Spikelets spiked or somewhat racemed, in 2–4 rows on one side of a flattened or filiform continuous rhachis, jointed upon very short pedicels, plano-convex, awnless, 1-flowered. Glumes 3 (rarely only 2), the terminal one flowering. Flower coriaceous, mostly orbicular or ovate, flat on the inner side, convex on the outer. Stamens 3. Spikes one or more, at or toward the summit of an elongated peduncle. (Πασπάλος, a Greek name for Millet.)
[*] Spikes with a (1´´) broad and thin membranaceous or foliaceous and keeled rhachis, the incurved margins partly enclosing the small two-rowed spikelets. (Smooth, aquatic, or nearly so, decumbent or floating.)
1. P. flùitans, Kunth. Annual; leaves lanceolate, flat (3–8´´), broad; spikes numerous in a raceme, the rhachis somewhat projecting beyond the minute and slightly pubescent spikelets into a tapering point, scabrous on the back.—River-swamps, Va. to S. Ill., Mo., and southward. Sept., Oct.
2. P. Walteriànum, Schultes. Perennial; leaves linear, short; spikes 3–7, the lowest partly included in the sheath of the uppermost leaf, the rhachis blunt; spikelets glabrous.—Low or wet grounds, N. J. (Cape May, Nuttall), Del., and southward.
[*][*] Spikes with a narrow wingless rhachis; perennials, or mostly so.
[+] Spikelets very obtuse, orbicular; spikes one terminal and often 1–5 lateral.
3. P. setàceum, Michx. Culm ascending or decumbent (1–2° long), slender; leaves (2´´ wide, flat) and sheaths clothed with soft spreading hairs; spikes very slender (2–4´ long), smooth, mostly solitary on a long peduncle, and usually one from the sheaths of each of the upper leaves on short peduncles or included; spikelets (½´´ wide) narrowly 2-rowed.—Sandy fields; common from E. Mass. to Ill., and southward. Aug.
4. P. læ̀ve, Michx. ([Pl. 13], fig. 1–3.) Bright green, sparingly villous, rather stout; stems somewhat decumbent; leaves and spikes widely spreading; spikes (2–4) approximate, 2–4´ long, smooth or nearly so; spikelets about 1´´ wide, 2-rowed.—Moist soil, S. New Eng. to Ky., and southward.
5. P. Floridànum, Michx. Stout, erect, 3–6° high, glaucous; sheaths and leaves more or less villous, the latter and the spikes erect or ascending; spikes (2–5) broader, 2–5´ long, the smooth spikelets nearly 2´´ broad, in 2 rows.—Moist soil; Del. to Fla., Ark., and Tex.
[+][+] Spikelets acute; spikes several, racemose.