6. Setaria viridis (L.) P. Beauv. (green foxtail)

Pl. 175 e–g; Map 707

Plants annual, with soft bases, without rhizomes. Flowering stems 20–250 cm long, rarely slightly flattened, glabrous. Leaf sheaths rounded on the back to slightly keeled, hairy along the margins and glabrous or more commonly roughened on the surface, the ligule 1–3 mm long. Leaf blades 4–40 cm long, 3–25 mm wide, flat, the upper surface roughened, the undersurface roughened or less commonly glabrous. Inflorescences 3–20 cm long, erect or somewhat nodding or drooping toward the tip, the short branches reduced to clusters of spikelets (the inflorescence then appearing cylindrical) or the lowermost branches sometimes slightly elongate and appearing more distinct (the inflorescence then appearing somewhat lobed), but not in definite whorls, the main axis with short, soft, upwardly pointing hairs and often also with longer, soft, ascending to spreading hairs, the spikelets subtended by 1–3 green or rarely purple bristles, these 5–12 mm long. Spikelets 1.6–2.5 mm long, disarticulating below the glumes. Lower glume 0.5–1.2 mm long. Upper glume 1.6–2.2 mm long. Lowermost floret usually sterile, 1.5–2.5 mm long. Fertile floret with the lemma 1.6–2.1 mm long, with noticeable, fine cross‑wrinkles on the surface. Anthers 0.4–0.8 mm long. 2n=18, 36. June–October.

Introduced, scattered to common nearly throughout Missouri (presumably a native of Europe, Asia; introduced and weedy in the U.S., Canada, Mexico, Caribbean Islands). Margins and disturbed openings of mesic upland forests, upland prairies, banks of streams and rivers, and margins of ponds and lakes; also pastures, fallow fields, crop fields, levees, lawns, gardens, sidewalks, roadsides, railroads, and open, disturbed areas.

Setaria viridis is a quite variable species in which two overlapping varieties may be recognized. It is a serious weed of crop fields.