Plants annual or perennial; sometimes rhizomatous, sometimes cespitose. Culms 5-150 cm, glabrous or pubescent, basal branching extravaginal. Sheaths open the entire length or fused at the base; auricles absent; ligules membranous, often erose to lacerate, sometimes ciliolate; blades rolled in the bud. Inflorescences terminal panicles, open and diffuse to dense and spikelike; branches antrorse-scabrous. Spikelets (2.4)4-9 mm, usually subsessile to pedicellate, rarely sessile, laterally compressed, with 2-5 florets; reduced florets (if present) distal; rachillas hairy, internodes evident, prolonged beyond the distal bisexual florets; disarticulation usually above the glumes and between the florets, subsequently below the glumes, in some species initially below the glumes. Glumes subequal or unequal, keels scabrous, apices usually acute and unawned, often apiculate; lower glumes 1(3)-veined; upper glumes 3(5)-veined, lateral veins less than 1/2 the glume length; calluses hairy; lemmas 3-7-veined, margins hyaline, unawned or awned from above the middle with a single awn, apices usually bifid, sometimes entire; paleas subequal, equal to, or longer than the lemmas, membranous, 2-veined, veins usually extended as bristlelike tips; lodicules 2, shallowly and usually slenderly lobed to fimbriate; anthers 3; ovaries glabrous or pubescent; styles 2. Caryopses elongate-fusiform, compressed, brown; embryos elliptic, to 1/3 the length of the caryopses; endosperm milky. x = 7. Name from the Latin tres, three, and seta, bristle, alluding to the three-awned appearance of the lemmas of the type species, Trisetum flavescens.

Trisetum, a genus of approximately 75 species, occurs primarily in temperate, subarctic, and alpine regions. Eight species are native to the Flora region; two have been introduced, one of which is not known to have persisted. Trisetum usually differs from Sphenopholis, with which it occasionally hybridizes, in having longer awns that are inserted lower on the lemmas and spikelets that disarticulate above the glumes. It differs from Deschampsia in its more acute, bifid lemmas and in having the awns inserted at or above the midpoint of the lemmas.

Trisetum spicatum is important as forage on native rangelands. Like other species of the genus, it is a significant component of natural food pyramids, especially in arctic and alpine regions and in mountain parks. Trisetum flavescens was introduced from Europe as a pasture grass; T. interruptum is often weedy.

As of May 2007, Trisetum projectum is now considered to be a separate species, instead of being included as a synonym for Trisetum canescens.

1.   Trisetum melicoides (Michx.) Scribn.
False Melic, Trisèe Fausse-Mélique

Plants perennial, with both fertile and sterile shoots; cespitose. Culms (20)40-80(100) cm, erect, smooth or scabridulous. Leaves concentrated below midlength on the culms; sheaths glabrous or pilose; ligules 1.5-3.5 mm, rounded or truncate; blades 10-20+ cm long, 2-9 mm wide, flat, lax. Panicles 8-20 cm long, usually 2-4 cm wide, lax, nodding, silvery-green or -tan; lower branches to 5 cm, ascending, naked below, the spikelets imbricate distally. Spikelets 5-7(9) mm, pedicellate, lance-ovate, with 2(4) florets; rachilla internodes and hairs 1.3-2 mm. Glumes unequal, widest at or below the middle; lower glumes 4-5.5 mm; upper glumes 5-7 mm long, nearly equaling the florets, wider than the lower glumes; callus hairs 1.5-2 mm; lemmas 5-6 mm, smooth or scabridulous, apices usually minutely bifid, sometimes entire, awns absent or to 2 mm, arising just below and rarely exceeding the apices; paleas shorter than the lemmas; anthers 0.6-0.8 mm. Caryopses about 3 mm, sparsely pubescent distally. 2n = 14.

Trisetum melicoides is a native species that grows in moist, cool stream banks, on gravelly shores, shaded rock ledges (especially calcareous ones), and in damp woods. It grows in southeastern Canada and the northeastern United States. It is listed as endangered in Wisconsin, New York, and Maine. Plants with pilose sheaths have been called T. melicoides var. majus (A. Gray) Hitchc., but the trait varies within populations.

2.   Trisetum wolfii Vasey
Wolf's Trisetum

Plants perennial, with both fertile and sterile shoots; shortly rhizomatous. Culms 20-80(100) cm, erect, glabrous or retrorsely pubescent below the nodes. Leaves usually concentrated on the lower 1/3 of the culms; sheaths glabrous, scabridulous, or sparsely retrorse-pilose; ligules (1.2)2.5-4(6) mm, truncate to rounded; blades to 15 cm long, 2-7 mm wide, flat, ascending, lax, smooth, scabrous, or sparsely pilose, often involute near the sometimes prowlike apices. Panicles (10)20-40(50) cm long, usually 1-1.5 cm wide, stiffly erect, green, tan, or purple-tinged; branches appressed-ascending, the spikelets evenly distributed. Spikelets 4-7(8) mm, usually subsessile, rarely on pedicels to 4 mm, ovate, with 2(3) florets; rachilla internodes 1.5-2 mm; rachilla hairs to 1 mm. Glumes subequal, usually exceeding the lowest florets; lower glumes 4-7 mm; upper glumes 4-6.5 mm long, a little wider than the lower glumes; callus hairs less than 0.5 mm; lemmas 4-6.5 mm, lanceolate, firmer than the glumes, scabridulous-puberulent, obscurely bifid, awns absent or to 2 mm, arising just below and rarely exceeding the apices; paleas shorter than the lemmas; anthers (0.6)1(1.5) mm. Caryopses to 3 mm, pubescent. 2n = 14.

Trisetum wolfii grows in moist meadows, marshes, and stream banks in aspen groves and parks in the spruce-fir forest zone, at medium to high, but usually not alpine, elevations.It is native to southwestern Canada and the western United States.

3.   Trisetum orthochaetum Hitchc.
Bitterroot Trisetum

Plants perennial, with both fertile and sterile shoots; shortly rhizomatous. Culms 80-110 cm, solitary, decumbent, often anthocyanic at the base, glabrous. Leaves evenly distributed; sheaths usually glabrous; ligules 3-5 mm, truncate or rounded, erose; blades 8-20 cm long, 3-7 mm wide, flat, lax, scabrous. Panicles 13-20 cm, narrow, moderately dense, nodding, pale green and slightly tinged with purple; branches loosely ascending, naked below for 1-2 cm, the spikelets closely and evenly distributed distally. Spikelets 7-9 mm, subsessile or on pedicels to 1 cm, oblong-ovate, with 2-3(4) florets; rachilla internodes to 2 mm; rachilla hairs about 1 mm. Glumes lanceolate or oblanceolate; lower glumes about 5.5 mm long, about 1 mm wide, widest near the base, slenderly acuminate; upper glumes to 6.3 mm long, about 2 mm wide at or just above the middle, acuminate; lemmas 5-6.5 mm long, about 1/3 as wide as long, apices bifid, teeth less than 1 mm, awned, awns 4-6 mm, arising about 1 mm below the teeth, not twisted basally, straight or flexuous; paleas almost equaling the lemmas; callus hairs about 0.5 mm; anthers minute or to 1 mm, appearing non-functional; ovaries pubescent. Caryopses to 2.5 mm, malformed. 2n = unknown.

Trisetum orthochaetum is known only from Montana, in or near the edges of marshes, seeps, and creeksides, at about 1465 m. It may be a sterile hybrid between T. canescens and T. wolfii (Shelly 1987).

4.   Trisetum canescens Buckley
Tall Trisetum

Plants perennial, sometimes with both fertile and sterile shoots; cespitose, not rhizomatous. Culms 40-120 cm, erect, usually smooth. Leaves 3-4 per culm; sheaths crisped-pubescent to shaggy-pilose, scabrous or smooth; ligules (1.5)3-6 mm, rounded to truncate; blades 10-30 cm long, (3)7-10 mm wide, flat, erect, lax, margins (and occasionally surfaces) sometimes with scattered 1-3 mm hairs. Panicles 10-25 cm long, (0.75)1-3(4) cm wide, narrow, erect or nodding at the apices, green or tan, occasionally purple-tinged; branches 1-5.5 cm, ascending to somewhat divergent, most spikelet-bearing for their full length, sometimes the lowermost branches naked below. Spikelets 7-9 mm, pedicellate, with 2-4 florets; rachilla internodes 1.5-3 mm; rachilla hairs 0.7-1 mm; disarticulation above the glumes and between the florets. Glumes unequal to subequal; lower glumes 3-5 mm, narrow, lanceolate to subulate, acute or long-tapered; upper glumes (3.5)5-7(9) mm long, shorter than the lowest florets, at least twice as wide as the lower glumes, broadly lanceolate to obovate, widest at or below the middle, tapering to the apices, acute; callus hairs about 0.5 mm; lemmas 5-7 mm, glabrous, apices bifid, teeth to 2.5(3.2) mm, setaceous, awned, awns 7-14 mm, arising mostly at the upper 1/3 of the lemmas, geniculate; paleas as long as or slightly longer than the lemmas; anthers 1-3 mm. Caryopses usually to 3 mm, glabrous or finely hairy distally. 2n = 28, 42.

Trisetum canescens grows at or near stream banks, and in forest margins or interiors, in moist to dry areas in the western Flora region. It is especially abundant in ponderosa pine stands and spruce-fir forests. The vestiture of different parts varies throughout the range of the species. Plants from California with conspicuously interrupted panicles have been called Trisetum cernuum var. projectum (Louis-Marie) Beetle.

5.   Trisetum cernuum Trin.
Nodding Trisetum

Plants perennial, with both fertile and sterile shoots; cespitose, not rhizomatous. Culms (30)50-110 cm, erect, glabrous or pubescent. Leaves 2-3 per culm; sheaths scabridulous or pilose; ligules 1.5-3 mm, truncate, erose to lacerate; blades (8.5)15-20+ cm long, (3)7-12 mm wide, flat, ascending, lax at maturity, often scabridulous. Panicles 10-30 cm long, (1)2-9 cm wide, open, nodding, green or tan, occasionally purple-tinged; branches 2-12+ cm, most, except sometimes the uppermost, spikelet-bearing only towards the apices, with the basal (1/5)1/3-1/2 bare, filiform, flexuous, at least the lowermost 1-3 whorls spreading or drooping. Spikelets 6-12 mm, subsessile to pedicellate, pedicels to 2 cm, usually with 2-3 functional florets below 1-2 reduced florets; rachilla internodes and hairs 1-2.5 mm; disarticulation above the glumes and between the florets. Glumes unequal; lower glumes 0.75-2(3) mm, subulate; upper glumes 3.5-5 mm long, shorter than the lowest florets, 2-3 times as wide as the lower glumes, widest at or above the middle, ovate or obovate, rounded to the acuminate apices; callus hairs to 1 mm; lemmas 5-6 mm, broadly lanceolate, glabrous, bifid, teeth to 1.3 mm, awned, awns (7)9-14 mm, arising from above midlength to just below the teeth, conspicuous, arcuate to flexuous; paleas shorter than the lemmas; anthers about 1 mm. Caryopses about 2.5-3.2 mm, densely to sparsely pubescent. 2n = 42.

Trisetum cernuum grows in moist woods, stream banks, lake and pond shores, and floodplains of the western Flora region. The hairiness of the leaf sheaths varies, often within a plant.

6.   Trisetum flavescens (L.) P. Beauv.
Yellow Oatgrass, Avoine Jaunâtre

Plants perennial, sometimes with both fertile and sterile shoots; usually cespitose, sometimes rhizomatous, rhizomes usually short, to 7 cm in sandy soils. Culms(10)50-80(130) cm, erect or decumbent, glabrous, sometimes scabrous or pubescent near the upper nodes. Leaves usually evenly distributed; sheaths glabrous or pilose, throats often with 2+ mm hairs; ligules 0.5-1(2) mm, obtuse, lacerate, sometimes ciliolate, with hairs to 0.5 mm; blades 5-15(18) cm long, 1.5-4(6) mm wide, flat or involute, lax, pubescent or pilose. Panicles 5-20 cm long, 1.5-7 cm wide, erect or nodding, glistening yellowish-brown, sometimes purple-tinged or variegated; branches 2-4(6) cm, ascending to divergent, often flexuous, sometimes naked below. Spikelets 4-8 mm, subsessile or on pedicels to 5 mm, with (2)3(4) florets; rachilla internodes to 1 mm or longer; rachilla hairs to 1.5 mm; disarticulation above the glumes and between the florets. Glumes unequal, shiny; lower glumes 2.5-4.7 mm, narrowly lanceolate to subulate; upper glumes 4-7 mm long, equaling or longer than the lowest florets, twice as wide as the lower glumes, lance-elliptic, acute; callus hairs to 0.5 mm; lemmas 3.5-6.3 mm, ovate-lanceolate, minutely pubescent, bifid or bicuspidate, teeth extended into conspicous, usually 3-6 mm bristles, awned, awns (3)5-9 mm, arising from the upper 1/3 of the lemmas, geniculate, tightly twisted below; paleas 3-5.5 mm; anthers 1.3-2.8 mm. Caryopses to 2.5-3 mm, glabrous. 2n = 28.

Trisetum flavescens grows in seeded pastures, roadsides, and as a weed in croplands. Native to Europe, west Asia, and north Africa, it was introduced into the Flora region because of its drought resistance, wide soil tolerance, and high palatability to domestic livestock. It is one of the few range plants known to contain calcinogenic glycosides, which can lead to vitamin D toxicity in grazing animals (Dixon 1995). This species seems not to have persisted in southern Ontario (Michael Oldham, pers. comm.). Several infraspecific taxa have been recognized; no attempt has been made to determine which are present in the Flora region.

7.   Trisetum spicatum (L.) K. Richt.
Spike Trisetum, Trisète à Épi

Plants perennial, with both fertile and sterile shoots; cespitose, not rhizomatous. Culms 10-120 cm, erect, usually glabrous, sometimes scabridulous or villous. Leaves mostly basal or evenly distributed; sheaths variously pubescent or glabrous; ligules 0.5-4 mm, truncate or rounded; blades (3)10-20(40) cm long, 1-5 mm wide, flat, folded, or involute, erect and stiff or ascending and lax. Panicles (5)20-30(50) cm long, (0.5)1-2.5(5) cm wide, from spikelike to open, often interrupted basally, green, purplish, or tawny, usually silvery-shiny; branches with the spikelets evenly distributed. Spikelets 5-7.5 mm, sessile, subsessile, or on pedicels to 1.5(3.5) mm, with 2(3) florets; rachilla internodes 0.5-1.5 mm; rachilla hairs to 1 mm. Glumes subequal to unequal, lanceolate, usually smooth, sometimes scattered scabrous or pilose, with wide scarious margins, apices acute to acuminate, sometimes apiculate; lower glumes 3-4(5.5) mm; upper glumes 4-7 mm long, equaling or exceeding the lowest florets, less than twice as wide as the lower glumes; callus hairs to 1 mm; lemmas 3-6(7) mm, narrowly to broadly lanceolate, glabrous, scabridulous, or pilose, apices bifid, teeth usually less than 1 mm, awned, awns 3-8 mm, arising from the upper 1/3 of the lemmas, geniculate, twisted basally; anthers 0.7-1.4 mm. Caryopses 1.5-3(4) mm, glabrous. 2n = 14, 28, 42.

Trisetum spicatum grows in moist meadows, forests, rock ledges, and tundra slopes and screes, at 0-4300 m. Its range includes both North and South America and Eurasia. Many infraspecific taxa have been based on the variation in vestiture and openness of the panicle, but none appears to be justified (see Finot et al. 2004 for a different opinion). Trisetum montanum Vasey appears to represent no more than an extreme phase. Trisetum spicatum differs from T. sibiricum in its pubescent sheaths and denser, usually narrower panicles.

8.   Trisetum sibiricum Rupr.
Siberian Trisetum

Plants perennial, sometimes with both fertile and sterile shoots; rhizomatous. Culms 15-40(65) cm, solitary, decumbent; nodes glabrous. Sheaths smooth; ligules 1-3.5 mm, truncate or slightly higher in the center, often lacerate; blades 8-15(24) cm long, 2.5-7 mm wide, flat, erect or ascending, stiff or lax, smooth. Panicles 2-12(16) cm long, (1)2-3(6) cm wide, ovate-spicate, sometimes basally interrupted, yellowish-brown, often mottled, shiny; branches mostly 0.1-2(4) cm, appressed-ascending, the spikelets distal; disarticulation above the glumes. Spikelets 5-8 mm, subsessile or pedicellate, pedicels to 4 mm, with 2(3) florets; rachilla internodes usually 1-2 mm; rachilla hairs 0.5-1 mm, often curly and tangled. Glumes lanceolate, glabrous; lower glumes 3-4.5 mm; upper glumes 5-8 mm; callus hairs about 0.5 mm; lemmas 4.5-7 mm, glabrous, apices minutely bifid, awned, awns 4-10+ mm, arising from the upper 1/3, exceeding the lemmas, flexuous, curved, or bent and twisted basally; paleas equal or subequal to the lemmas; anthers about 2-3.5 mm. Caryopses 1-2 mm, ovate, smooth, brown. 2n = 14, 28.

Trisetum sibiricum grows on coastal beaches, creek banks, and in moist meadows and open forests, from sea level to 300 m or higher; it is often abundant where it occurs and has significant value as a pasture plant. Circumpolar in distribution, in the Flora region it grows in Alaska and the Yukon Territory. Most North American plants belong to T. sibiricum subsp. litorale Rupr. ex Roshev., having culms 15-30 cm tall, leaf blades 2.5-4 mm wide, panicles 3-5 cm long and 2-3 cm wide, branches to 2 cm long, and lemma awns 5-8 mm long. Trisetum sibiricum Rupr. subsp. sibiricum occurs in the Yukon Territory and Eurasia. It differs from T. spicatum in its smooth culms and leaves, and its broad, less dense panicles.

9.   Trisetum interruptum Buckley
Prairie Trisetum

Plants annual, without sterile shoots; tufted. Culms (5)10-40(60) cm, erect or spreading, mostly glabrous, pilose below the nodes. Leaves basally concentrated; sheaths scabridulous or pilose; ligules 1-2.5 mm, truncate; blades 3-12 cm long, 1-4 mm wide, flat, folded, or involute distally when dry, ascending, glabrous or pubescent, margins frequently scattered-ciliate. Panicles 2-15 cm long, 0.3-1.5 cm wide, often interrupted, at least in the lower 1/3, green or tan; branches short, usually erect to appressed, the spikelets crowded. Spikelets 3.5-6 mm, often in pairs with 1 subsessile and 1 pedicellate, with 2-3 florets; disarticulation initially above the glumes, subsequently below; rachilla internodes usually 0.8-1 mm; rachilla hairs usually about 0.5 mm. Glumes subequal, 4-5 mm, about as long as the lowest lemmas, smooth or scattered-scabridulous; lower glumes 0.5-1 mm wide, lanceolate or elliptical, 3-veined, acuminate, sometimes apiculate; upper glumes about twice as wide as the lower glumes, elliptical or oblanceolate, acuminate; callus hairs 0.1-0.2(0.5) mm, sparse; lemmas 3-4.5 mm, usually glabrous, sometimes minutely pustulate-scabridulous, apices bifid, teeth to 1.7 mm, awned, awns usually 4-8 mm, arising from midlength to just below the teeth, geniculate, twisted basally (rarely 2-4 mm, straight, arcuate, or flexuous); paleas usually 2/3 as long as the lemmas, hyaline; anthers about 0.2 mm. Caryopses 2-3 mm, longitudinally striate, sometimes with a few hairs distally. 2n = 14.

Trisetum interruptum grows in open, dry or moist soil in deserts, plains, arid shrublands, and riparian woodlands, from the southern United States into Mexico. It is often weedy.

10.   Trisetum aureum (Ten.) Ten.
Golden Oatgrass

Plants annual, without sterile shoots; tufted. Culms 7-30 cm, glabrous, erect, spreading, or geniculate. Sheaths somewhat inflated, glabrous or villous; blades to 10 cm long, to 3 mm wide, flat, subglabrous to villous. Panicles 1-5 cm long, 0.5-3.0 cm wide, pyramidal to ovoid, dense, shining yellowish to tan. Spikelets 2.5-3.5 mm, with 2-3 florets. Glumes unequal; lower glumes 2-2.5 mm long, narrower than the upper glumes, 1-veined; upper glumes 2.5-3 mm, 3-veined; callus hairs 0.3-0.4 mm; lemmas 1.6-2.7 mm, glabrous or hairy, with wide hyaline margins, apices bifid, teeth to about 0.5 mm, awned, awns 2-6 mm, arising from somewhat above the middle of the lemmas, slightly bent; anthers 1-1.5 mm. 2n = unknown.

Trisetum aureum is native to the Mediterranean region. It was collected from a ballast dump in Camden, New Jersey, in 1896 (Hitchcock 1951), and has not been reported since from the Flora region.