Plants perennial. Stems 0.75-1.5 m, glabrous or slightly pubescent. Leaf blades ovate-elliptic, 2.5-13.5 × 0.2-6.8 cm, base tapering, apex acute to acuminate, pubescent on veins abaxially, short-pubescent adaxially, varying to glabrous or glabrescent. Inflorescences 2-4 cm in flower, elongating to 21 cm in fruit; bracteoles spinose; basal wings attached at base and sometimes slightly on sides. Flowers: tepals 5, 4-5 mm; pseudostaminodes with margins entire, denticulate, or slightly 2-lobed at apex. Utricles elliptic, 2.5 mm.
Perennial 7-15 dm; lvs elliptic, 3-13 נ1.5-7 cm, acute or acuminate, tapering to a petiole to 3.5 cm, short-hairy above and on the veins beneath; spikes at first dense, elongating to as much as 2 dm and then more open; fls divergent at anthesis, sharply reflexed in fr, each subtended by a membranous bract 2 mm and 2 rigid, subulate-spinose bracteoles 2-4 mm, each bracteole with 2 basal, suborbicular, membranous auricles, the bracteoles and fl falling as a unit; sep 5, lance-linear, 4-5 mm, acuminate; sterile lobes of the androecium short, broad, subentire; fr oblong, 2.5 mm, its slender style 1 mm. Wooded, annually flooded river-banks; native of e. Asia, intr. in Ky. and W.Va. Late summer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Indiana Coefficient of Conservatism: C = null, non-native
Wetland Indicator Status: N/A
Diagnostic Traits: leaves opposite, elliptic, to 13 cm; inflorescences include unbranched, many-flowered terminal spikes; flowers reflexed with age, their tepals fused at base, glabrous.
Japanese Chaff Flower was first reported in Indiana in 2002 and now has spread throughout our Ohio Valley region. This invasive species favors partial shade and moist soil, making it an ideal floodplain weed.