Hypericum tetrapterum (syn. Hypericum quadrangulum) | ‘Peterwort’, ‘Square-stalked St. John’s Wort’, ‘Square-stemmed St. John’s Wort’, ‘St. Peter’s Wort’ | Seeds
Most commonly known as the ‘Square-stalked St. John’s Wort’ or ‘Square-stemmed St. John’s Wort’, Hypericum tetrapterum (syn. Hypericum quadrangulum) is an erect herbaceous flowering perennial species of the Hypericaceae. Also known as the ‘Peterwort’ or ‘St. Peter’s Wort’, tetrapterum is common to Europe and the United Kingdom, where it prefers fertile damp or wet soils in habitats such as ditches, marshes, meadows, riverbanks and other watercourses.
Spreading by both seed and rhizomes, Hypericum tetrapterum grows to around sixty to ninety centimetres tall, forming stout and hardy stems that spread from the base. The stems are square in cross section and have four ridges running along their length, providing the species with its common name. Tetrapterum’s green, rounded to oval and hairless leaves grow in opposite pairs and are speckled with translucent dots (unlike most of the ‘St John’s Wort’ complex, which usually display black glandular dots). Pale to bright yellow flowers appear between June and September, reaching from nine to thirteen millimetres in diameter.
Being tolerant of a wide range of growing conditions, Hypericum tetrapterum is fairly easy to grow from seed. It’s best sown in Autumn for a Spring germination, in full sun to partial shade. Plant in the ground or containers, keeping the soil damp to wet at all times.
All the seed sold by Arkham’s Botanical was freshly and ethically sourced in 2018-2019