Australia > All Weeds > St John's Wort

St John's Wort

Hypericum perforatum

Origin: Native of Europe, western Asia, North Africa.


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Flowering specimen, Penrith, NSW

Family: Clusiaceae.

Known Hazards: Skin contact with the sap, or ingestion of the plant, can cause photosensitivity in some people.

Habitat: Open woods, hedgebanks and grassland, in dry sunny places, usually on calcareous soils.

Edibility Rating: 2 (1-5)

Medicinal Rating: 4 (1-5)

Physical Characteristics: Perennial rhizomatous herb with erect stems to 1.2 m high. Leaves hairless, paler on the lower surface, ovate to narrow-oblong to about 3 cm long. Stems with opposite weakly pronounced longitudinal ridges and with occasional black glands. Fruit sticky, containing many pitted seeds about 1 mm long. Roots to 1 m deep; rhizomes shallow producing many buds.
Flowers: About 2 cm wide with 5 bright yellow petals. Flowers late spring and summer. The flowers are hermaphrodite (has both male and female organs) and are pollinated by Bees, flies. The plant is self-fertile.

Distinguishing features: Distinguished by numerous translucent glands on the leaves (obvious when leaves are held to the light), and yellow flowers often with black glands on the petal margins (look like dots—see photo).

Dispersal: Spread by seed, growth of rhizomes and movement of cut sections of rhizomes.

Edible Uses

The herb and the fruit are sometimes used as a tea substitute. The flowers can be used in making mead

Medicinal Uses

Analgesic; Antiseptic; Antispasmodic; Aromatic; Aromatic; Astringent; Cholagogue; Digestive; Diuretic; Expectorant; Homeopathy; Nervine; Resolvent; Sedative; Stimulant; Vermifuge; Vulnerary. St. John's wort has a long history of herbal use. It fell out of favour in the nineteenth century but recent research has brought it back to prominence as an extremely valuable remedy for nervous problems. In clinical trials about 67% of patients with mild to moderate depression improved when taking this plant. The flowers and leaves are analgesic, antiseptic, antispasmodic, aromatic, astringent, cholagogue, digestive, diuretic, expectorant, nervine, resolvent, sedative, stimulant, vermifuge and vulnerary. The herb is used in treating a wide range of disorders, including pulmonary complaints, bladder problems, diarrhoea and nervous depression. It is also very effectual in treating overnight incontinence of urine in children. Externally, it is used in poultices to dispel herd tumours, caked breasts, bruising etc. The flowering shoots are harvested in early summer and dried for later use. Use the plant with caution and do not prescribe it for patients with chronic depression. The plant was used to procure an abortion by some native North Americans, so it is best not used by pregnant women. See also the notes above on toxicity. A tea or tincture of the fresh flowers is a popular treatment for external ulcers, burns, wounds (especially those with severed nerve tissue), sores, bruises, cramps etc. An infusion of the flowers in olive oil is applied externally to wounds, sores, ulcers, swellings, rheumatism etc. It is also valued in the treatment of sunburn and as a cosmetic preparation to the skin. The plant contains many biologically active compounds including rutin, pectin, choline, sitosterol, hypericin and pseudohypericin. These last two compounds have been shown to have potent anti-retroviral activity without serious side effects and they are being researched in the treatment of AIDS. A homeopathic remedy is made from the fresh whole flowering plant. It is used in the treatment of injuries, bites, stings etc and is said to be the first remedy to consider when nerve-rich areas such as the spine, eyes, fingers etc are injured.

Other Uses

Dye; Tannin. Yellow, gold and brown dyes are obtained from the flowers and leaves. A red is obtained from the flowers after acidification. A red dye is obtained from the whole plant when infused in oil or alcohol. A yellow is obtained when it is infused in water. The plant is said to contain good quantities of tannin, though exact figures are not available.

Notes: There are two varieties, var. perforatum with broad leaves and var. angustifolium with narrow leaves but intermediates are also common. One plant will produce thousands of seeds and these may remain viable in the soil for many years. Introduced to Australia in 1800s, and still spreading, especially on roadsides and cleared land. Major weed in USA and Canada. In Australia biocontrol has been partly successful but work is still continuing. Hypericin is concentrated in oil glands and causes photosensitisation in light skinned stock especially sheep.


Flower detail by Wikispecies

Torino, Italy


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