Floridata Plant Encyclopedia

A Floridata Plant Profile 913 Hypericum perforatum

Common Names: St. John's wort, perforate St. John's wort, Klamath weed, goat weed Family: Hypericaceae (St. John's wort Family)

St John's wort
This St. John's wort shares space in Steve's vegetable garden next to fennel (Foeniculum vulgare) and garlic (Allium sativum).


Hypericum perforatum is a short lived herbaceous or semiwoody perennial sub-shrub that grows in an open, bushy clump up to 2-3 ft (0.6-1.2 cm) tall and 2 ft (0.6 m) across. It spreads by runners and by profuse seeding. The stems have two raised ridges along them and are woody at their bases. Perforate St. John's wort has opposite leaves that are oval and a little over 1 in (2.5 cm) long. The leaves are scattered with translucent dots that, when viewed from the underside (a hand lens may be necessary), look like little round holes that go all the way through the leaf. Actually these are oil-filled glands, and this is a characteristic common to nearly all of the hundreds of species of Hypericum.

Perforate St. John's wort blooms profusely throughout the summer and fall, producing clusters of bright yellow star shaped flowers. The flowers, about 1 in (2.5 cm) across, have five black-dotted petals and many prominent yellow stamens which collectively look like fine bristles of a brush. The foliage has a peculiar, distinctive odor and a bitter taste. When crushed, the flower petals may exude a red-colored oil.

Var. angustifolium has narrow leaves and smaller flowers; var. latifolium has broader leaves and larger flowers; and var. microphyllum has smaller leaves and smaller flowers.


Hypericum perforatum is native to much of Europe, northern Africa and western Asia. It has escaped cultivation and become established in many other parts of the world, especially Australia and the US. In some places it has become a pernicious weed, invading pastures, road shoulders and open lands. Eradication efforts in the US have included extensive herbicide applications and the release of an Australian beetle that eats the plant. The beetle proved effective.


Light: Full sun to part shade. Moisture: Regular garden watering. Hardiness: USDA Zones 3 - 8. Propagation: Perforate St. John's wort is easily grown from seed and will usually self sow without any help from the gardener. Also, the roots can be divided to start new plants.


Use perforate St. John's worts in a perennial border or in a rock garden. This and most of the St. John's worts are ideal subshrubs for the natural garden. Like most species in the genus, this one blooms over a long period and can be expected to self sow.

St. John's wort
St. John's wort has small oval leaves that are held oppositely on the stem and are covered with translucent glands that appear to be tiny holes.


Centuries ago, Europeans hung St. John's wort in windows and above images to protect from evil spirits. The generic name, Hypericum, comes from the Greek for "above an icon." Traditionally, St. John's wort leaves and flowers were gathered on St. John's Day (June 24th - the birthday of John the Baptist), and made into a tonic used to protect the eyes and to guard against all those evil spirits. The specific part of the name, perforata refers to the translucent glands in the leaves that look like perforations. The word "wort" means simply "plant" and is a part of many plant names.

There are more than 400 species of Hypericum, occurring throughout the temperate regions of the world in all types of habitats. Many of the American species make handsome garden ornamentals. Some authorities do not recognize the family, Hypericaceae, and instead include all the St. John's worts in the Clusiaceae, the mangosteen family.

Extracts from the leaves and flowers of perforate St. John's Wort have been proven useful in treating mild depression, anxiety and insomnia. The active ingredient, hypericin, seems to influence brain levels of dopamine and norepinephrine, and may inhibit activity of the neurotransmitter, serotonin. Hypericin also has been shown to have antibacterial and antiviral properties. Hypericin currently is being investigated as a treatment for several bacterial diseases, including tuberculosis, and for several viral diseases, including the HIV and herpes simplex viruses.

In most of the western world, St. John's wort is taken internally for depression, and externally for wounds and other skin disorders. St. John's wort is an ingredient in the traditional Russian soft drink, Baikal. In Germany, St. John's wort is the most popular prescription drug for treatment of depression. In the US, St. John's wort is not considered a prescription drug, but sold as a dietary supplement, for which health-benefit claims cannot legally be made.


Perforate St. John's wort is listed by the California Department of Food and Agriculture as a noxious weed that is now so widespread that the department does not endorse government funded control efforts except in nurseries or seed lots. It also is listed by the California Exotic Pest Plant Council as an invasive weed.

It has been reported that consuming large amounts of St. John's wort or its extracts can cause increased photosensitivity and dermatitis in some people. Floridata does not advocate the medicinal use of any plant, and makes no claims regarding the effectiveness of any herbal remedies.

Steve Christman 2/9/01; updated 10/17/03

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Hypericum species profiled on Floridata:

Hypericum calycinum

( Aaron's beard, creeping St. John's wort, Rose of Sharon, goldflower )

Hypericum frondosum

( golden St. John's wort, blueleaf St. John's wort, cedarglade , St.John's wort )

Hypericum perforatum

( St. John's wort, perforate St. John's wort, Klamath weed, goat weed )

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