Hypericum is a genus of about 400 species of flowering plants in the family Clusiaceae, subfamily Hypericoideae (formerly often considered a full family Hypericaceae). The genus has a nearly world-wide distribution, missing only from tropical lowlands, deserts and polar regions. All members of the genus may be referred to as St. John's-worts, though they are also commonly just called hypericums, and some are known as tutsans. The marsh St. John's-worts are nowadays separated in Triadenum.

St. John's-worts vary from annual or perennial herbaceous herbs 5-10 cm tall to shrubs and small trees up to 12 m tall. The leaves are opposite, simple oval, 1-8 cm long, either deciduous or evergreen. The flowers vary from pale to dark yellow, and from 0.5-6 cm in diameter, with five (rarely four) petals. The fruit is usually a dry capsule which splits to release the numerous small seeds; in some species it is fleshy and berry-like.

30 seeds