24. Panicum rigidulum Bosc ex Nees (redtop panic grass)

Pl. 171 a, b; Map 685

P. rigidulum var. elongatum (Pursh) Lelong

P. agrostoides Spreng.

P. agrostoides var. condensum (Nash) Fernald

P. agrostoides var. ramosius (Mohr) Fernald

P. stipitatum Nash

Plants perennial, with hardened, knotty, bases, but lacking rhizomes or stolons, forming clumps. Flowering stems 40–150 cm long, relatively stout and stiff, flattened nearly the entire length, glabrous. Leaves scattered along the stems. Leaf sheaths keeled on the back, glabrous or sometimes hairy at the tip, the ligule 0.3–1.0 mm long, a short, uneven membrane. Leaf blades 8–50 cm long, 3–9(–12) mm wide, firm, arched or spreading, glabrous or nearly so, the margins roughened and sometimes inrolled. Inflorescences 8–30 cm long, with the primary branches ascending to spreading, not spikelike, rebranched 1 or more times, the spikelets not appearing 1‑sided, mostly short‑stalked, not curved or angled with respect to their stalks. Spikelets 1.5–2.8 mm long, narrowly elliptic‑ovate in outline, sharply pointed at the tip, glabrous. Lower glume 0.8–1.5 mm long, 1/2–2/3 as long as the rest of the spikelet, elliptic to obovate, sharply pointed at the tip, 3‑ or 5‑nerved. Upper glume 1.5–2.8 mm long, narrowly elliptic, sharply pointed at the tip, usually 5‑nerved. Lowermost floret staminate or sterile and with a well‑developed but not hardened palea, the lemma 1.5–2.8 mm long, narrowly elliptic, 5‑nerved. Fertile floret 0.8–1.6 mm long, narrowly ovate, rounded to bluntly pointed at the tip. Anthers 0.2–0.4 mm long. 2n=18. July–October.

Scattered in the southern two‑thirds of the state (eastern U.S. west to Michigan, Kansas, and Texas; Caribbean Islands). Moist depressions of upland prairies, fens, banks of streams, margins of ponds and sloughs, and less commonly openings of bottomland forests; also moist, disturbed areas.