered, Stems terete, round in cross section, or polygonal, Stem internodes hollow, Stems with inflorescence less than 1 m tall, Stems, culms, or scapes exceeding basal leaves, Leaves mostly basal, below middle of stem, Leaves mostly cauline, Leaves conspicuously 2-ranked, distichous, Leaves sheathing at base, Leaf sheath mostly open, or loose, Leaf sheath smooth, glabrous, Leaf sheath and blade differentiated, Leaf blades linear, Leaf blades very narrow or filiform, less than 2 mm wide, Leaf blades mostly flat, Leaf blade margins folded, involute, or conduplicate, Leaf blades mostly glabrous, Leaf blades scabrous, roughened, or wrinkled, Ligule present, Ligule an unfringed eciliate membrane, Inflorescence terminal, Inflorescence a contracted panicle, narrowly paniculate, branches appressed or ascending, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Flowers bisexual, Spikelets pedicellate, Spikelets dorsally compressed or terete, Spikelet less than 3 mm wide, Spikelets with 1 fertile floret, Spikelets solitary at rachis nodes, Spikelets all alike and fertille, Spikelets bisexual, Spikelets disarticulating above the glumes, glumes persistent, Spikelets disarticulating beneath or between the florets, Rachilla or pedicel glabrous, Glumes present, empty bracts, Glumes 2 clearly present, Glumes equal or subequal, Glumes equal to or longer than adjacent lemma, Glumes 3 nerved, Lemma 5-7 nerved, Lemma body or surface hairy, Lemma apex acute or acuminate, Lemma distinctly awned, more than 2-3 mm, Lemma with 1 awn, Lemma awn 2-4 cm long or longer, Lemma awned from tip, Lemma awn twisted, spirally coiled at base, like a corkscrew, Lemma awn twice geniculate, bent twice, Lemma margins inrolled, tightly covering palea and caryopsis , Lemma straight, Callus or base of lemma evidently hairy, Callus hairs shorter than lemma, Palea present, well developed, Palea membranous, hyaline, Palea shorter than lemma, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis, Caryopsis ellipsoid, longitudinally grooved, hilum long-linear.

Achnatherum aridum is a species of grass known by the common name Mormon needlegrass. It is native to the southwestern United States from the Mojave Desert in California east to Colorado and New Mexico.