• Common StJohnswort Plant Mature 215x150

Category A Weed

Sunflower family (Asteraceae)

Helpful Links

List of all Photo Credits

Common St. Johnswort (Hypericum perforatum)


    • Up to 4 ft. tall with a woody base; highly branched; lacks hair (glabrous) and often rust colored with 2 ridges that run the length of the stem


      • Opposite, oval to strap-like (linear), prominent veins, less than 1 in. long, lack hair and no leaf stems (petioles); edges (margins) are smooth with the lower surface lined with small black dots

      • Surface covered with tiny transparent dots that can be seen by holding the leaf up to the light


        • 0.75 in. diameter; 5 yellow petals that often have tiny black dots around the edges; many stamens; clustered at tips of branches


          • Stout taproot with spreading rhizomes


            • Grows best on coarse-textured, gravelly, well-drained soils; known to occur in Elko, Lyon and Washoe counties

            • Perennial; reproduces by seed and rhizomes

            • Ingestion causes skin irritation and weight loss in white-haired animals; sometimes cultivated as a crop and used for medicinal purposes (as an antidepressant)

            • Also known as Klamath weed


              • Mowing, grazing and burning are NOT effective; a biological control agent is available Apply 2,4-D, metsulfuron or picloram to actively growing plants prior to bloom