Imperforate St. John's-wort
- Written also: Imperforate St John’s-wort, Imperforate St John’swort
- Family: St. John’s-wort Family – Hypericaceae
(formerly Clusiaceae, also known as Guttiferae)
- Height: 30–80 cm (12–32 in.). Usually single-stemmed. Stem 4-edged, hollow, glabrous, upper part sparsely branched, woody at base.
- Flower: Regular, 2–3 cm (0.8–1.2 in.) broad. Petals 5, yellow, varyingly dotted and streaked with black. Sepals 5, blunt, with entire margins and black-dotted. Stamens many, fused at base into 3 bunches. Pistil of 3 fused carpels. Inflorescence a quite sparsely-flowered cyme.
- Leaves: Opposite, stalkless. Blade broadly elliptic, round-tipped, glabrous, margin flat (not revolute), edges often black-spotted.
- Fruit: Brown, quite round, 3-parted capsule.
- Habitat: Young meadows, pastures, forest margins, road-sides, railway embankments.
- Flowering time: July–September.
The St. John’s-wort family (Hypericaceae) is mainly comprised of tropical and sub-tropical wood-stemmed species. This background is apparent in many of these kinds of species in the family that are classed as being herb-stemmed because its aerial parts are annual. Herb-stemmed imperforate St John’s-wort’s stem becomes woody at its base so that when the cells die it is able to remain upright throughout the winter and spread its seeds across the snow, especially in spring when it has a crust. The seeds germinate early to flower the next spring, but they can also survive a long time without germinating. The plant’s rest period is not strict as new, overwintering green parts begin to germinate already in the autumn. It is classed as a hemicryptophyte. Imperforate St John’s-wort can be most easily differentiated from other St John’s-worts by its four-edged stem and round-tipped sepals.