Plants usually perennial; herbaceous, usually cespitose, occasionally rhizomatous. Culms 10-150 cm, not woody, sometimes branched above the base; internodes usually pith-filled, sometimes hollow. Leaves sometimes predominantly basal, sometimes predominantly cauline; sheaths open; auricles lacking; ligules of hairs or very shortly membranous and long-ciliate, the 2 types generally indistinguishable. Inflorescences terminal, usually panicles, sometimes racemes, occasionally spikes; primary branches without axillary pulvini and usually appressed to ascending, or with axillary pulvini and ascending to strongly divergent or divaricate. Spikelets with 1 floret; rachillas not prolonged beyond the florets; disarticulation above the glumes. Glumes often longer than the florets, thin, usually 1-3-veined, acute to acuminate; florets terete or weakly laterally compressed; calluses well-developed, hirsute; lemmas fusiform, 3-veined, convolute, usually glabrous or scabridulous, usually enclosing the palea at maturity, usually with 3 terminal awns, lateral awns reduced or obsolete in some species, lemma apices sometimes narrowed to a straight or twisted beak below the awns; awns ascending to spreading, usually straight, bases sometimes twisted together into a column or the bases of the individual awns coiled, twisted, or otherwise contorted, occasionally disarticulating at maturity; paleas shorter than the lemmas, 2-veined, occasionally absent; anthers 1 or 3. Caryopses fusiform; hila linear. x = 11, 12. Name from the Latin arista, awn.

Aristida is a tropical to warm-temperate genus of 250-300 species. It grows throughout the world in dry grasslands and savannahs, sandy woodlands, arid deserts, and open, weedy habitats and on rocky slopes and mesas. All 29 species in this treatment are native to the Flora region.

The divergent awns aid in wind and animal transportation of the florets and, by holding the florets and the caryopses they contain at an angle to the ground, in establishment. The presence of Aristida frequently indicates soil disturbance or abuse. Although generally poor forage grasses and, because of the calluses, potentially harmful to grazing animals, some species of Aristida are an important source of spring forage on western rangelands. Quail and small mammals eat small amounts of the seed.

NOTE: Lemma lengths are measured from the base of the callus to the divergence of the awns.

1.   Aristida desmantha Trin. & Rupr.
Curly Threeawn

Plants annual. Culms (30)45-80 cm, branching at the lower nodes, often diffusely so; nodes and internodes glabrous. Leaves cauline; sheaths shorter or slightly longer than the internodes, glabrous or with straight hairs, sometimes pilose-floccose; collars glabrous or pilose at the sides; ligules about 0.5 mm; blades (6)10-20 cm long, 1-2(3) mm wide, yellow-green, turning reddish late in the season, involute to loosely folded, abaxial surfaces smooth or scabrous near the base, sometimes pubescent distally, adaxial surfaces usually glabrous, sometimes scabrous or pubescent, lateral veins about twice as thick as the inner veins. Inflorescences paniculate, 10-20 cm long, 2-7 cm wide; rachis nodes glabrous; primary branches stiffly ascending, with axillary pulvini, with 3-9 spikelets. Spikelets in fan-shaped clusters, pedicels with axillary pulvini. Glumes about equal, 10-17 mm, light to dark brown, glabrous or rarely sparsely pilose, 1-veined, apices cleft and awned, awns 2-5 mm; calluses 1-2.5 mm; lemmas 7-10 mm, gray to light brown, narrowing to a 2-5(7) mm beak, junction of the lemma and awns evident; awns 20-28 mm, similar in length, curved to strongly arcuate near the base, not forming a column, straight and divergent distally, disarticulating at maturity; anthers 3, 1-2 mm, dark purple. Caryopses 7-8 mm, smooth, chestnut brown. 2n = unknown.

Aristida desmantha grows in sandy fields, dry pine woods, and waste places in the United States. It is generally similar to A. tuberculosa, but has shorter glumes, calluses, and awns.

2.   Aristida tuberculosa Nutt.
Seaside Threeawn

Plants annual. Culms (25)40-100 cm, erect or decumbent to ascending near the base, highly branched above the base; nodes and internodes glabrous. Leaves cauline; sheaths usually slightly shorter than the internodes, glabrous or pilose; collars often with a line of tangled hairs; ligules about 0.5 mm; blades 8-25 cm long, 2-4 mm wide, light green, flat to loosely involute, glabrous and smooth abaxially, scabridulous adaxially. Inflorescences paniculate, 10-20 cm long, 3-10 cm wide; rachis nodes glabrous, scabrous, or strigose; primary branches 1-4 cm, stiffly ascending, with axillary pulvini, with 1-4 spikelets per branch. Spikelets loosely congested. Glumes 20-30 mm, yellowish-brown, 1-veined, apices narrowing to a 5-10 mm awn; upper glumes slightly longer than the lower glumes; calluses 3-4 mm; lemmas 10-14 mm, dark and mottled at maturity, glabrous or occasionally sparsely pubescent, not beaked, junction of the lemma and awns evident; awns twisted together basally into a 8-15 mm column, free portions 30-40 mm, those of the central and lateral awns similar in length, strongly curved to arcuate near the base, straight and strongly divergent to reflexed distally, disarticulating at the base of the column at maturity; anthers 3, about 2.5 mm, brownish. Caryopses 8-10 mm, dark brown. 2n = unknown.

Aristida tuberculosa grows in sandy fields, hills, pinelands, and disturbed areas. Along the Atlantic coastal fringe, it grows on maritime dunes; inland it is associated with xeric pine-oak sandhills. It is generally similar to A. desmantha, but has longer glumes, calluses, and awns. Like A. desmantha, A. tuberculosa is restricted to the United States.

3.   Aristida californica Thurb.
Mojave Threeawn

Plants perennial; sometimes flowering the first year. Culms 10-40 cm, highly branched above the base in age; internodes glabrous or pubescent, sometimes nearly lanose. Leaves cauline; sheaths shorter than the internodes, glabrous or puberulent; collars glabrous or pubescent at the sides; ligules 0.5-1 mm; blades usually less than 6 cm long, 0.5-1 mm wide, pale green, involute, glabrous or puberulent abaxially. Inflorescences paniculate or racemose, 5-10 cm long, 1-2 cm wide, with few spikelets; rachis nodes glabrous or with straight hairs; primary branches 1-2 cm, appressed, without axillary pulvini. Spikelets appressed. Glumes unequal, 1-2-veined; lower glumes 4-10 mm; upper glumes 7-15 mm; calluses about 1 mm; lemmas 5-7 mm, purple or mottled, junction of the lemma and awns evident; awns twisted together basally into a 4-26 mm column, free portions 12-50 mm, those of the central and lateral awns similar in length, curved to arcuate basally, straight and divergent distally, disarticulating at the base of the column at maturity; anthers 3, about 2 mm long. 2n = 22.

The range of both varieties of A. californica extends from the southwestern United States into northwestern Mexico.

Aristida californica Thurb. var. californica

Cauline internodes puberulent to nearly lanose. Lower glumes 6-10 mm; upper glumes 11-13 mm; awns forming a 7-26 mm column, free portions 25-50 mm.

Aristida californica var. californica grows in dry, sandy plains, dunes, and flats of the Sonoran and Mojave deserts at elevations of 0-700 m.

Aristida californica var. glabrata Vasey

Cauline internodes glabrous. Lower glumes 4-8 mm; upper glumes 7-15 mm; awns forming a 4-16 mm column, free portions 12-40 mm.

Aristida californica var. glabrata grows in sandy to rocky soils of desert grassland and desert thorn-scrub communities in the Sonoran and Mojave deserts at elevations of 500-1400 m, generally to the east of var. californica.

4.   Aristida patula Chapm. ex Nash
Tall Threeawn

Plants perennial; loosely cespitose, bases knotty, sometimes shortly rhizomatous. Culms (60)70-100 cm, stiffly erect, unbranched. Leaves cauline; sheaths longer than the internodes, mostly glabrous, summit with hairs; collars hispid, hairs 0.2-0.8 mm; ligules less than 0.5 mm; blades 20-55 cm long, 2-4 mm wide, light bluish-green, flat to loosely folded, glabrous abaxially, scabridulous adaxially. Inflorescences paniculate, 30-50 cm long, 15-25 cm wide; rachis nodes glabrous or with straight hairs shorter than 0.5 mm; primary branches 8-22 cm, ascending to divaricate or drooping, with axillary pulvini, basal portion without spikelets. Spikelets appressed along the branches. Glumes brown to purplish, 1-veined, with a 1-2 mm awn; lower glumes 10-13 mm, slightly longer than the upper glumes; calluses 0.5-1 mm; lemmas 10-12(15) mm, glabrous, light gray to brownish, narrowing to a beak, beak less than 7 mm, not or only slightly twisted, junction with the awns not conspicuous; awns unequal, not disarticulating at maturity; central awns 20-25 mm, straight; lateral awns 3-10 mm, to 1/2 as long as and about 1/2 as thick as the central awns, usually divergent; anthers 3, about 3 mm, yellow-green. Caryopses about 8 mm. 2n = unknown.

Aristida patula grows in sandy fields, low pinelands, and roadsides. It is endemic to Florida.

5.   Aristida floridana (Chapm.) Vasey
Florida Threeawn

Plants perennial; cespitose. Culms 70-100 cm, erect, mostly unbranched. Leaves cauline; sheaths mostly longer than the internodes, mostly glabrous, summit with hairs; collars mostly glabrous, sides usually with straight or wrinkled hairs; ligules 0.2-0.3 mm; blades 30-55 cm long, 1-2 mm wide, pale yellow-green, loosely involute, lax, glabrous abaxially, with scattered hairs adaxially. Inflorescences paniculate, 30-45 cm long, 5-25 cm wide, oblong to ovate; primary branches single or paired, ascending and somewhat lax to stiffly divergent, with weakly developed axillary pulvini, spikelet-bearing to the base; lowermost branches to 15 cm. Spikelets mostly appressed. Glumes purplish-tinged, 1-veined; lower glumes 10-14 mm; upper glumes 8-9 mm; calluses 0.5-0.7 mm; lemmas 8-12 mm, gray mottled with purple or dark patches, narrowing to a slightly curved and twisted beak, junction with the awns not strongly marked; awns not disarticulating at maturity; central awns 10-25 mm, falcate; lateral awns absent; anthers 3, about 1 mm, brown. Caryopses 6-7 mm, chestnut-colored. 2n = unknown.

Aristida floridana grows in waste places, along roadsides, and on railroad embankments. It is rare in the United States, being known only from Key West and Ramrod Key, Florida. It is more common in the Yucatan Peninsula, Mexico, where it intergrades with A. ternipes.

6.   Aristida ternipes Cav.

Plants perennial; cespitose. Culms 25-120 cm, wiry, erect to sprawling, unbranched. Leaves basal and cauline; sheaths usually longer than the internodes, glabrous; collars glabrous or strigillose; ligules less than 0.5 mm; blades 5-40 cm long, 1-2.5 mm wide, flat to folded, straight to lax at maturity, adaxial surfaces with scattered, 1.5-3 mm hairs near the ligule. Inflorescences paniculate, 15-40 cm long, (8)10-35(45) mm wide; rachis nodes glabrous or strigillose; primary branches 5-25 cm, remote, stiffly ascending to divaricate, with axillary pulvini, usually naked near the base; secondary branches and pedicels usually appressed. Spikelets usually congested. Glumes subequal, 9-15 mm, 1-veined, acuminate; calluses 1-1.2 mm; lemmas 9-15 mm long, smooth to tuberculate-scabrous, narrowing to slightly keeled, usually not twisted, 0.1-0.2 mm wide apices, junction with the awns not evident; awns unequal or almost equal, not disarticulating at maturity; central awns 8-25(30) mm, straight to arcuate at the base; lateral awns absent or to 0-23 mm; anthers 3, 1.2-2.4 mm. Caryopses 6-8 mm, light brownish. 2n = 22, 24.

Aristida ternipes var. gentilis (Henrard) Allred
Hook Threeawn

Awns subequal to unequal, ascending to spreading; central awns 10-25(30) mm; lateral awns (2)6-23 mm. 2n = 44.

Aristida ternipes var. gentilis grows on dry slopes and plains and along roadsides from Californica to Texas and south through Mexico to Guatemala.

Aristida ternipes Cav. var. ternipes
Spidergrass

Awns markedly unequal; central awns 8-25 mm, straight to curving; lateral awns absent or to 2 mm, erect. 2n = 22, 44.

Aristida ternipes var. ternipes, like var. gentilis, grows on dry slopes and plains and along roadsides, but its range is somewhat different, extending from Arizona to Texas south through Mexico and Central America to South America.

7.   Aristida schiedeana Trin. & Rupr.
Single Threeawn

Plants perennial; cespitose. Culms 30-120 cm, erect, unbranched. Leaves basal and cauline, pale green, sometimes glaucous; sheaths longer or shorter than the internodes, glabrous except at the summit; collars densely to sparsely pilose or glabrous; ligules less than 0.5 mm; blades 8-30 cm long, 1-2 mm wide, usually flat, often curled at maturity. Inflorescences paniculate, 10-30 cm long, (4)8-26 cm wide; rachis nodes with straight hairs, hairs to 0.8 mm; primary branches 6-16 cm, abruptly spreading to divaricate, stiff to lax, with axillary pulvini, usually not spikelet-bearing below midlength. Spikelets appressed, rarely spreading. Glumes 1(3)-veined, brown or purple at maturity, acuminate; lower glumes 6-13 mm; upper glumes equaling or to 4 mm shorter than the lower glumes; calluses 0.8-1.2 mm; lemmas 10-15(17) mm, terminating in a strongly twisted, 2-4 mm awnlike beak, junction with the awns not conspicuous; awns not disarticulating at maturity; central awns 5-12 mm, markedly bent near the base; lateral awns absent or to 1(3) mm, erect; anthers 1.2-2.2 mm, brownish. Caryopses 6-8 mm. 2n = 22, 44.

Aristida schiedeana grows on rocky slopes and plains, generally in pinyon-juniper, oak, or ponderosa pine communities. Plants from the southwestern United States and northern Mexico belong to Aristida scheideana var. orcuttiana (Vasey) Allred & Valdés-Reyna, in which the lower glumes are usually glabrous and longer than the upper glumes, and the collar and throat are usually glabrous. Aristida schiedeana Trin. & Rupr. var. schiedeana grows in Mexico, Guatemala, Nicaragua, and Honduras, and has puberulent, equal glumes and pilose collars and throats.

8.   Aristida divaricata Humb. & Bonpl. ex Willd.

Plants perennial; cespitose. Culms 25-70 cm, erect or prostrate, unbranched or sparingly branched. Leaves tending to be basal; sheaths longer than the internodes, glabrous except at the summit; collars densely pilose; ligules 0.5-1 mm; blades 5-20 cm long, 1-2 mm wide, flat to loosely involute, glabrous. Inflorescences paniculate, 10-30 cm long, 6-25 cm wide, peduncles flattened and easily broken; rachis nodes glabrous or with hairs, hairs to 0.5 mm; primary branches 5-13 cm, stiffly divaricate to reflexed, with axillary pulvini, usually naked on the basal 1/2; secondary branches usually well-developed. Spikelets overlapping, usually appressed, sometimes divergent and the pedicels with axillary pulvini. Glumes 8-12 mm, 1-veined, acuminate or shortly awned, awns to 4 mm; calluses about 0.5 mm; lemmas 8-13 mm long, the terminal 2-3 mm with 4 or more twists when mature, narrowing to 0.1-0.2 mm wide just below the awns, junction with the awns not evident; awns (7)10-20 mm, not disarticulating at maturity; central awns almost straight to curved at the base, ascending to somewhat divergent distally; lateral awns slightly thinner and from much to slightly shorter than the central awns, ascending to divergent; anthers 3, 0.8-1 mm. Caryopses 8-10 mm, light brown. 2n = 22.

Aristida divaricata grows on dry hills andplains, especially in pinyon-juniper-grassland zones, from the southwestern United States through Mexico to Guatemala. It occasionally intergrades with A. havardii, but that species has lemma beaks that are straight or have only 1-2 twists, shorter primary branches, usually no secondary branches, and pedicels that more frequently have axillary pulvini so the spikelets are more frequently divergent than in A. divaricata.

9.   Aristida havardii Vasey
Havard's Threeawn

Plants perennial; cespitose. Culms 15-40 cm, slender, usually erect, occasionally decumbent, often tightly clustered into hemispheric clumps, unbranched. Leaves mostly basal; sheaths longer than the internodes, glabrous except at the summit; collars densely pilose; ligules 0.5-1 mm; blades 5-20 cm long, 1-2 mm wide, flat to loosely involute, glabrous. Inflorescences paniculate, 8-18 cm long, 4-12 cm wide, peduncles often flattened and easily broken; rachis nodes glabrous or with straight, less than 0.3 mm hairs; primary branches 2-6 cm, stiffly divaricate to reflexed, with axillary pulvini, usually naked on the lower 1/2; secondary branches usually absent. Spikelets usually divergent, pedicels usually with axillary pulvini. Glumes 8-12 mm, 1-veined, acuminate or awned, awns to 4 mm; calluses about 0.5 mm; lemmas 8-13 mm long, glabrous, smooth or scabrous, terminal 2-3 mm straight or with 1-2 twists, narrowing to 0.1-0.2 mm wide, junction with the awns not evident; awns (7)10-22 mm, not disarticulating at maturity, from almost straight to somewhat curved basally, ascending to divergent distally; lateral awns slightly shorter and thinner than the central awns; anthers 3, 0.8-1 mm. Caryopses 8-10 mm, light brown. 2n = 22.

Aristida havardii grows on dry hills and plains in desert grassland to pinyon-juniper zones, and in sandy to rocky ground from the southwestern United States to northern Mexico. It occasionally intergrades with A. divaricata, but that species differs in having more twisted lemma beaks, longer primary branches, well-developed secondary branches, and, usually, appressed spikelets.

10.   Aristida pansa Wooton & Standl.
Wooton's Threeawn

Plants perennial; cespitose. Culms 20-60(75) cm, erect, unbranched. Leaves basal and cauline; sheaths usually longer than the internodes, glabrous except at the summit; collars densely pilose, hairs 1-3 mm, cobwebby and tangled, often deflexed; ligules less than 0.5 mm; blades 4-28 cm long, less than 1 mm wide, usually involute, infrequently flat, usually arcuate, abaxial surfaces glabrous, adaxial surfaces glabrous or puberulent near the base, scabrous or puberulent distally. Inflorescences paniculate, 10-20 cm long, 3-10(12) cm wide; rachis nodes usually glabrous, sometimes with straight, less than 0.3 mm hairs; primary branches 2-11 cm, stiffly ascending to spreading, with axillary pulvini; secondary branches and pedicels with or without pulvini; terminal spikelets often divergent. Spikelets clustered on the distal 1/2 of the branches. Glumes equal or subequal, 1-veined, acuminate or awned, awns to 6 mm, brownish; lower glumes 5-10 mm; upper glumes 6-12 mm; calluses 0.5-1 mm; lemmas 7-13 mm, terminating in an obscure, narrow beak 1-4 mm long, 0.1-0.2 mm wide, junction with the base of the awns not evident; awns 6-15 mm, not disarticulating at maturity, central and lateral awns similar in length and thickness, spreading to horizontal; anthers 3, 1-3 mm, brown. Caryopses 6-8 mm, tan. 2n = unknown.

Aristida pansa grows in desert scrub, commonly in the Chihuahuan desert of the southwestern United States and Mexico, but its ecological range extends into the lower juniper zones and its geographic range to southern Mexico. It prefers cobbly to sandy, often gypsiferous soil. It is very similar to the single-awned A. gypsophila, but it has also been confused with A. purpurea var. perplexa, which differs in having reddish glumes of unequal length and longer ascending awns.

11.   Aristida gypsophila Beetle
Gypsum Threeawn

Plants perennial. Culms 45-80 cm, erect, usually unbranched. Leaves basal and cauline; sheaths longer than the internodes, glabrous except at the summit; collars densely pilose, hairs 1-3 mm, cobwebby and tangled, often deflexed; ligules less than 0.5 mm; blades 5-15 cm long, about 0.5 mm wide, usually involute, occasionally loosely folded, glabrous, light green. Inflorescences paniculate, 12-20 cm long, 2-8 cm wide; primary branches 2-5 cm, erect to horizontal, with or without axillary pulvini, with 1-5 spikelets. Spikelets appressed or with axillary pulvini and spreading. Glumes 6-10(12) mm, equal or the lower glumes slightly shorter, 1-veined, brownish; calluses about 0.5 mm; lemmas (6)7-14(16) mm, mostly smooth, mottled, terminating in a 2-4 mm, usually twisted, scabrous beak; central awns 5-10 mm, sharply curved at the base, spreading distally; lateral awns absent or to 3 mm, erect; anthers 3, about 1.5 mm, brown. Caryopses 5-8 mm. 2n = unknown.

Aristida gypsophila grows on rocky limestone or gypsum hills in thorn-scrub communities of the Chihuahuan desert, almost always growing in the protection of shrubs. It is very similar to A. pansa, which differs in having three well-developed awns and being, usually, shorter in stature. Both species have involute blades with a characteristic tuft of cobwebby hairs at the collar. Plants from the United States have spreading primary branches with axillary pulvini and appressed spikelets. Mexican plants sometimes have primary branches with no axillary pulvini.

12.   Aristida ramosissima Engelm. ex A. Grey
S-Curve Threeawn

Plants annual. Culms 20-60 cm, wiry. Leaves cauline; sheaths usually shorter than the internodes, mostly glabrous, sparsely hairy near the summit; collars hispidulous, occasionally glabrous; ligules 0.2-0.5 mm; blades 3-22 cm long, to 2 mm wide, flat to involute, glabrous abaxially, sparsely pilose adaxially, without a prominent midrib but with a thickened vein near each margin, pale to gray-green, sometimes slightly glaucous. Inflorescences paniculate or racemose, 5-12 cm long, 2-4 cm wide; primary branches barely developed. Spikelets appressed to slightly divergent from the axillary pulvini. Glumes subequal, apices bifid, awned from the sinuses; lower glumes (9)11-16 mm, 3-7-veined, awns 0.5-2(4) mm; upper glumes 11-18 mm, 1-3-veined, awns 3-7 mm; calluses 0.4-1 mm; lemmas (8)15-20(22) mm, dark, occasionally banded or spotted, apices narrowed but not beaklike; central awns 12-25 mm, bases with a semicircular bend; lateral awns 1-4 mm, erect, occasionally lacking; anthers 3, about 3 mm, brown. Caryopses 9-11 mm, dark brown to black. 2n = unknown.

Aristida ramosissima grows in open, dry, sterile ground, fallow fields, and roadsides. It is restricted to the United States.

13.   Aristida oligantha Michx.
Oldfield Threeawn

Plants annual. Culm 25-55 cm, erect or geniculate at the base, highly branched. Leaves cauline; sheaths usually shorter than the internodes, lowermost sheaths appressed-pilose basally; collars glabrous; ligules less than 0.5 mm; blades usually 4-12 cm long, 0.5-1.5 mm wide, flat or loosely involute, somewhat lax, glabrous or scabridulous, pale green. Inflorescences spicate or racemose, (5)7-20 cm long, 2-4 cm wide; primary branches rarely developed. Spikelets divergent, pedicels with axillary pulvini. Glumes unequal, glabrous, brownish-green with a purple tinge; lower glumes (9)12-22(28) mm, 3-7-veined, midvein extended into a 1-13 mm awn between 2 delicate setae; upper glumes (7)11-20(24) mm, 1-veined; calluses 0.5-2 mm; lemmas (9)12-22(23) mm, glabrous, light-colored, often mottled; awns subequal, (8)12-65(70) mm, spreading; anthers usually 1 and less than 0.5 mm, rarely 3 and 3-4 mm. Caryopses 8-14 mm, brown. 2n = 22.

Aristida oligantha grows in waste places, dry fields, roadsides, along railroads, and in burned areas, usually in sandy soil. It has been reported from Coahuila, Mexico, but is otherwise unknown outside southern Canada and the United States.

14.   Aristida basiramea Engelm. ex Vasey
Forktip Threeawn, Aristide à Rameaux Basilaires

Plants annual. Culms 25-45 cm, erect, branching at most nodes. Leaves cauline; sheaths shorter than the internodes, glabrous or sparsely pilose; ligules about 0.3 mm; blades 3-8 cm long, 1-1.5 mm wide, flat to folded, becoming involute in age, adaxial surfaces with scattered pilose hairs, pale green. Inflorescences racemose or paniculate, (2)4-10 cm long, 1-2 cm wide, with few (sometimes only 1 or 2) spikelets; primary branches weakly developed, to 2 cm, appressed, with 1-3 spikelets. Spikelets appressed, only slightly overlapping. Glumes 1-veined, acute, awned, awns 1-2 mm, brown to purplish; upper glumes 10-12 mm; lower glumes 1-2 mm shorter; calluses 0.4-0.6 mm; lemmas 8-9 mm, light gray, mottled; awns erect to divergent; central awns 10-15 mm, with 2-3 spiral coils at the base; lateral awns 5-10 mm, not coiled but often curved and twisted basally, strongly divergent distally; anthers 3, about 3 mm, purplish-brown. Caryopses 6-7 mm, light chestnut brown. 2n = unknown.

Aristida basiramea grows in open, sandy, often barren ground in southern Ontario and in the United States. It is similar to A. dichotoma, differing in its longer lateral awns. Further study may show that the two should be treated as conspecific varieties.

15.   Aristida dichotoma Michx.
Churchmouse Threeawn

Plants annual. Culms 15-60 cm, erect or geniculate at the base, branching at most of the nodes. Leaves cauline; sheaths usually shorter than the internodes, glabrous or sparsely pilose; collars glabrous; ligules less than 0.5 mm; blades 3-10 cm long, 1-2 mm wide, flat to folded basally, involute distally, scabridulous on both surfaces, occasionally sparsely pilose adaxially, light green. Inflorescences paniculate or racemose, 2-11 cm long, to 1 cm wide; nodes glabrous or strigillose; primary branches 1-2 cm, appressed, without axillary pulvini, with 1-2 spikelets. Spikelets partly overlapping, often in pairs, 1 spikelet subsessile, the other pedicellate. Glumes 1-veined, light gray to dark purplish or brownish; lower glumes 3-8(10) mm, from 1/2 as long as the upper glumes to nearly equaling them; upper glumes 4-13 mm; calluses 0.3-0.5 mm; lemmas 3-11 mm, light gray to purplish, frequently mottled, midveins scabrous, elsewhere glabrous, scabridulous, or sparsely appressed-puberulent, junction with the awns not evident; central awns 3-8 mm, coiled at the base, spreading distally; lateral awns 1-4 mm, straight, erect; anthers 3 and 2-3 mm, or 1 and about 0.25 mm. Caryopses light brown. 2n = unknown.

Aristida dichotoma grows in sandy fields and clearings, disturbed sites and sterile ground, pine woods, and on granitic outcrops of the United States and southern Ontario. The two varieties have similar ecological preferences and extensive overlap in their ranges, but var. curtissii is somewhat more western in its distribution.

Aristida dichotoma is similar to A. basiramea, differing in its shorter lateral awns. Further study may show that the two should be treated as conspecific varieties.

Aristida dichotoma var. curtissii A. Gray

Glumes unequal; lower glumes 5-8(10) mm; upper glumes 7-13 mm; lemmas 6-11 mm, glabrous or scabridulous; central awns 4-8 mm; lateral awns 2-4 mm. Caryopses 4-9 mm.

Aristida dichotoma Michx. var. dichotoma

Glumes equal or subequal; lower glumes 3-6 mm; upper glumes 4-7 mm; lemmas 3-8 mm, sparsely appressed-pubescent; central awns 3-6 mm; lateral awns about 1 mm. Caryopses 2-6 mm.

16.   Aristida longespica Poir.

Plants annual. Culms 15-65 cm, erect to spreading, often geniculate-based, sometimes nearly prostrate, usually much-branched. Leaves cauline; sheaths shorter than the internodes, not disintegrating into threadlike fibers at maturity, glabrous or sparsely pilose, hairs on the throat sometimes to 5 mm; collars glabrous; ligules about 0.5 mm; blades 5-14 cm long, 1-2 mm wide, flat to loosely involute, light green. Inflorescences usually paniculate, occasionally racemose or spicate, 6-22 cm long, 1-4(6) cm wide; nodes glabrous or with straight hairs, hairs to 0.3 mm; primary branches 1-4 cm, appressed to erect, rarely somewhat spreading distally, without axillary pulvini, with 2-5 spikelets per branch. Spikelets widely spaced to crowded. Glumes subequal, 2-11 mm, 1-veined, acuminate, unawned or awned, awns to 1 mm; calluses less than 1 mm; lemmas 2.5-10 mm, gray to dark purplish-brown, often horizontally banded or mottled, scabrous-hispid or glabrous, not beaked, apices only slightly narrowed, junction with the awns not evident; awns usually unequal, terete and curving up to 100° atthe base, erect to reflexed distally, not disarticulating at maturity; central awns 1-27 mm; lateral awns absent or to 18 mm, shorter than the central awns; anthers 1 and 0.2-0.3 mm, or 3 and 3-4 mm. Caryopses 3-4 mm, light brown. 2n = unknown.

Aristida longespica grows along roadsides and in waste places, sandy fields, and clearings in pine and oak woods of southern Ontario and the eastern and central United States. The two varieties have a similar geographic range and are often found growing together.

Aristida longespica var. geniculata (Raf.) Fernald
Kearney's Threeawn

Glumes 4-11 mm; lemmas 3.5-10 mm; central awns (8)12-27 mm, erect to reflexed; lateral awns (1)6-18 mm, erect to horizontal; anthers 1 or 3.

Aristida longespica Poir. var. longespica
Slimspike Threeawn

Glumes 2-8 mm; lemmas 2.5-7 mm; central awns 1-10(14) mm, erect to reflexed; lateral awns absent or to 5(8) mm, erect to ascending; anthers 1, rarely exserted.

17.   Aristida adscensionis L.
Sixweeks Threeawn

Plants short- to long-lived annuals. Culms (3)10-50(80) cm, often highly branched above the base. Leaves cauline, glabrous; sheaths shorter than the internodes, not disintegrating into threadlike fibers; ligules 0.4-1 mm; blades 2-14 cm long, 1-2.5 mm wide, flat to involute. Inflorescences panicles, 5-15(20) cm long, 0.5-3 cm wide, often interrupted below; nodes glabrous or with straight, less than 0.5 mm hairs; primary branches 1-4 cm, erect to ascending, without axillary pulvini, with 3-8 spikelets. Spikelets crowded. Glumes unequal, 1-veined, acuminate; lower glumes 4-8 mm; upper glumes 6-11 mm; calluses 0.5-0.8 mm; lemmas 6-9 mm, slightly keeled, midveins scabrous, junction with the awns not evident; awns not disarticulating at maturity, flattened and straight to somewhat curved at the base, central rib flanked by equally wide pale wings; central awns 7-15(20) mm; lateral awns somewhat shorter, occasionally only 1-2 mm; anthers 3, 0.3-0.7 mm. 2n = 22.

Aristida adscensionis grows in waste ground, along roadsides, and on degraded rangelands and dry hillsides, often in sandy soils. It is associated with woodland, prairie, and desert shrub communities. Its range extends from the United States south through Mexico and Central America to South America.

Because A. adscensionis is highly variable in height, panicle size, and awn development, several varieties have been described. None are recognized here because most of the variation appears to be environmentally induced.

18.   Aristida spiciformis Elliott
Bottlebrush Threeawn

Plants perennial; cespitose. Culms 45-100 cm, unbranched or sparingly branched. Leaves cauline; sheaths shorter than the internodes, glabrous except for occasional hairs at the summit; collars glabrous, or with a few pilose hairs at the sides; ligules about 0.5 mm; blades 12-28 cm long, 1-3 mm wide, usually folded or loosely involute, light yellow-green, glabrous abaxially, puberulent adaxially. Inflorescences dense panicles, (3)8-24 cm long, 2-4 cm wide, somewhat spirally twisted in age; nodes glabrous or strigillose, hairs about 0.1 mm; primary branches 2-4 cm, tightly appressed, without axillary pulvini, with 6-10 spikelets per branch. Glumes lanceolate, 1-veined; lower glumes 3.5-4.5 mm, abruptly contracted to a 4-12 mm awn; upper glumes 7-10 mm, gradually narrowed to a 10-12 mm awn; calluses about 2 mm; lemmas 5-6 mm, dark brown or purplish, terminating in a straight or twisted beak 7-30 mm long, about 0.2 mm wide, beak often disarticulating, no obvious zone of articulation developed, junction of the beak and awns sometimes evident; awns usually unequal, strongly curved and twisted at the base, straight distally, sometimes disarticulating at maturity; central awns (10)20-30 mm; lateral awns 10-20(25) mm, at least 1/2 as long as and evidently thinner than the central awns; anthers 3, about 1 mm, brown. Caryopses 4-5 mm, including the delicate style column. 2n = unknown.

Aristida spiciformis grows in pine savannahs, pine flatwoods, pine-oak sandhills, and oak woods, frequently being associated with Pinus palustris. It is a primary fire carrier in these habitats. Its range includes Cuba and Puerto Rico as well as the southeastern United States.

19.   Aristida purpurea Nutt.

Plants perennial; densely cespitose, without rhizomes. Culms 10-100 cm, erect to ascending, usually unbranched. Leaves mostly basal or mostly cauline; sheaths shorter or longer than the internodes, glabrous, not disintegrating into threadlike fibers at maturity; collars glabrous, or sparsely pilose at the sides with straight hairs; ligules less than 0.5 mm; blades 4-25 cm long, 1-1.5 mm wide, tightly involute to flat, usually glabrous, sometimes scabridulous abaxially, gray-green, lax to curled at maturity. Inflorescences usually sparingly branched panicles, occasionally racemes, 3-30 cm long, 2-12 cm wide, with 2 or more spikelets per node; nodes glabrous or with straight, about 0.5 mm hairs; primary branches 3-6 cm, appressed to divaricate, varying sometimes within a panicle, stiff to flexible, bases appressed or abruptly spreading, usually without axillary pulvini. Spikelets divergent or appressed, with or without axillary pulvini. Glumes usually unequal, lower glumes shorter than the upper glumes, sometimes subequal, light to dark brown or purplish, glabrous, smooth or scabridulous, 1(2)-veined, acuminate, unawned or awned, awns to 1 mm; lower glumes 4-12 mm; upper glumes 7-25 mm; calluses 0.5-1.8 mm; lemmas 6-16 mm, glabrous, scabridulous, or tuberculate, whitish to purplish, apices 0.1-0.8 mm wide, not beaked or the beak less than 3 mm, junction with the awns not conspicuous; awns (8)13-140 mm, ascending to divaricate, not disarticulating at maturity; central awns thicker than the lateral awns; lateral awns (8)13-140 mm, usually subequal to the central awns, occasionally less than 1/3 as long as the central awns; anthers 3, 0.7-2 mm. Caryopses 6-14 mm, tan to chestnut. 2n = 22, 44, 66, 88.

Aristida purpurea is composed of several intergrading varieties.

Aristida purpurea var. fendleriana (Steud.) Vasey
Fendler's Threeawn

Culms 10-40 cm. Leaves mostly cauline; blades 4-10 cm, involute. Panicles 3-14(15) cm; primary branches mostly appressed, stiff, straight, without axillary pulvini, with few spikelets. Lower glumes 5-8 mm; upper glumes 10-15 mm; lemmas 8-14 mm long, apices 0.2-0.3 wide; awns subequal, 18-40 mm long, occasionally slightly longer, 0.2-0.3 mm wide at the base. 2n = 22, 44.

Aristida purpurea var. fendleriana grows on open slopes, hills, and sandy flats, at low to medium elevations, from the western United States into northern Mexico. It is often confused with var. longiseta, having short basal leaves and short panicles, but plants of var. fendleriana have narrower lemma apices and thinner, shorter awns than those of var. longiseta.

Aristida purpurea var. longiseta (Steud.) Vasey
Red Threeawn

Culms 10-40(50) cm. Leaves sometimes mostly basal, sometimes mostly cauline; blades 4-16 cm, usually involute. Panicles 5-15 cm; primary branches appressed or ascending at the base, without axillary pulvini, stout andstraight to delicate and drooping distally, usually neither flexible nor tangled. Lower glumes 8-12 mm; upper glumes (14)16-25 mm; lemmas 12-16 mm long, apices 0.3-0.8 mm wide; awns subequal, 40-100(140) mm long, 0.2-0.5 mm wide at the base. 2n = 22, 44, 66, 88.

Aristida purpurea var. longiseta grows on sandy or rocky slopes and plains, and in barren soils of disturbed ground from western Canada to northern Mexico. It is the most variable variety of Aristida purpurea, ranging from short plants with basal leaves and short panicles suggestive of var. fendleriana, to tall plants with long cauline leaves and long, drooping panicles resembling var. purpurea. The length of its glumes, width of its lemma apex, and the length and thickness of its awns distinguish it from all the other varieties. The callus and long, stiff awns are especially troublesome to sheep and cattle.

Aristida purpurea var. nealleyi (Vasey) Allred
Nealley's Threeawn

Culms 20-45 cm. Blades 5-15 cm, mostly basal, involute. Panicles 8-18(20) cm; primary branches and pedicels mostly appressed to narrowly ascending, without axillary pulvini, stiff, straight, lower branches occasionally flexible. Glumes usually unequal; lower glumes 4-7 mm; upper glumes (7)8-14 mm; lemmas 7-13 mm long, narrowing to about 0.1 mm wide, upper portion sometimes twisted; awns subequal, 15-22(30) mm long, about 0.1 mm wide at the base. 2n = 22, 44.

Aristida purpurea var. nealleyi grows on dry slopes and plains at lower elevations than the other varieties, frequently in desert grassland vegetation. Its range extends from the southwestern United States into Mexico. Although var. nealleyi is more distinct than the other varieties, having tight tufts of foliage exceeded by narrow, straw-colored panicles, it grades into var. purpurea, and the panicles resemble those of var. wrightii. It may also be confused with A. arizonica, but differs in having involute, generally straight leaf blades and shorter awns.

Aristida purpurea var. parishii (Hitchc.) Allred
Parish's Threeawn

Culms 20-50 cm. Leaves mostly cauline; blades more than 10 cm, loosely involute to flat. Panicles 15-24 cm; primary branches stiff, lower branches strongly divergent to divaricate, with axillary pulvini, upper branches appressed to ascending, without axillary pulvini, lower nodes associated with 8-18 spikelets. Glumes red or dark at anthesis, fading to stramineous; lower glumes 7-11 mm, 3/4 as long as to equaling the upper glumes; upper glumes 10-15 mm; lemmas 10-13 mm long, narrowing to 0.2-0.3 mm wide near the apex; awns subequal, 20-30 mm long, 0.2-0.3 mm wide at the base. 2n = unknown.

Aristida purpurea var. parishii grows on sandy plains and hills of the southwestern United States and Baja California, Mexico. In many respects it is intermediate between A. purpurea and other species of Aristida with spreading panicle branches, especially A. ternipes var. gentilis. Its spikelets are indistinguishable from those of var. wrightii, but var. parishii frequently has axillary pulvini associated with the lower branches. The two also differ in their phenology: var. parishii flowers from March through May in response to winter rains, whereas var. wrightii flowers from May through October in response to summer rains.

Aristida purpurea var. perplexa Allred & Valdés-Reyna
Jornada Threeawn

Culms 30-65 cm. Blades 8-20 cm, involute. Panicles 8-20 cm; primary branches stiff, lower branches diverging or divaricate, with axillary pulvini, upper branches usually strongly divergent, sometimes ascending; pedicels often with axillary pulvini; terminal spikelets usually appressed. Glumes reddish; lower glumes (4.5)5-7(7.5) mm, 1/2-2/3 as long as the upper glumes; upper glumes 8-11(12) mm; lemmas (8)10-12(13) mm long, narrowing to 0.1-0.2 mm wide; awns subequal, (13)18-30 mm long, 0.1-0.2 mm wide. 2n = unknown.

Aristida purpurea var. perplexa grows in sandy to rocky plains and on mesas in desert grassland and scrub communities, often in calcareous soils, in both the Flora region and Mexico. It is sometimes confused with A. pansa, which differs in having cobwebby hairs at the collar, equal glumes, and shorter awns.

Aristida purpurea Nutt. var. purpurea
Purple Threeawn

Culms 26-60 cm. Blades 3-17 cm, basal and cauline, involute. Panicles 10-25 cm; primary branches appressed at the base, without axillary pulvini, capillary, drooping to sinuous distally; pedicels capillary, usually lax to sinuous. Lower glumes 4-9 mm; upper glumes 7-16 mm; lemmas 6-12 mm long, narrowing to 0.1-0.3 mm wide; awns subequal, (15)20-60 mm long, 0.1-0.3 mm wide at the base. 2n = 22, 44, 66, 88.

Aristida purpurea var. purpurea grows in sandy to clay soils, along right of ways, or on dry slopes and mesas. Its range extends from the Flora region to Mexico and Cuba. As treated here, var. purpurea is, admittedly, a catch-all taxon, incorporating slender plants with small spikelets that used to be referred to A. roemeriana Scheele, but also occasional plants with somewhat flexible branches that are intermediate to var. wrightii and var. nealleyi.

Aristida purpurea var. wrightii (Nash) Allred
Wright's Threeawn

Culms 45-100 cm. Blades 10-25 cm, involute or flat. Panicles (12)14-30 cm; primary branches usually erect, without axillary pulvini, stiff, straight, lower nodes associated with 2-10 spikelets. Glumes tan to brown, fading to stramineous. Lower glumes 5-10 mm; upper glumes 9-16 mm; lemmas 8-14 mm long, narrowing to 0.2-0.3 mm wide; awns (8)20-35 mm long, 0.2-0.3 mm wide at the base, lateral awns usually subequal to the central awn, rarely 1-3 mm. 2n = 22, 44, 66.

Aristida purpurea var. wrightii grows on sandy to gravelly hills and flats from the southwestern United States to southern Mexico. It is the most robust variety of A. purpurea, and has dark, stout awns and long panicles. It may be confused with var. nealleyi, which has narrower lemmas and awns and a light-colored panicle, but it also intergrades with var. purpurea and var. parishii. Aristida purpurea forma brownii (Warnock) Allred & Valdés-Reyna refers to plants with short central awns and lateral awns that are only 1-3 mm long.

20.   Aristida arizonica Vasey
Arizona Threeawn

Plants perennial; usually cespitose, occasionally with rhizomes. Culms 30-80(100) cm, erect, unbranched. Leaves mostly basal; sheaths usually longer than the internodes, mostly glabrous, throat sometimes with hairs, not disintegrating into threadlike fibers; collars glabrous or with hairs at the sides; ligules 0.2-0.4 mm; blades 10-25(30) cm long, 1-3 mm wide, usually flat, often curling like wood shavings when mature, glabrous. Inflorescences spikelike panicles, 10-25 cm long, 1-3 cm wide; nodes glabrous or with straight, about 0.5 mm hairs; primary branches 2-6 cm, appressed, without axillary pulvini, with 2-8 spikelets. Glumes 10-15(18) mm, brownish, acuminate to awned, awns to 3 mm; lower glumes slightly shorter than to equaling the upper glumes, 1-2-veined; calluses 1-1.8 mm; lemmas 12-18 mm, glabrous, rarely sparsely pilose, terminating in a 3-6 mm twisted column, junction with the awns not conspicuous; awns 20-35 mm, straight to curved basally, ascending distally, not disarticulating at maturity; central awns 20-35 mm; lateral awns slightly shorter than the central awns; anthers 3, 1.3-1.9 mm. 2n = 22.

Aristida arizonica grows in pine, pine-oak, and pinyon-juniper woodlands from the southwestern United States to southern Mexico. It may be confused with A. purpurea var. nealleyi, but differs in having flat, curly leaf blades and longer awns.

21.   Aristida stricta Michx.
Wiregrass, Pineland Threeawn

Plants perennial; cespitose, occasionally with rhizomes. Culms 60-120 cm, stiffly erect, unbranched. Leaves basal or nearly basal; sheaths shorter than the internodes, smooth and mostly glabrous abaxially, sometimes with a line of widely spaced, 0.5-1 mm hairs over the midvein, not disintegrating into threadlike fibers at maturity; collars glabrous, sometimes with a few conspicuous hairs at the sides; ligules 0.1-0.3 mm; blades 15-50 cm long, 0.3-1 mm wide, tightly involute, stiff, yellow-green, abaxial surfaces villous on both sides of the midvein, at least on the basal portion, hairs 0.6-1.5 mm, adaxial surfaces densely scabrous or densely short pubescent. Inflorescences paniculate, 20-35 cm, 5-8 mm wide; nodes glabrous; primary branches 2-5 cm, appressed, without axillary pulvini, with 4-12 spikelets, spikelet-bearing to the base. Spikelets appressed. Glumes subequal, glabrous, light brown or tan, usually 1(2)-veined, bifid and awned, awns 1.5-2.5 mm; lower glumes 7-10 mm; upper glumes 6-9 mm; calluses 0.4-0.6 mm; lemmas 6-9 mm, glabrous, light-colored when young, reddish when mature, column 1-2 mm, not twisted, junction with the awns inconspicuous; awns subequal, (7)10-15(22) mm, usually horizontally spreading or curving downward, not disarticulating at maturity; anthers 3, about 3 mm, reddish-brown. Caryopses 4-5 mm, chestnut brown. 2n = unknown.

Aristida stricta grows in pine barrens and sandy fields of the coastal plain from Lousiana to North Carolina. Peet (1993) segregated northern populations of Aristida stricta as a separate species, A. beyrichiana Trin. & Rupr., based on pubescence patterns of the sheath and blades. Investigations into alloyzyme diversity (Walters et al. 1994), anatomy, morphology, and phenotypic expression (garden transplants) led Kesler (2000) to conclude that such a segregation was not justified; pubescence patterns particularly were inconclusive. Consequently, A. beyrichiana is treated here as part of A. stricta.

22.   Aristida rhizomophora Swallen

Plants perennial; cespitose, with well-developed, thick, dark rhizomes. Culms 60-100 cm, erect, unbranched. Leaves mostly basal; sheaths longer than the internodes, glabrous, basal sheaths many-veined, shredding into threadlike segments at maturity; collars glabrous or sparsely pilose at the corners; ligules 0.1-0.2 mm; blades 10-55 cm long, 1-3 mm wide, flat to folded, glabrous, pale green to yellow-green, central veins separate and narrow, without a well-defined midrib, lateral veins forming a thickened region on each margin. Inflorescences paniculate, (10)20-45 cm long, 2-6 cm wide; nodes glabrous; primary branches (2)4-15 cm, basal branches appressed, without axillary pulvini, distal branches ascending, occasionally lax or drooping distally. Spikelets appressed. Glumes unequal, brown to chestnut, 1-veined, awned; lower glumes 6-12 mm, awns 2-5 mm; upper glumes 13-18 mm, awns 3-6 mm; calluses 0.4-0.8 mm; lemmas 9-13 mm long, narrowing to a poorly defined beak 1-2 mm long and 0.2-0.3 mm wide, glabrous, tan to brown, junction with the awns not conspicuous; awns usually unequal, not disarticulating at maturity; central awns 15-30 mm, curved to semicircular at the base, horizontal to reflexed distally; lateral awns 13-20 mm, at least 1/2 as long as the central awns, curved or loosely twisted at the base, straight and strongly divergent distally; anthers 3, about 4 mm, yellow. Caryopses 6-8 mm, tan to brown. 2n = unknown.

Aristida rhizomophora is not well-collected. It is endemic to Florida, where it grows in moist to wet pine flatwoods, and on the borders of ponds and bald-cypress depressions.

23.   Aristida mohrii Nash
Mohr's Threeawn

Plants perennial; cespitose, bases knotty. Culms 55-110 cm, erect, unbranched. Leaves cauline; sheaths shorter or longer than the internodes, glabrous, not disintegrating at maturity; collars glabrous, or sparsely pilose at the sides; ligules about 0.2 mm; blades 5-25 cm long, 1-2 mm wide, flat or loosely folded, pale green, cauline leaves usually glabrous adaxially, innovation leaves pilose. Inflorescences spikelike racemes, 20-45 cm long, 1-2 cm wide; nodes glabrous, with only 1 spikelet. Spikelets solitary, not overlapping. Glumes 9-11 mm, equal or the lower glumes slightly longer than the upper glumes, narrowly oblong, often slightly falcate, tan to brown, 1-veined; lower glumes occasionally with 1-2 faint lateral veins, awn-tipped, awns about 0.5 mm; upper glume awned, awns 1-2.5 mm; calluses 1-1.5 mm; lemmas 7-10 mm, brown, lead-colored, or purplish, not beaked, junction with the awns not evident; awns equally thick, not disarticulating at maturity; central awns 14-20 mm, slightly longer than the lateral awns, strongly curved basally, distal portion reflexed; lateral awns horizontal to reflexed; anthers 3, about 4.5 mm, purplish. Caryopses 4-5 mm, chestnut-colored. 2n = unknown.

Aristida mohrii is endemic to the southeastern United States, growing on dry, sandy pinelands and oak barrens, and occasionally in waste places. It is sometimes confused with A. simpliciflora because both have reduced, spikelike inflorescences, but A. simpliciflora has lateral awns that are only about half as thick as the central awn, and its spikelets are borne in pairs.

24.   Aristida simpliciflora Chapm.
Southern Threeawn

Plants perennial; loosely cespitose. Culms 30-80 cm, loosely branched below; internodes hollow. Leaves cauline, mostly glabrous; sheaths shorter than the internodes, remaining intact at maturity; ligules about 0.1 mm; blades 5-15 cm long, 0.8-1.5 mm wide, usually flat, those of the innovations often sparsely pilose. Inflorescences narrowly racemose, 10-30 cm long, 1-2 cm wide, often nodding; nodes glabrous; lower pedicels appressed. Spikelets usually 2(1-3) per node, 1 sessile or short-pedicellate and 1 long-pedicellate. Glumes subequal, 6-9 mm, tan to purplish, 1-2-veined, acute to awn-tipped, awns 0.5-1.5 mm; lower glumes frequently 2-keeled; calluses 0.4-0.6 mm; lemmas 5-6 mm, light tan to lead-colored, column not twisted, junction with the awns not conspicuous; awns not disarticulating at maturity; central awns 10-15 mm, about twice as thick as the lateral awns, reflexed from a semicircular bend; lateral awns equal to or slightly shorter than the central awns, divaricate and slightly contorted at the base; anthers 3, 2-3 mm, tan to brown. Caryopses 4-5 mm, chestnut-colored. 2n = unknown.

Aristida simpliciflora grows in wet savannahs, the upper portion of seepage bogs, and the moister portion of ecotones between such bogs and the surrounding dry uplands. It is restricted to the southeastern United States.

Aristida simpliciflora is sometimes confused with A. mohri because both have reduced, spikelike inflorescences, but A. mohri has lateral awns that are about as thick as the central awn, and its spikelets are solitary.

25.   Aristida lanosa Muhl. ex Elliott
Wooly Threeawn

Plants perennial; loosely cespitose. Culms 65-150 cm, sometimes thickened at the base, erect, unbranched; internodes glabrous; nodes concealed. Leaves cauline; sheaths longer than the internodes, usually lanose-floccose, occasionally glabrate; ligules about 0.1 mm; blades 10-25(30) cm long, 2-6 mm wide, flat, light green or slightly blue-green, glabrous abaxially. Inflorescences paniculate, (25)35-70(82) cm long, (2)3-8(10) cm wide; rachis nodes lanose-floccose; primary branches 3-12 cm, appressed at the base, without axillary pulvini, ascending to spreading distally, sometimes loose and somewhat flexible, with 4-12 spikelets per branch. Glumes usually unequal, 1-veined, brownish-green to dark brown or purplish; lower glumes 8.7-18 mm, with a keeled midvein; upper glumes 8.4-15 mm, awn-tipped, awns to 3 mm; calluses 0.5-1 mm; lemmas 6.5-10 mm, smooth to scabridulous, mostly dark purplish-mottled, slightly narrowed distally but not beaked, junction with the awns not evident; central awns 12-28 mm, curved at the base, often strongly so; lateral awns 7-17 mm, at least 1/2 as long as the central awns; anthers 3, about 3 mm, brown. Caryopses 5-6 mm, chestnut brown. 2n = unknown.

Aristida lanosa is restricted to the eastern United States, where it grows in dry fields, pine-oak woods, and uplands, chiefly in sandy soil. It is sometimes confused with A. palustris, but differs in several reproductive, vegetative, and habitat characteristics.

26.   Aristida palustris (Chapm.) Vasey
Longleaf Threeawn

Plants perennial; cespitose, bases hard, knotty. Culms 90-150 cm, often thickened basally, stiffly erect, usually unbranched; internodes hollow. Leaves cauline; sheaths usually shorter than the internodes, glabrous, remaining intact at maturity; collars glabrous; ligules to 0.1 mm; blades (8)10-30(35) cm long, 2-4 mm wide, usually flat, occasionally loosely involute, lax, glabrous, light yellow-green to bluish-green when young, drying brownish. Inflorescences paniculate, 25-45(55) cm long, 3-6 cm wide; nodes glabrous; primary branches 2-8 cm, usually single or paired, appressed to erect, occasionally ascending, without axillary pulvini, with (1)2-12 spikelets. Spikelets overlapping, appressed. Glumes subequal, (7.5)9-13.5 mm, stiff, glabrous or scabridulous, light brown or greenish-brown; lower glumes prominently 2-veined, 2-keeled by the development of 1 lateral vein, shortly (1-2 mm) awn-tipped; upper glumes 1-veined, shortly (0.5-1 mm) awn-tipped; calluses 1-1.4 mm; lemmas 6-9 mm, glabrous, 0.3-0.5 mm wide distally, light tan to brown, junction with the awns not evident; awns not disarticulating at maturity; central awns 15-40 mm, usually strongly curved basally, strongly divergent to horizontal distally; lateral awns 8-35 mm, at least 1/2 as long as the central awns, erect to strongly divergent; anthers 3, about 3 mm, purplish. Caryopses 4.4-5 mm, chestnut brown. 2n = unknown.

Aristida palustris is endemic to the southeastern United States, where it grows in seepage bogs, pitcher plant savannahs, wet pine flatwoods, bald-cypress depressions, and wet prairies. It is a distinctive species of the southeastern coastal plain region that differs from A. lanosa in several reproductive, vegetative, and habitat characteristics.

27.   Aristida purpurascens Poir.

Plants perennial; cespitose, bases knotty, without rhizomes. Culms 40-100 cm tall, 1-4 mm thick at the base, erect, branching at the base, shoots becoming thickened and somewhat fan-shaped upwards. Leaves cauline; sheaths mostly longer than the internode, mostly or completely glabrous, sometimes pilose, particularly along the margins and at the throat, remaining intact at maturity; collars glabrous or pilose; ligules about 0.2 mm; blades 10-25 cm long, 1-3 mm wide, usually flat, usually lax, sometimes sinuous to curling at maturity, glabrous, pale green, drying brownish. Inflorescences paniculate, (15)20-55 cm long, 0.5-2(3) cm wide, often nodding; nodes glabrous, sometimes scabrous, lower nodes usually associated with more than 2 spikelets; primary branches 1-5 cm, tightly appressed to loosely ascending, without axillary pulvini, with 1-8 spikelets. Spikelets appressed. Glumes 5-10 mm, lower glumes from 3/4 as long as to 1-4 mm longer than the upper glumes, glabrous or sparsely appressed-pubescent, 1-2-veined, 1-keeled, tan to purplish, unawned or the awns no longer than 1 mm; calluses 0.4-0.8 mm; lemmas 4-8 mm, glabrous, mostly light tan or gray, often spotted or banded, beak not twisted, junction with the awns not evident; awns 8-25 mm, equal or subequal in length, curved, arcuate, or spirally coiled at the base, not disarticulating at maturity; central awns sometimes thicker than the lateral awns, erect to arcuate-reflexed; lateral awns straight and erect, ascending, or divergent; anthers 1 or 3, 1-1.5 mm, brown. Caryopses 3-5 mm, chestnut brown. 2n = unknown.

Aristida purpurascens is composed of three intergrading varieties, as follows:

Aristida purpurascens Poir. var. purpurascens
Arrowfeather Threeawn, Threeawn

Lower sheaths longer than the internodes, usually glabrous, or occasionally with appressed-pilose hairs; blades 1-3 mm wide, often curling. Glumes unequal; lower glumes 6-10 mm, usually longer than the upper glumes; upper glumes 5-8 mm; awns 15-25 mm, of equal thickness, straight or only slightly contorted, divergent.

Aristida purpurascens var. purpurascens grows in waste places, glades, fields, and pine savannahs in sandy or clay soils. Its range extends into northern Mexico.

Aristida purpurascens var. tenuispica (Hitchc.) Allred

Lower sheaths shorter or longer than the internodes, glabrous; blades usually about 1 mm wide, usually not curling. Glumes subequal, 8-9 mm; awns 12-18 mm, of equal thickness, spirally contorted at the base, divergent.

Aristida purpurascens var. tenuispica grows in pine and oak woods, prairies, and along roadsides, at low elevations and usually in sandy soils. Within the Flora region, it grows on the coastal plain from North Carolina to Mississippi. It also grows in Mexico and Honduras.

Aristida purpurascens var. virgata (Trin.) Allred

Lower sheaths shorter or longer than the internodes, glabrous. Glumes 6-7 mm, equal or the lower glumes slightly longer; central awns 13-20 mm, about twice as thick as the lateral awns, divaricate to reflexed at maturity; lateral awns 8-13 mm, erect to ascending.

Aristida purpurascens var. virgata grows in wet or moist areas such as seepage bogs, sandy pinelands, and wet prairies of the southeastern United States.

28.   Aristida condensata Chapm.
Big Threeawn

Plants perennial; bases knotty, bleached, not rhizomatous. Culms 70-150 cm tall, 3-6 mm thick at the base, erect, rarely branched. Leaves mostly cauline; sheaths usually longer than the internodes, remaining intact at maturity, glabrous or appressed pilose; collars glabrous or pilose at the sides; ligules less than 0.5 mm; blades (10)15-30 cm long, 1.5-3 mm wide, flat at the base, involute toward the apex, straight to somewhat lax at maturity, glabrous abaxially, yellowish-green when fresh, drying stramineous or darker. Inflorescences paniculate, (15)20-55 cm long, 2-4 cm wide; nodes glabrous or with short, straight hairs; primary branches (4)5-20 cm, appressed to narrowly ascending, without axillary pulvini, naked below, with 5-15 overlapping spikelets distally. Glumes 6-10(12) mm, 1-veined, 1-keeled, awns less than 4 mm, brownish; lower glumes from 3/4 as long as to 1 mm longer than the upper glumes; calluses 1-2 mm; lemmas 5-8 mm, often reddish-mottled, apices not strongly twisted, junction with the awns not evident; awns about equally thick, divergent, spirally contorted at the base but usually not with distinct coils, not disarticulating at maturity; central awns 10-15 mm; lateral awns 8-13 mm; anthers 3, about 2 mm. Caryopses 4-5 mm, chestnut-colored. 2n = unknown.

Aristida condensata grows on sandy hills, and in pine and oak barrens in the southeastern United States.

29.   Aristida gyrans Chapm.
Corkscrew Threeawn

Plants perennial; tightly cespitose, bases often bleached, without rhizomes. Culms 20-65 cm tall, 1-4 mm thick at the base, erect, rarely geniculate at the base, unbranched; internodes often in a sequence of 2 short and 1 long. Leaves mostly basal; sheaths usually shorter than the internodes, glabrous, remaining intact at maturity; collars glabrous; ligules 0.2-0.3 mm; blades (3)5-15 cm long, to 1 mm wide, involute, rarely loosely folded or flat, somewhat stiff and arcuate, bases glabrous abaxially, pale green. Inflorescences paniculate or racemose, 10-30 cm long, 1-2 cm wide, slender, lax; primary branches 3-5 cm, loosely appressed, without axillary pulvini, with 2-5 spikelets. Spikelets appressed. Glumes usually unequal, 1-veined, acuminate or awned, awns to 4 mm, tan to dark brownish or purplish; Lower glumes 6-9(11) mm; upper glumes 9-12 mm; calluses 1-2 mm; lemmas 5-7 mm, glabrous, brownish, without a column, the junction with the awns not evident; awns subequal, 8-15 mm, loosely spirally contorted, but not coiled, just above the base, ascending to spreading distally, not disarticulating at maturity; anthers 3, 1-1.5 mm, brownish. Caryopses 3-4 mm, somewhat lustrous, chestnut-colored. 2n = unknown.

Aristida gyrans is endemic to the southeastern United States, growing in sandy pine woods and oak scrub. It differs from other species in the genus by its combination of narrow blades, unequal glumes, long calluses, and contorted awns.