Perennial herb 30 cm - 0.8 m tall Stem: usually unbranched below the inflorescence, scattered. Leaves: opposite, 3 - 6 cm long, 5 - 10 mm wide, linear-oblong to narrow elliptic with a tapered base and pointed tip, non-toothed and curling under slightly (revolute). Flowers: borne in a many-flowered, multi-branched, compact inflorescence, subtended by tiny awl-shaped bracts, with lance- to egg-shaped sepals 2 - 7 mm long, five yellow petals 6 - 8 mm long, 45 to 85 stamens, and three styles attached for most of their length. Fruit: a one-chambered capsule, 4 - 6 mm long, egg-shaped, narrowing to an elongated beak formed from the persistent styles, containing many seeds.
Similar species: Hypericum adpressum, Hypericum ascyron, Hypericum perforatum, Hypericum punctatum, and Hypericum sphaerocarpum have more than 30 stamens per flower. 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 punctatum differs because it has non-angled and black-spotted stems with little branching below the inflorescence, its leaves are over 1 cm wide and covered with black dots, the flowers have sepals and petals covered with black dots and 30 to 60 stamens, and the seeds are nearly or entirely smooth and less than 1 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 June to early September
Habitat and ecology: This species grows in wet sandy prairies and in moist sandy soil along marsh borders and in ditches.
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). Adpressum means appressed.
Rhizomatous herb 3-8 dm, coarser than no. 10 [Hypericum ellipticum Hook.], usually simple to the infl; lvs many, linear-oblong to narrowly elliptic, 3-6 cm נ5-10 mm, revolute, acute or subacute, tapering to the base; infl usually with many fls; bracts minute, subulate; sep lanceolate to ovate, 2-7 mm; pet 6-8 mm; stigmas 3(4), minute; fr ovoid, 4-6 mm, gradually narrowed to the beak, unilocular but with intruded placentas; 2n=18. Marshes, shores, and wet meadows; e. Mass. to Ga. and Tenn., and occasionally inland to Ind. and Ill. July, Aug.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.