Trisetum orthochaetum Hitchc.

Trisetum orthochaetum Hitchc. Am. Jour. Bot. 21: 134. 1934
Perennial; culms solitary, erect, slender, 110 cm. tall; sheaths glabrous; blades flat, scabrous, 8-20 cm. long, 3-7 mm. wide; panicle slightly nodding, lax, pale, about 18 cm. long, the filiform branches loosely ascending, naked below, the lower fascicled, as much as 8 cm. long; spikelets short-pediceled, somewhat appressed, mostly 3-flowered, 8-9 mm. long excluding the awns, the rachilla appressed-silky ; glumes acuminate, about 6 mm. long, the second one wider; lemmas rounded on the back, minutely scaberulous on the upper part, obscurely 5-nerved, the callus short-pilose, the apex acute, erose-toothed, awned about 2 mm. below the tip, the awn straight or nearly so, exceeding the lemma about 3 mm.
Type locality: Lolo Hot Springs, Bitterroot Mountains, Montana {Chase 5129). Distribution: Known only from the type locality.

Perennials, Terrestrial, not aquatic, Rhizomes present, Rhizome short and compact, stems close, Stems nodes swollen or brittle, Stems erect or ascending, Stems solitary, 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 with inflorescence 1-2 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 2-10 mm wide, Leaf blades mostly flat, Leaf blades more or less hairy, 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 a dense slender spike-like panicle or raceme, branches contracted, Inflorescence solitary, with 1 spike, fascicle, glomerule, head, or cluster per stem or culm, Inflorescence branches more than 10 to numerous, Lower panicle branches whorled, Flowers bisexual, Spikelets pedicellate, Spikelets sessile or subsessile, Spikelets laterally compressed, Spikelet less than 3 mm wide, Spikelets with 2 florets, 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 hairy, Glumes present, empty bracts, Glumes 2 clearly present, Glumes equal or subequal, Glumes equal to or longer than adjacent lemma, Glumes keeled or winged, Glumes 1 nerved, Glumes 3 nerved, Lemma similar in texture to glumes, Lemma 5-7 nerved, Lemma glabrous, Lemma body or surface hairy, Lemma apex dentate, 2-fid, Lemma distinctly awned, more than 2-3 mm, Lemma with 1 awn, Lemma awn less than 1 cm long, Lemma awned from tip, Lemma awn from sinus of bifid apex, Lemma awn subapical or dorsal, Lemma awns straight or curved to base, Lemma margins thin, lying flat, Lemma straight, Callus or base of lemma evidently hairy, Callus hairs shorter than lemma, Palea present, well developed, Palea membranous, hyaline, Palea longer than lemma, Palea 2 nerved or 2 keeled, Stamens 3, Styles 2-fid, deeply 2-branched, Stigmas 2, Fruit - caryopsis.

Trisetum orthochaetum là một loài thực vật có hoa trong họ Hòa thảo. Loài này được Hitchc. miêu tả khoa học đầu tiên năm 1934.