Syst. Veg. 1: 805. 1824.
Plants subshrubs, perennial, 30–80(–100) cm, from thick rhizome with fibrous roots. Stems 1 or several-clustered, erect, simple, usually hairy, sometimes glabrous or subglabrous. Leaves: proximal and distal alternate, petiolate, distalmost sessile or nearly so; stipules narrowly elliptic to linear or lanceolate, (0.5–)4–25(–30) mm, sparsely hirsute; petiole 6–20 mm; blade elliptic or oblanceolate, 6.5–17 × 1.5–6 cm, base attenuate or acuminate, margins entire or sparsely serrate, ciliate or eciliate, apex acute to long-acuminate, surfaces usually strigose and/or sericeous, sometimes glabrous, trichomes scattered throughout or concentrated along outer margins, veins, or petiole. Inflorescences 1–3-flowered; peduncle recurved at anthesis, becoming erect, 5–23 mm, pilose; bracteoles present. Flowers: sepals often spreading from corolla, linear to linear-lanceolate, margins ciliate or eciliate, apex acute; petals: upper and laterals greenish white, oblong, 3.5–5 mm, margins usually with scattered cilia, apex usually truncate and recurved, glabrous; lowest greenish white, 4–5.5 mm, claw 0–1 × 3–4 mm, usually longer and wider than others, distal limb oblong, ± flat to convex, 3–5 mm wide, apex retuse, sometimes rounded, usually glabrous; cleistogamous flowers, when present, from axils of distal leaves. Capsules oblong to ellipsoid, (8–)15–20 mm. Seeds 6–9, white to cream, globose to broadly ovoid, (3–)4–7 mm. 2n = 48.
Phenology: Flowering Apr–early Jul.
Habitat: Rich, limestone soil and talus in woodlands, slopes, ravines
Elevation: 100–1000 m
Ont., Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., Md., Mich., Minn., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Vt., Va., W.Va., Wis.
R. E. Brooks and R. L. McGregor (1986) reported that no cleistogamous flowers have been seen on plants of Hybanthus concolor collected in the Great Plains. It is believed extinct in Connecticut and is listed as endangered in Florida.