Ascyrum microsepalum Torrey & A. Gray, Fl. N. Amer. 1: 157. 1838; Crookea microsepala (Torrey & A. Gray) Small; Isophyllum drummondii Spach

Shrubs, erect to ascending, bushy, with ± numerous, sometimes straggling branches, 1.5–7 dm. Stems: internodes 4-lined at first, eventually 2-lined. Leaf blades narrowly oblong or oblanceolate to linear, 5–15 × 1–3 mm, base not articulated, rounded to cuneate, margins recurved to subrevolute, apex rounded to obtuse, midrib with 1–3 pairs of branches. Inflorescences <rounded-pyramidal>, 1–3-flowered, narrowly branched, sometimes with 1–3-flowered dichasia or branches from to 4 proximal nodes. Flowers 15–25 mm diam.; sepals persistent, not enclosing capsule, (3–)4(–5), oblong or elliptic-oblong to linear, subequal or equal, 3–5 × 1–1.4 mm; petals (3–)4(–5), bright yellow, obovate (larger pair) to obovate-oblong (smaller pair), 10–12 mm; stamens persistent, 60–70; ovary 3-merous, <placentation parietal>. Capsules cylindric-ellipsoid to narrowly ovoid-conic, 6–8 × 2.5 mm. Seeds not carinate, 0.9–1 mm; testa linear-foveolate. 2n = 18.

Flowering late winter–spring (Feb–May), late fall (Nov). Low, pine flatwoods, moist to wet, on sand; 0–100 m; Fla., Ga.

Hypericum microsepalum is related to H. cistifolium, not to the other four-petaled species attributed to Ascyrum, and can be distinguished from it by the bushier habit and smaller leaves and by the usually four-merous flowers with larger petals.

Hypericum isophyllum Steudel is an illegitimate name for H. microsepalum.