St. Johnswort (Hypericum perforatum L.)

Identification

St. Johnswort is a perennial that reproduces by seeds and short horizontal roots. The multi-branched stems can grow up to 2 1/2 feet tall and emerge from a woody base. The flowers have numerous stamens, are bright yellow and have five petals which have black dots on their margins. Showy clusters of flowers occur on the ends of the stems. Leaves are opposite with translucent dots along the margins, the dots are visible when the leaf is held up to a light source.

St. Johnswort is typically found invading overgrazed pastures. This aggressive plant may be toxic to white-haired animals – it causes photosensitization (sensitive to sunlight). St. Johnswort is commonly used in herbal remedies as a “mood booster”.