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.
|Lower or all primary panicle branches stiff, divergent to divaricate from the base, with axillary pulvini; awns 13-30 mm (2)|
Primary panicle branches appressedor ascending at the base, sometimes drooping distally, without axillary pulvini; awns 8-140 mm (3)
Lower glumes 1/2-2/3 as long as the upper glumes ..... var. perplexa
Lower glumes from 3/4 as long as to equaling the upper glumes ..... var. parishii
Awns 35-140 mm long (4)
Awns 8-35 mm long (5)
Lemmas apices 0.1-0.3 mm wide; awns 0.1-0.2(0.3) mm wide at the base, 35-60 mm long; upper glumes usually shorter than 16 mm long ..... var. purpurea
Lemma apices 0.3-0.8 mm wide; awns 0.2-0.5 mm wide at the base, 40-140 cm long; upper glumes 14-25 mm long ..... var. longiseta
Lemma apices 0.1-0.3 mm wide distally; awns 0.1-0.3 mm wide at the base (6)
Lemma apices 0.2-0.3 mm wide; awns stout, 0.2-0.3 mm wide at the base (7)
All or most of the panicle branches straight (lower branches sometimes lax); pedicels straight, appressed to ascending ..... var. nealleyi
All or most of the panicle branches and pedicels drooping to sinuous distally..... var. purpurea
Mature panicle branches and pedicels flexible, lax or drooping distally ..... var. purpurea
Mature panicle branches and pedicels usually stiff, straight (8)
Panicles usually 3-15 cm long; blades 4-10 cm long ..... var. fendleriana
Panicles usually 15-30 cm long; blades 10-25 cm long (9)
Glumes and lemmas reddish or dark-colored at anthesis or earlier (fading to stramineous), usually in marked contrast with the current foliage; panicles dense, the lower nodes with 8-18 spikelets; flowering March to May, after winter rains ..... var. parishii
Glumes and lemmas tan to brown (also fading to stramineous), giving the panicle a brownish appearance; old growth gray-green, not in marked contrast with the current foliage; panicles less dense, the lower nodes with 2-10 spikelets ..... var. wrightii
Aristida purpurea var. fendleriana (Steud.) Vasey
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
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
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
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
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
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
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.
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