Culms 1-2.5 m; nodes 7-12. Blades 10-25 mm wide. Panicles
10-20 cm, producing around 4,000-6,000 caryopses; lower branches about
3 cm, producing a lobed appearance. Spikelets morphologically indistinguishable
from those of var. viridis. 2n = 18.
Setaria viridis var. major is a major adventive weed in corn and
bean fields of the midwestern United States, dwarfing var. viridis in stature.
Annual herb, tufted 1 - 2.5 m tall Leaves: alternate, two-ranked. Sheaths sometimes minutely rough, fringed with hairs near the apex. Ligules 1 - 2 mm long, membranous, marginally fringed with hairs. Blades to 20 cm long, 1 - 2.5 cm wide, lance-shaped, flat, smooth or rough, parallel-veined. Inflorescence: a terminal arrangement of spikelets (panicle), dense, 10 - 20 cm long, spike-like, with numerous bristles 0.5 - 1 cm long, appearing lobed due to the short lower branches. Axis hairy. Bristles green, rarely purplish, rough. Fruit: a caryopsis, indehiscent, enclosed within the persistent lemma and palea, ellipsoid to nearly spherical. Between 4,000 and 6,000 are produced. Culm: upright or decumbent, 1 - 2.5 m long, round in cross-section, with seven to twelve nodes. Spikelets: nearly stalkless to short-stalked, about 2 mm long, lance-shaped to ellipsoid. Glumes:: Lower glumes about one-third as long as spikelets, triangular egg-shaped, three-veined, membranous. Upper glumes nearly equal to upper lemmas, elliptical, five- to six-veined. Lemmas:: Lower lemmas slightly longer than upper lemmas, five-veined, membranous. Upper lemmas pale green, hardened, finely wrinkled, five- to six-veined. Paleas:: Lower paleas about one-third as long as lower lemmas, transparent. Upper paleas similar to upper lemmas, hardened, wrinkled. Florets:: Lower florets sterile or male. Upper florets bisexual. Anthers three. Styles two. Stigmas red.
Similar species: No information at this time.
Flowering: late July to late September
Habitat and ecology: Introduced from Europe and now a common weed of waste and cultivated ground.
Occurence in the Chicago region: non-native
Etymology: Setaria comes from the Latin words seta, meaning bristle, and aria, meaning possessing. Viridis means green. Major means larger.