Hypericum tetrapterum

Hypericum tetrapterum (syn. H. quadrangulum) is a herbaceous perennial plant species in the flowering plant family Hypericaceae. Its common names include St. Peter's wort, Peterwort, square stemmed St. John's wort, and square stalked St. John's wort.

Description
Hypericum tetrapterum is a rhizomatous, glabrous perennial plant growing up to 1.2 m in height. The stems are square in cross section, with conspicuous wings at the corners. The leaves are in opposite pairs, simple and entire, and have many translucent glandular dots. The thinly papery leaves are up to 40 mm long and 24 mm across and paler underneath. The flowers are produced in flowerheads of 10–30 flowers (up to 70), each flower 10–15 mm in diameter with 5 pale yellow petals and 5 sepals. There may be black glands on the petals and sepals, as well as on the leaves.

Distribution and habitat
Hypericum tetrapterum is common in damp habitats such as marshes, streamsides, open ditches, meadows, and springs throughout Europe.