1. Fimbristylis annua (All.) Roem. &
Pl. 77 j, k; Map 286
Plants annual, tufted,
lacking rhizomes. Stems few to many, 5–30 cm long, erect to spreading,
glabrous or less commonly minutely hairy. Leaves with blades 2–15 cm
long, glabrous or hairy, especially along the usually flat margins, the top of
the sheath with a ligule consisting of a line of short hairs. Inflorescences
usually umbels, sometimes partially with compound umbels, the 2–4 bracts
shorter than to about twice as long as the inflorescence, at least some of the
spikelets usually short- to long-stalked, not hidden by the inflorescence
bracts. Spikelets 3–8 mm long, lanceolate to ovate or less commonly
oblong in outline, usually pointed at the tip, the scales 1.1–1.4 mm
long, broadly oblong to ovate, the tip pointed or rounded, the midvein rarely
extended past the scale tip as a short point, glabrous, dark brown to reddish
brown with thinner, lighter, narrow margins, the midvein usually green. Stamens
1–2. Stigmas 2, the style usually fringed below the branches. Fruits
0.9–1.2 mm long, obovate in outline, slightly flattened (biconvex) in
cross-section, the surface reticulate, ribbed with 9–25 vertical rows of
cells, sometimes also sparsely warty along the ribs, light yellow to tan, often
somewhat iridescent. 2n=30. June–October.
Widely scattered in
Missouri, south of the Missouri River (North America to South America, Caribbean;
also in the Old World tropics and subtropics). Prairies, moist areas of glades,
and margins of ponds, lakes, streams, and rivers, usually in sandy or gravelly
soils, often on acidic substrates.
This species is
sometimes treated as a temperate variant of the widespread, tropical F.
dichotoma (L.) Vahl, a more robust perennial with stiffer leaves and
usually smoother fruits.