1. A. furcàtus, Muhl. ([Pl. 14], fig. 1–3.) Tall, 3–4° high, rigid, the naked summit of the culm (and usually some lateral branches) terminated by 2–5 rigid spikes; spikelets approximate, appressed; hairs at the base of the fertile spikelet, on the rhachis and on the stout pedicel of the awnless staminate spikelet short and rather sparse; awn of fertile flower long and bent; leaves flat, roughish, the lower ones long. ("A. provincialis, Lam.")—Common in dry sterile soil. Aug.–Oct.
[*][*] Spikes with slender often zigzag rhachis, silky-villous.
[+] Single and scattered along the branches, with the silky hairs shorter than the flowers; sterile spikelet conspicuous but mostly neutral; the fertile triandrous.
2. A. scopàrius, Michx. Culms slender (1–3° high), with numerous paniculate branches; lower sheaths and narrow leaves hairy; spikes slender, scattered, mostly peduncled (1–2´ long), very loose, often purplish, silky with lax dull-white hairs; sterile spikelet awn-pointed or awnless; the fertile about half the length of its twisted or bent awn.—Dry ground. July–Sept.
3. A. marítimus, Chapm. Smooth and glaucous; culms ascending from creeping rootstocks, 1–1½° high; leaves rather rigid, divaricate, their compressed sheaths imbricated; panicle short; peduncles included within the conspicuous bracts; rhachis and pedicels copiously ciliate with spreading hairs; glumes larger, 3–4´´ long.—Sandy sea-coast; Cape May, and south to Fla.
[+][+] In pairs or clustered; the copious soft-silky hairs much longer than the flowers; sterile spikelet a small neutral rudiment (in n. 4 and 5), or altogether wanting on the very plumose-hairy pedicel; fertile flower monandrous, its awn capillary; leaves narrow, the lower or their sheaths often rather hairy.
4. A. argénteus, Ell. Smooth; culms rather slender (1–3° high); spikes in pairs (rarely in fours) on short mostly exserted and loosely paniculate peduncles, densely flowered (1–2´ long), very silky with long bright white hairs. (A. argyræus, Schultes.)—Md. to Va., near the coast, and southward.
5. A. Ellióttii, Chapm. Closely resembling the last; sheaths and leaves villous; upper nodes of the branches densely bearded.—Md. to Fla. and Tex.
6. A. Virgínicus, L. Culm flattish below, slender (2–3° high) sparingly short-branched above, sheaths smooth; spikes 2 or 3 together in distant appressed clusters, shorter than their sheathing bracts, weak (1´ long), the spikelets loose on the filiform rhachis, the soft hairs dull white. (A. dissitiflorus, Michx. A. vaginàtus, Ell., a form with larger and inflated sheaths.)—Sandy soil, E. Mass. to Va., Ill., and southward. Sept., Oct.
7. A. macroùrus, Michx. Culm stout (2–3° high), bushy-branched at the summit, loaded with very numerous spikes forming thick leafy clusters; sheaths rough, the uppermost hairy; flowers nearly as in the preceding; the sterile spikelet of each pair wholly wanting, its pedicel slender and very plumose.—Low and sandy grounds, N. Y. to Va., near the coast, and southward.