Aristida adscensionis
Aristida gypsophila
sixweeks three-awn, three awn
gypsum threeawn
(3)10-50(80) cm, often highly branched above the base.
45-80 cm, erect, usually unbranched.
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.
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.
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.
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.
crowded.
appressed or with axillary pulvini and spreading.
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.
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.
5-8 mm.
= 22.
= unknown.
Aristida adscensionis
Aristida gypsophila
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 Aristida 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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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