3. Digitaria filiformis (L.) Koeler (slender crab grass)

Pl. 161 a, b; Map 651

Plants annual, forming tufts. Flowering stems 30–80(–150) cm long, erect or ascending, usually not rooting at the lowermost nodes. Leaf sheaths glabrous or hairy, the ligule 0.3–1.1 mm long. Leaf blades 2–25 cm long, 2–6 mm wide, glabrous, roughened, or sparsely hairy. Inflorescences of 2–6 spikelike racemes, these 3–25 cm long, arranged digitately at the tip of the main inflorescence axis or in a panicle with a short main axis, the spikelets with stalks 0.5–3.0 mm long, grouped in 2 rows on 1 side of the axis of the spikelike raceme, this very narrowly winged, the wings narrower than the midrib of the axis. Spikelets 1.5–2.8 mm long, elliptic in outline. Upper glume 1–2 mm long, elliptic, sharply pointed at the tip, sparsely to densely pubescent with minute, gland‑tipped hairs (mostly between the nerves). Sterile floret with the lemma 1.5–2.8 mm long, elliptic, sharply pointed at the tip, sparsely to densely pubescent with minute, gland‑tipped hairs (mostly between the nerves). Fertile floret with the lemma 1.5–2.8 mm long, ovate‑elliptic, sharply pointed at the tip, dark brown at maturity. Anthers 0.3–0.6 mm long, yellow. 2n=36. August–October.

Scattered, mostly south of the Missouri River (eastern U.S. west to Iowa and Texas; Mexico, Central America, Caribbean Islands). Prairies, sand prairies, glades, savannas, and openings of dry upland forests, usually on acidic substrates; also pastures, old fields, roadsides, railroads, and open, disturbed areas.

Two varieties are recognized for Missouri. Wipff (1996b) has suggested the separation of additional varieties, based upon localized populations elsewhere in the species’ range, but he did not treat these in sufficient detail to allow further discussion here.