Mant. Pl. 1: 106. 1767.
Shrubs, erect or ± diffuse, forming rounded or irregular bush, (2–)7.5–15(–20) dm. Stems: internodes 4-lined at first, then 2-lined to terete. Leaf blades narrowly oblong to narrowly elliptic-oblanceolate, 30–70 × 6–15 mm, base articulated, attenuate to narrowly cuneate, margins plane to recurved, apex rounded-apiculate to acute, midrib with 10–16 pairs of branches. Inflorescences cylindric, (1–)3–7(–9)-flowered from apical node, with paired single flowers or triads or 1–3(–7)-flowered branches from 2+ proximal nodes. Flowers 15–30 mm diam.; sepals deciduous, not enclosing capsule, 5, elliptic to obovate or oblanceolate-spatulate, unequal or subequal, 4–8 × 1.5–4 mm; petals 5, golden yellow, obovate to oblanceolate-spatulate, 7–15 mm; stamens deciduous, 150–500; ovary 3(–5)-merous, placentation incompletely axile. Capsules usually narrowly ovoid-conic to ovoid, rarely ellipsoid, 7–13 × 4–7 mm. Seeds carinate, 1.5–2 mm; testa linear-reticulate. 2n = 18.
Phenology: Flowering summer (Jun–Sep).
Habitat: Rocky slopes, embankments, dry stream bottoms, woodland (in north), on limestone or granite
Elevation: 50–600+ m
Ont., Ala., Ark., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Ky., La., Md., Mich., Miss., Mo., N.J., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va., Wis.
Hypericum prolificum is variable, the most luxuriant form being found in the southwestern part of its range. Natural hybrids have not been recorded; it hybridizes in gardens with H. densiflorum (H. x\arnoldianum Rehder), H. frondosum, H. kalmianum, and H. lobocarpum (H. x\dawsonianum Rehder).