Common St. Johnswort (Hypericum perforatum)


Category A Weed

Sunflower family (Asteraceae)

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Stem

  • 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

    Leaves

    • 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

      Flower

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

        Root

        • Stout taproot with spreading rhizomes

          Other

          • 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

            Control

            • 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¬†

              Images

              Common St John's Wort mature plant
              Mature Plant
              Common St John's Wort Young Plant
              Young Plant
              Common St John's Wort flower
              Flower
              Common St John's Wort leaf
              Leaf
              Common St John's Wort seedling
              Seedling
              Nevada Noxious Weed Field Guide
              Nevada Noxious Weed Guide