Perforate St. John's-wort
- Name also: Common St. John’s-wort, Perforate St John’s-wort. Perforate St. Johnswort, Tipton’s Weed, Klamath Weed, Goatweed
- Family: St. John’s-wort Family – Hypericaceae
(formerly Clusiaceae, also known as Guttiferae)
- Growing form: Perennial herb.
- Height: 30–80 cm (12–32 in.). Many-stemmed. Stem upper part abundantly branched, 2-edged, glabrous, woody at base.
- Flower: Regular, 1.5–3.5 cm (0.6–1.4 in.) broad. Petals 5, yellow, dotted and streaked with black. Sepals 5, tapered, mostly with entire margins, usually 3-veined. Stamens many, fused into 3 bunches. Pistil of 3 fused carpels. Inflorescence an abundantly flowered cyme.
- Leaves: Opposite, stalkless, weakly amplexicaul. Blade lanceolate–elliptic, with black and especially translucent dots, margins slightly revolute.
- Fruit: 3-parted capsule.
- Habitat: Rocky hills and juniper groves, warm rocky embankments, commons.
- Flowering time: July–September.
Perforate St John’s-wort is many-stemmed, and its stems are full and two-edged. It is a perennial that favours dry, light-filled habitats. It can also be differentiated from its close relative imperforate St John’s-wort (H. maculatum) by the way that its sepals have tapered tips. Like other parts of the stem, and typically of St John’s-wort species, the leaves have oil cavities that appear as translucent spots. Perforate St John’s-wort often spreads apomictically, i.e. without being fertilised.
Perforate St John’s-wort is a diverse useful plant – and actually imperforate St John’s-wort has probably also been used because the species have doubtless sometimes been confused. Their known active constituent is hypericin, which the plant manufactures to protect it from being eaten. In its early stages it yields good red and violet dyes, and textile dyes are extracted form the root in particular, but also the buds. Perforate St John’s-wort has been used medicinally to treat e.g. internal parasites, boils and ulcers, and fever. It was formerly used to make Fuga daemoniumia – devil chaser – to treat depression, but the cure was often worse than the disease as it was administered in large doses and the patient often died. Perforate St John’s-wort is toxic, so it is best not to collect it on one’s own. In Finland the species is generally harmless and useful. From Europe and Asia the species has spread with people to many countries, including Australia, New Zealand and North America where it has become a troublesome weed in its new habitats.