Common St. Johnswort

(Hypericum perforatum)


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© CSU Extension
© CSU Extension

Common St. Johnswort (Hypericum perforatum) is a perennial forb native to Europe and frequently found in the Pacific Northwest. Common St. Johnswort grows to a height of 1 to 3 feet tall, with multiple branched stems. The stems are erect, ridged, rust colored, and woody at the base. The elliptical to oblong shaped leaves are no longer than 1 inch, covered with clear dots, and are opposite of each other on the stems. The flowers are bright yellow and about 3/4 of an inch in diameter. They appear in showy terminal clusters, have five petals and numerous visible stamens. Rust-brown seed pods are formed after flowering. Seed pods are about 1/4 inch in length and contain numerous amounts of seeds. One plant can produce up to 100,000 seeds per year. The root system consist of a large taproot and fiberous roots near the surface. The plant reproduces by seeds or short runners.

Common St Johnswort Factsheet pdf file