St. John's wort bleeds red, which is how it got its saintly name
Crush the tiny dark dots on a St. John's wort leaf or petal and they leave a red stain. In the 16th century Paracelsus called the secretion John's blood, tying the plant to the martyred St. John. The colour comes from hypericin and pseudohypericin, pigments packed into glands found across much of the genus.
Hypericum holds more than 490 species and grows almost everywhere except tropical lowlands, deserts and polar regions. Every member can be called St. John's wort. It is unusual for such a large genus to have a complete worldwide monograph, but Norman Robson of the Natural History Museum in London produced one, dividing the genus into 36 sections. The Greek source name may mean above pictures, from hanging the plant over shrines to ward off evil spirits.
Botanists rely on small details to tell species apart. Leaves are almost always paired at right angles to the pair below, and thin ridges run down the stems; common St. John's wort has two such lines while the similar Hypericum maculatum has four. Petals are nearly always yellow, from pale lemon to deep orange-yellow, though a few species are white or pinkish and one variety is deep crimson. A flower may hold anything from five to two hundred stamens. Growth forms range from annual herbs to shrubs and rare single-stemmed trees.
Common St. John's wort, H. perforatum, is a problem plant in temperate farmland on several continents and is considered poisonous to livestock. Part of its success comes from escaping its natural pests, so beetles such as Chrysolina quadrigemina and a root-boring beetle have been released as biological controls.
The same species is widely sold, especially in Europe, as an herbal remedy for depression. The evidence carries warnings: combining it with prescription antidepressants may cause a dangerous rise in serotonin, and it reduces the effectiveness of hormonal contraceptives. Gardeners grow other species for their big showy flowers. The oldest fossil in the genus, Hypericum antiquum, comes from Eocene rocks in Siberia, and Miocene seeds have turned up in the Czech Republic and in Jutland.
Source: Hypericum
