St John’s wort (Hypericum perforatum) is a toxic weed of hill and high-country pastures, especially in the South Island. The adults and larvae of St John’s wort beetles, introduced in 1943 to control the plant, defoliate plants so severely that flowering and seed production are limited. These plants have been eaten by the beetles, and still have clusters of black, shiny berries but few leaves. St John’s wort is used medicinally and in earlier times was reputed to have magical properties.
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