Perennial herb 0.5 - 1 m tall Stem: erect, with little branching below the inflorescence, round in cross section, covered with tiny black dots. Leaves: opposite, stalkless, larger leaves 4 - 6 cm long and over 1 cm wide, oblong-elliptic to narrow oblong with a blunt to slightly notched tip, non-toothed, covered with black dots. Flowers: borne in a small, many-flowered, highly branched and compact inflorescence. The sepals are 2.5 - 4 mm long, egg-shaped to oblong with a rounded to pointed tip and are covered with black dots. Flowers also have five petals that are yellow with amber to black dots and 4 - 7 mm long, 30 to 60 stamens, and unattached styles 2 - 4 mm long. Fruit: a three-chambered capsule, 4 - 7 mm long, containing many smooth seeds less than 1 mm long.
Similar species: Hypericum adpressum, Hypericum ascyron, Hypericum perforatum, Hypericum punctatum, and Hypericum sphaerocarpum have more than 30 stamens per flower. Hypericum adpressum is distinguished because it is 30 cm - 0.8 m tall, the stems are usually unbranched below the inflorescence, the leaves are linear-oblong to narrow elliptic and curl under slightly, the flowers are less than 3 cm wide with 45 to 85 stamens and three styles that are attached for most of their length, and the capsules are less than 1 cm long and are beaked at the tip. Hypericum ascyron is 0.7 - 1.5 m tall, the leaves sometimes clasp around the stems, the flowers are 4 - 6 cm wide with 12 - 22 mm long petals, five styles, and numerous stamens, and the capsules are 1.5 - 3 cm long and lack a beak. Hypericum perforatum has highly branched stems, usually less than 1 cm wide leaves with the midrib continuing down the stem as a sharp ridge, sepals lacking or with few black glands, petals having black glands concentrated along the margins, 50 to 80 stamens, and rough seeds that are 1 - 1.3 mm long. Hypericum sphaerocarpum is 30 cm - 0.7 m tall, the stems are often clustered and become woody toward the base, the flowers are less than 3 cm across and have three united styles that separate near the tip and 45 to 85 stamens, and the one-chambered capsules are 5 - 7 mm long and narrow-beaked.
Flowering: late July to late August
Habitat and ecology: Locally common in a range of habitats, usually in semi-shade. It is especially common in weedy woodland borders.
Occurence in the Chicago region: native
Etymology: Hypericum is the Greek name for St. John's Wort, which blooms around St. John's Day (June 24). Punctatum means spotted, referring to the many black dots covering the sepals, petals, stems and leaves.
Erect perennial 5-10 dm, with few branches below the infl; lvs oblong-elliptic to narrowly oblong, the larger 4-6 cm and over 1 cm wide, blunt or even retuse; infl usually small, crowded; fls short-pediceled, 8-15 mm wide; sep heavily dotted and lined with black, ovate-oblong, obtuse or broadly acute, 2.5-4 mm; pet 4-7 mm, copiously beset with amber glands; seeds under 1 mm; 2n=16. Moist or dry soil, fields, and open woods; Que. to Minn., s. to Fla., Miss., and Okla. June-Aug. (H. subpetiolatum)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.