Aristida gypsophila
Aristida pansa
gypsum threeawn
Wooton threeawn, Wooton's threeawn
45-80 cm, erect, usually unbranched.
20-60(75) cm, erect, unbranched.
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.
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.
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.
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.
appressed or with axillary pulvini and spreading.
clustered on the distal 1/2 of the branches.
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.
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.
5-8 mm.
6-8 mm, tan.
= unknown.
= unknown.
Aristida gypsophila
Aristida pansa
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.)
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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