St John's Wort

Hypericum perforatum L.

Family: - Clusiaceae.


Hypericum is from the Greek hyper meaning above and eikon meaning image or picture because it was hung above religious pictures to ward off the devil, who in response punctured the leaves with a needle.

Perforatum refers to the perforated appearance of the leaves.

St Johns Wort may be derived from St John's Blood, the name of the pigment extracted from the petals; or because it flowers in Europe close to St John's day on the 24th June; or because it was associated with the Knights of St John; or because it was hung on St John's eve to ward of evil spirits. Wort is from the Old English wyrt meaning a medicinal herb or plant.

Other names:

Common St John's Wort

Goat weed (USA)

Klamath weed (USA)

Perforate St John's Wart (UK)

Racecourse Weed because one of the first infestations escaped from a garden in Bright, NSW and overran a racecourse.

Witch's herb.


Erect, about 700 mm tall perennial herb or small shrub with sprays of golden yellow, 5 petalled, 20 mm round, daisy like flowers in spring and early summer. It also reproduces from rhizomes and persistent rootstocks. The leaves are opposite, light green with many translucent oil glands





There are 2 forms - a broad leaf type from northern Europe and a narrow leaf type from the Mediterranean.

Paired, opposite. Have a curry smell when crushed.

Stipules - Absent.

Petiole - None.

Blade - Pale to yellowish green and lighter underneath, oval to parallel sided or oblong, 10-30 mm long, and variable width, with numerous oil glands which appear as black or translucent spots when the leaf is held up to the light. The black dots tend to occur on the lower surface. Tip acute or obtuse. Smooth edges. Hairless. Narrower towards the base.


Barren stems spindly and low lying, several emerging from the crown. Flowering stems, often reddish, rigid, woody at the base, erect, 600-1200 mm long, several emerging form the crown, 2 opposite lengthwise ridges from the base of the leaves and bearing dark glands. They branch mainly from the top with many short lateral branches. Top branches are at approximately 45 degrees from the main stem. Hairless.

An extensive rhizome system creeps just below the soil surface.

Flower head:

Dense clusters on the end of the stems in leafy, broad, cymose corymbs.


Golden yellow, many, 15-25 mm in diameter, regular, bisexual.

Ovary - superior, 3 celled. 3, free, persistent styles with terminal stigmas.

Sepals - 5, overlapping, free, lance shaped, 4-5 mm long, dotted with glands. Pointed tip. Persistent. Sepals of young buds often have reddish markings especially near the tips.

Petals - Five, twisted, yellow with black dots along the edges, twice as long as sepals.

Stamens - 50-100, in 3 bundles. Yellow, Thread like filaments.

Anthers - Sub globular with a small gland at the top.


Sticky, 3 celled, many seeded, capsule, 5-10 mm long, twice as long as the sepals with 3 persistent styles as long as the fruit. Many raised, oblique, parallel sided glands.


Golden brown to black, pitted, 1 mm long, oblong with rounded ends.


Stout main roots to 1000 mm deep and creeping rhizomes just below the surface that produce buds and new shoots each year.

Key Characters:

Yellow petals with black dots, twice as long as sepals. Capsule striped and long. Stamens in 3 bundles.


Life cycle:

Perennial. The plant reproduces from seed and vegetatively from underground rhizomes. Seeds germinate in the warmer months from October to March. They tend to remain vegetative and flower in their second season. Flowering stems emerge in spring, grow vigorously, and flower in summer. The fruit capsule matures, the flowers turn brown and the leaves turn yellow in autumn as new shoots appear at the base of the plant. The old stems die off over winter but may remain standing for several months. Established plants have 2 types of growth. Autumn and winter stems are spindly, spreading or prostrate and leafy. Spring stems are erect, woody and bear flowers then die off, but remain standing for many months. This gives infestations a grey appearance from a distance. Seeds do not germinate until an inhibitor in the capsule is broken down. Its growth can be quite variable depending on seasonal conditions.


It does not persist in shaded situations.


By seeds, crowns and rhizomes.

Flowering times:

November to February in SA.

Late spring to early summer in western NSW.

Spring and early summer or November to February in WA.

Flowering times are variable and depend on the season.

Seed Biology and Germination:

The capsule contains a germination inhibitor that prevents seeds germinating for 4-6 months.

High temperatures of 100-1400C increase germination and large germinations often occur after fires.

Most seed germinates in the first few seasons.

Some seeds remain dormant for at least 20 years.

Vegetative Propagules:

Buds on the rhizome.

Regeneration from a perennial rootstock is common.


Several varieties exist.

The angustifolium variety is the most common in Australia and has narrower leaves than common European varieties.

Several separate introductions have occurred.


Population Dynamics and Dispersal:

The main spread is by seed which is readily carried by water, soil, animals and agricultural produce especially hay and chaff. The sticky seed capsules freely attaches to wool, fur, clothing and bags. The fine seed passes through animals unaffected.

Local spread is mainly by extension of the creeping rhizome and by cultivation which moves rhizome fragments.

Each plant may produce 33,000 seeds.

Prostrate and leafy autumn stems form a thick mat that smothers companion plants.

It is an early coloniser of disturbed sites (Groves, 1997).

It is spread in fodder, by stock and intentional plantings in gardens.

Low levels of disturbance favour it whereas high levels of cultivation virtually eliminate it.

It spread at 2 km/year initially in Vic.

Spread by rhizomes is about 300 mm year.

Spread of seed by wind is around 10 m/year.

Spread in water is probably due to whole plants or soil moving in floods because the seed is not buoyant.

Spread by capsules adhering to stock and native and feral animals is the most probable cause of the observed rates of spread.

Transport in cereal grain, hay and intentional planting of the seed is probably mainly responsible for long distance dispersal.

Movement in faeces, soil on machinery, animals and pine seedlings have also been reported as responsible for spread.

In continuous wheat systems it builds up quickly, whilst under the more heavily cultivated tobacco production system it disappears.

Moore and Cashmore (1942) showed productions figures for St John's Wort of 270 kg/ha for grazed land, 780 kg/ha on land ploughed once and 980 kg/ha on land that was mown, burnt then scarified.

Origin and History:

Europe and the Mediterranean. Western Asia. North Africa.

There are 2 forms in Australia - a broad leaf type from northern Europe and a narrow leaf type from the Mediterranean.

Contaminated vetch seed from Australia led to infestations in South Africa in 1942.

First recorded in Melbourne Botanic Gardens in 1857 and Adelaide Botanic Gardens in 1859. It was in Tasmania by 1865. It was in WA by 1934 and probably imported in feed for oxen or horses around 1900 (Dodd and Scott, 1997).

The first outbreaks were at Bright in Victoria in 1880, the Coromandel Valley in SA around 1881 and Mudgee in NSW in 1890 (Harris and Gill 1997).

By 1900 it was in NSW, SA and WA.

The only infestation in Queensland has been eradicated.



Commonly found in the north-west and patches also in the north, north Midlands, south and probably other parts of Tasmania but no large infestations have been recorded.

It infests 200,000 ha in NSW (Freebairn, 1986) and 175,000 ha in Victoria of which 12,000 ha is agricultural land (Shepherd, 1983). The area infesting agricultural land in Vic doesn't appear to have increased much since 1916 (Harris and Gill, 1997).

Small areas occur in WA and are controlled. The area infested in WA has remained fairly constant at 200-300 ha over the last 50 years (Dodd and Scott, 1997).



Humid and sub humid temperate.

Most abundant in areas with an annual rainfall greater than 750 mm and elevations up to 500-1000 m.

In WA it is restricted to areas with annual rainfall greater than 400 mm.


Prefers untilled but loose soils.

Plant Associations:


In California it is the single greatest cause of financial loss on the range lands before the introduction of biocontrol insects.


Used as an antidepressant in herbal medicine. Most prescribed antidepressant in Germany. Hypericin appears to be the active ingredient.

It is grown commercially in Poland for oils for the cosmetic industry.

Used in herbal medicine to induce abortion, bed wetting, burns, congestion, dysentery, gout, insomnia, nervous disorders, parasites, rashes, rheumatism, urinary problems and wounds,

Used in folk lore to ward off evil spirits and bring good luck.

Source of red and yellow dyes.

Used in distilling vodka.

Herbal tea for melancholy.



Weed of roadsides, stock routes, disturbed areas, wood lands, national parks, water catchment areas and invasive in pasture.

It is very competitive often excludes all other species where it establishes in the absence of biocontrol agents.

Fire hazard in plantations.

Relatively unpalatable.

Taints milk.

Affects fleece quality and causes vegetable fault.



Toxic to horses, sheep, cattle and goats. Horses are most sensitive and goats least sensitive. Animals with coloured skin are less sensitive to toxicity than those with white skin.

Causes photo-sensitisation in animals and when stock come in contact with water, eg dipping or crossing streams, they struggle violently and may drown.

Causes contact dermatitis in people.

Green and dry plants and hay can be toxic.

The toxic substance is a fluorescent red pigment called hypericin and is concentrated in the oil glands in the leaves and flowers.

Most field cases occur when other feed is scarce, St John's Wort is young and stock are not accustomed to it.

Both leaves and flowers may be toxic.


Photo-sensitisation that is only apparent in bright light. It affects areas of skin not protected by the coat or pigment.

Shaking of the head, restlessness, itching, frenzy, sensitivity to touching and water, biting or rubbing of exposed areas causing damage especially of the ears, reddening and swelling of exposed areas, droopy ears, oozing, death of skin, infection and scab formation. The ends of the ears may become brittle and snap off. Tenderness of the mouth may stop the animal grazing.

Madness on contact with water.

Sheep may become blind.

Some may abort, lose condition, lose milk production, convulse and die.


Remove stock from the infestation and shift to a shady area. Recovery is normally expected.

Provide alternative feed.


Noxious weed of ACT, NSW, TAS, VIC, WA.

Management and Control:

In extensive infestations, the most profitable control is to encourage competitive pastures, fertilise appropriately and introduce the Chrysolina beetle. Control rabbits in areas where they are causing overgrazing.

It rarely persists on cultivated crop land.

Scattered infestations can be controlled by grazing with goats because they are less sensitive to poisoning and find it more palatable than other stock. Dark skinned sheep and cattle have also been used to control it by grazing.

If grazing with merino sheep the following is suggested by Bourke and Cambell of NSW Agriculture. Use sheep from a fine wool bloodline, don't use pregnant or lactating sheep, use adult sheep with at least 4 months wool, Graze broadleaf wort from May 1 to October 14 and narrow leaf wort from July 1 to September 14 in the first year and increase the time as the levels fall in subsequent years. Remove sheep during spring before flower spikes reach 50-100 mm tall to avoid high toxin levels.

Planting infested pastures to pines also controls it. However, it quickly returns when the trees are cut down.


Eradication strategies:

Treat small areas with Tordon or Grazon. 2,4-D is most effective on actively growing plants, before flowering and about 450 mm tall. Glyphosate is effective on flowering plants.

A combination of the Chrysolina beetle and pasture improvement using Subterranean Clover and Phalaris has led to the elimination of St John's Wort in many agricultural situations. Infested areas should be ploughed in summer to expose and desiccate rhizomes. Reworked in Autumn. Planted to pasture, fertilised, lightly grazed or spray grazed with 2,4-DB and normally grazed in following years. Stock may be poisoned in dense infestations. Goats are the preferred grazing animal because they are less likely to be poisoned and find it more palatable than other stock. Over grazing should be avoided.

In open timbered areas control is difficult. In dense plantations it usually disappears but returns when the area is logged. Rabbit infestations should be controlled because they selectively graze plants that compete with St Johns Wort.

Herbicide resistance:

Biological Control:

3 beetles, 2 moths, an aphid and a mite have been released to try and control St Johns Wort.

Chrysolina hyperici beetle was introduced in the early 1930's for control. Chrysolina quadrigemina and Agrilus hyperici beetles and Zeuxidiplosis giardi gall midge were introduced and established later. Chrysolina provides good control in open areas but not in shaded forest areas. Control is often poor in some areas where summer rainfall assists the recovery of the weed.

Aculus hyperici, a mite appears to have some potential for control at present.

Related plants:

Tutsan (Hypericum androsaemum) has broad egg shaped leaves and is weedy in Australia.

Rose of Sharon (Hypericum calicinum)

Small St Johns Wort (Hypericum gramineum) has much finer leaves, is widely distributed and is an Australian native plant.

Matted St Johns Wort (Hypericum japonicum) has much finer leaves and is an Australian native plant.

St Peters Wort (Hypericum tetrapterum)

Tangled Hypericum (Hypericum triquetrifolium)

Hypericum x moserianum has narrow egg shaped leaves.

Plants of similar appearance:


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Freebairn, (1986). quoted in Harris and Gill (1997).

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Harris and Gill (1997).History of the introduction and spread of St John's Wort (Hypericum perforatum L.) in Australia. Plant Protection Quarterly 12(2):52-56.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P134. Photo.

Hyde-Wyatt, B.H. and Morris, D.I. (1980) The Noxious and Secondary Weeds of Tasmania. (Tasmanian Department of Agriculture, Hobart, Tasmania). P77. Diagram.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #670.5.

McBarron, E.J. (1983). Poisonous plants. (Inkata Press, Melbourne). P98. Diagram.

Meadly, G.R.W. (1965). Weeds of Western Australia. (Department of Agriculture - Western Australia). P110-112. Diagrams. Photo.

Moore and Cashmore (1942). quoted in Harris and Gill (1997).

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious weeds of Australia. (Inkata Press, Melbourne). P387-391. Photos.

Shepherd, (1983). quoted in Harris and Gill (1997).


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