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St. Johnswort

St. Johnswort Closeup on FlowerSt. Johnswort PlantField of St. JohnswortSt. Johnswort in Winter

(Hypericum perforatum)

Common Names

St. John's wort, common St. Johnswort, Klamath weed, common goatweed,  tipton weed

Description

This invasive is the one and same used for medicinal purposes to address depression. St. Johnswort is a perennial that can grow from one to two feet in height. This plant has a long taproot and  shallow rhizomes which extend from the root crown.  Stems are reddish in color and can be single or multiple with two opposite longitudianl ridges. Stems can branch many times towards the top of the plant. Leaves are lance-shaped, opposite on the stem, and one to two inches long with smooth margins. Each leaf contains tiny pinpoints of holes which are visible when held up to the light. Flowers are yellow and star-shaped with five petals. Tiny black dots can be found along the edges of the petals. Flowers are found in clusters at the ends of the stems and are one inch or less in diameter. Seeds are three sectioned pods filled with many dark brown seeds. Each plant can produce up to 100,000 seeds.  St. Johnswort reproduces by an aggressive root system and by seed.

Key Features

Leaves that contain tiny pinpoint holes, visible when held up to the light. Black oil glands along the margins of the yellow petals.

Habitat

St. Johnswort prefers  poor dry, gravelly,or sandy soils in full sun.  It can be found primarily in right-of-ways, roadsides, meadows, dry pastures, rangelands, fields, open woods,  waste places  and disturbed ground.

Currently found in the following counties:

Beaverhead, Carbon, Chouteau, Custer, Dawson, Flathead, Gallatin, Lake, Lewis & Clark, Lincoln, Mineral, Missoula, Park, Ravalli, Sanders, Treasure

IWM

Interesting Facts

While animals will not seek out St. Johnswort, it is toxic to livestock when consumed in quantity, especially to animals with light-colored skin.  In herbal medicine, the chemical produced by St. Johnswort is hypericin, which is the antidepressant ingredient in St. Johnswort remedies.

Visit our library for additional articles on St. Johnswort.

Photo Credits: Norman E. Rees, USDA Agricultural Research Service, Bugwood.org; Richard Old, XID Services, Inc., Bugwood.org; Carol DiSalvo, USDI National Park Service, Bugwood.org

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