4. Digitaria ischaemum (Schreb.) Schreb. ex Muhl. (smooth crab grass)

Pl. 161 f, g; Map 652

D. ischaemum var. mississippiensis (Gatt.) Fernald

Plants annual, forming loose tufts. Flowering stems 20–50(–70) cm long, erect or ascending from spreading bases, uncommonly rooting at the lowermost nodes. Leaf sheaths glabrous or with sparse hairs along the margins near the tip, the ligule 0.6–1.8 mm long. Leaf blades 2–20 cm long, 3–9 mm wide, glabrous. Inflorescences of (1–)2–8 spikelike racemes, these 1–15 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 relatively broadly winged, the wings as wide as or wider than the midrib of the axis. Spikelets 1.7–2.3 mm long, elliptic in outline. Upper glume 1.5–2.3 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 1.5–2.3 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 1.5–2.3 mm long, ovate‑elliptic, sharply pointed at the tip, dark brown to purplish brown at maturity. Anthers 0.4–0.6 mm long, yellow. 2n=36. August–October.

Introduced, common nearly throughout the state (native of Europe, Asia; introduced widely in the U.S. and Canada). Bottomland forests, mesic upland forests, moist depressions of upland prairies, bases of bluffs, banks of streams and rivers, and margins of ponds and lakes; also crop fields, fallow fields, pastures, lawns, roadsides, railroads, and moist, disturbed areas.

Robust individuals have been called var. mississippiensis. Steyermark (1963) noted the existence in Barry County (and perhaps elsewhere) of rare, unusual plants with the spikelets all or mostly replaced by vegetative bulblets on short, branched stalks.