Hypericum perforatum is a perennial, 3 herb (Pooter et al. 1990), 40-80 cm tall, colonial (in some parts of the USA) from rhizomes, branches numerous, upturned, opposite, leafy, each pair at right angles to next (decussate) many winter-green, leafy shoots at base, often mat-forming, stems sharply ridged below leaf bases.
Leaves opposite, simple, stalkless, linear-oblong, 2-4 cm long on main stem, smaller on branches, marked with tiny clear dots.
Flowers yellow, numerous, petals 0.8-1.2 cm long, often black-dotted near margin, sepals 0.4-0.6 cm long tips long-pointed, with few or no dots, self-fertile (agamospermy), stamens numerous, in groups, fused at base, styles 3, divergent (Mulligan and Kevan 1973); blooms and fruits June-Sept.
Fruit red, drying brown, cone-shaped, 3-parted capsule, cupped in old calyx, often with a fringe of old stamens at base, splitting open to release numerous oblong seeds about 0.1 cm long.
Wetland status: UPL.
Frequency in NYC: Infrequent.
Habitat: Open, weedy areas. Found in fill soil with pH 7-8.
Notes: Overwintering leafy shoots give St. John’s-wort a competitive advantage in spring (Crompton et al. 1988). Used as a medicinal since ancient times but effectiveness is unproven. May interact with certain drugs (NCCAM, NIH. 2007). Contains a photosensitizing pigment, hypericin, causing increased risk of sunburn from blue and longer wave ultraviolet light (540, 590 mµ). Hypericin consists of multiple, fused benzene rings (a napthodianthrone derivative, appearing like 8 floor-tiles if drawn in a standard chemical formula) (Kingsbury 1964). Listed as a noxious weed in a number of western states as it is toxic and proliferates rapidly (USDA, NRCS 2006). Is eaten by the klamath weed beetle, Chrysolina quadrigemina, a beetle in the family Chrysomelidae. This insect has been an effective biological control on the spread of klamath weed in western states. Can be infected by Colletotrichum gloeosporioides (Crompton et al. 1988).