2. Fimbristylis autumnalis (L.) Roem. &
Pl. 77 a–c; Map 287
var. mucronulata (Michx.) Fernald
Plants annual, tufted,
lacking rhizomes. Stems few to many, 5–35 cm long, erect to ascending,
glabrous. Leaves with blades 2–10 cm long, glabrous, the margins flat,
the top of the sheath with a ligule consisting of a line of short hairs.
Inflorescences usually compound umbels, sometimes only simple umbels, the
2–3 bracts shorter than to longer than the inflorescence, at least some
of the spikelets usually short- to long-stalked, not hidden by the
inflorescence bracts. Spikelets 3–7 mm long, lanceolate to narrowly
elliptic in outline, pointed at the tip, the scales 1.0–1.3 mm long,
broadly lanceolate, the tip pointed, the back usually strongly keeled, the
midvein extended past the scale tip as a short point, glabrous, brown to dark
brown with the midvein usually green. Stamens 1(2). Stigmas 3, the style smooth
below the branches. Fruits 0.9–1.1 mm long, obovate in outline, strongly
3-angled in cross-section, the surface smooth to sparsely warty, light brown to
tan. 2n=10. June–October.
southern Missouri and locally north along floodplains of rivers (U.S. and adjacent Canada south to Central America, Caribbean Islands; also in the Old World
tropics). Sandbars, gravel bars, and mudflats along streams and rivers, margins
of ponds and lakes, moist depressions of upland prairies and glades, sandy
fields, and moist, disturbed, sandy areas.