Common St John’s-wort

Common St John’s-wort (Hypericum perforatum) grows throughout Britain on grasslands and also next to hedges and in open woods, having a preference for chalky soils.

It throws up hairless erect stems that are woody at the base. This variety of St John’s-wort can be identified by the two narrow ribs that run up the stems on opposite sides. The small leaves are noticeable for appearing to be punctured if seen against the light (hence “perforatum”), although these are tiny translucent glands.

The flowers, which appear from June to September, are an inch across and have five widely-spaced yellow petals that have black dots on the edges. The stamens are in three bundles, which correspond to the three cells that are apparent in the seed capsule when it forms.

Common St John’s-wort was used extensively in medieval times as a medicinal plant. It was a stipulation of medieval herbal medicine that if a plant resembled a part of the human body then it had been made that way by God because it would cure diseases and injuries of that part. No part of common St John’s-wort has this correspondence, but the “punctures” on the leaves were thought to symbolise wounds, so the plant found a use in treating wounds, particularly if received in battle.

The name of the plant derives from this use, because it was part of the medical kit of the Knights of St John of Jerusalem during the Crusades.

Common St John’s-wort was also believed to have the power to drive away evil spirits. People would hang bunches of it over their doorway to keep the Devil at bay. If somebody believed that they had been possessed by a devil they would try prayer as their first resort but St John’s-wort as their second, wearing it on their person or strewing their cottage floor with it. 

© John Welford