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.
Annual herb 25 cm - 1.2 m tall Leaves: borne along the culm, having open sheaths usually a little shorter than the internodes and hairless or soft-haired with the collars usually having a line of tangled hairs. The ligules are made of hairs about 0.5 mm long, and the blades are light green, 8 - 25 cm long, 2 - 4 mm wide, flat or with margins loosely rolling toward the upper surface of the midvein (involute), hairless beneath, and rough above. Inflorescence: terminal, 10 - 20 cm long, 3 - 10 cm wide, with stiffly ascending primary branches 1 - 4 cm long. Fruit: a dark brown, caryopsis, 8 - 10 mm long, spindle-shaped, with a linear scar. Culm: erect or decumbent to ascending at the base, 25 cm - 1 m tall, highly branched above the base, with hairless nodes and internodes. Spikelets: one to four per branch. Glumes: yellowish brown, 2 - 3 cm long with the upper glumes slightly longer than the lower ones, thin, single-veined, with an awn 5 - 10 mm long. Florets: one per spikelet, with three brownish anthers about 2.5 mm long. Lemma: dark and mottled when mature, 10 - 14 mm long, spindle-shaped and rolled up longitudinally (convolute), three-veined, hairless or sometimes sparsely hairy, with three nearly equal awns. The awns are twisted at the base into a 8 - 15 mm column but remain untwisted and straight at the top 3 - 4 cm. Palea: shorter than the lemma, two-veined.
Similar species: The other species of Aristida that grow in the Chicago Region do not have the distinctive twisted column of awns seen in Aristida tuberculosa.
Flowering: mid August to late September
Habitat and ecology: Dry sandy soil that is fairly open.
Occurence in the Chicago region: native
Etymology: Aristida comes from the Latin word arista, meaning awn. Tuberculosa means "bearing tubercles," which are small tuber-like projections.
Annual 3-8 dm, the culms branched at base and lower nodes; lower sheaths villous, the upper glabrous or nearly so; blades 1-3 mm wide, involute at least when dry; panicle very lax and open, sparsely branched, 1-3 dm; glumes subequal, 20-28 mm, including the short awn, the first scabrous on the keel; lemma 11-14 mm, its awns about equal, united at base into a twisted column 7-13 mm, the free parts loosely coiled at base, about horizontal, 3-5 cm. Dry sterile soil, especially on dunes, along the coast from Mass. to Ga., and inland from Ind. and s. Mich. to Minn. and Io.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.