Quick Facts

Quick facts

• St John's Wort (Hypericum perforatum) is a native Eurasian and African herb that grows up to 1.2 m high with five petal yellow flowers.
• In Australia St John's Wort invades poorly managed grazing land, open bushland, roadsides and neglected areas.
• Introduced into Australia as a garden ornament and for its medicinal uses, it is now a widespread weed of temperate Australia.
• Large and dense infestations have led to the abandonment of large areas of formally productive land in north-eastern Victoria and in New South Wales.
• Ingestion of St John's Wort can cause significant production losses and even the death of livestock.

What Does It Look Like?

What is it?

St John's Wort (Hypericum perforatum) is an erect, perennial herb that grows to about 1.2 m in height. The root system consists of a vertically-penetrating tap root and lateral roots that produce buds from which new crowns develop. The stems are often reddish in colour and bear two opposite ridges that run along the stems. The leaves are sessile (without stalks) and arranged in opposite pairs along the stem. Small translucent glands, which are especially distinctive when held up to the light, are dotted over the surface of the leaves.

The flowers are 1–2 cm in diameter and made up of five, bright yellow petals. Small, black glands may be found scattered along the edges of the petals.

The fruit is a sticky three-celled capsule that splits open from the top when mature. The fruits contain numerous, small, golden-brown seeds (1 mm long and 0.5 mm wide).

Campbell et al. (1997) studied the different leaf forms of St John's Wort that occur in Australia; these have been known as H. perforatum var. perforatum (broad leaf form) and H. perforatum var. angustifolium (narrow leaf form). They concluded that although the material differed in leaf width, other morphological differences and chemical content, they were best considered as belonging to the same variable taxon H. perforatum. However, Western Australia, and New South Wales recognise var. angustifolium as occurring in their floras. All Australian material is now referred to H. perforatum subsp. veronense.

For further information on the identification of St John's Wort, see Keith Turnbull Research Institute (2003).

For further information and assistance with identification of St John's Wort contact the herbarium in your state or territory.

Flower colour

Yellow

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

St John's Wort is found mainly in water catchment reserves and hilly, forested areas, as well as on roadsides, intermittently grazed areas, railway land, riverbanks and in pastures. When on farmland, it is mostly associated with non-arable land. It is not common on well-managed pastures, especially those with vigorous growth of improved pasture species. The most vigorous infestations occur at altitudes of approximately 600 m with an annual rainfall exceeding 760 mm. However, the plant is widespread over a range of climates, although low temperatures inhibit seed germination and seedling survival. High summer temperature also impacts negatively on the weed's performance. The plant thrives in areas that receive either winter or summer rainfall. It grows on a wide range of soils (Campbell et al. 1995).

Are there similar species?

St Peter's Wort (Hypericum tetrapterum) is a closely related species which may be confused with St John's Wort. It has similar yellow flowers and a similar habit to St John's Wort. It differs from St John's Wort as it has four ridges than run along the length of the stems. St John's Wort has only two ridges. St Peter's Wort is an uncommon weed in Australia.

Several other native and exotic species of Hypericum occur in Australia and may be mistaken for St John's Wort. Care should be taken to ensure the correct identification of suspected weeds is made before control measures are taken (see Navie 2004).

Why Is It A Weed?

What are its impacts?

St John's Wort was included in the list of 71 species that were nominated by state and territory governments for assessment as Weeds of National Significance (WONS). Following an assessment process, St John's Wort was not included as one of the 20 WONS. However, it remains a weed of potential national significance.

Agriculture: St John's Wort contains hypericin, a photodynamic compound that reacts to light, causing photosensitization (i.e. skin irritation). Hypericin also has negative effects on animal behaviour and organ function. Although St John's Wort is usually avoided by grazing animals, they will consume it when other feed is scarce. Ingestion can cause weight loss, failure to gain weight, reduced wool and milk production, and reduced reproductive performance. Some livestock will die because of grazing St John's Wort (Bourke 1997). Horses are more susceptible than other forms of livestock. For a detailed discussion on the effects of St John's Wort on animal health, see Bourke (1997).

In pastures, St John's Wort displaces useful vegetation (Campbell et al. 1995) and, if left to establish, can eliminate almost all other plants. Large and dense infestations have led to the abandonment of formerly productive areas in north-eastern Victoria and in New South Wales. It is not as problematic on arable land as continued cultivation does not allow for conditions conducive to invasion of the weed (Parsons & Cuthbertson 2001).

Native ecosystems: In summer, the masses of dry stems that are left standing can become a fire hazard (Parsons & Cuthbertson 2001). St John's Wort also invades native habitats. In these situations, its impacts are largely unknown, although it is assumed that the species would have a significant impact on native flora and fauna (Cullen et al. 1997).

Human impacts: Preparations containing St John's Wort are used medicinally, although these can affect the way some prescription medicines work. For further information, consult your doctor or for general information see the Australian Therapeutic Goods Association (http://www.tga.gov.au/docs/html/sjwinfo.htm). Fact sheets that discuss the negative impacts of St John's Wort include Naughton & Bourke (2005) and Briese et al. (2000).

How does it spread?

St John's Wort reproduces from crowns, lateral roots and seed. A mature plant can produce up to 30 000 seeds. Seed heads can adhere to the coats of livestock and seeds remain viable after being consumed by livestock. Wind may transport the seed over short distances. Water currents also spread the seed, especially where plants are in areas prone to surface run-off or in riparian habitats. Cultivation may spread the plant by scattering the root fragments. Plants also spread by the production of lateral roots which can form new crowns (Campbell et al. 1995).

What is its history in Australia?

St John's Wort was introduced to Australia as an ornamental plant and/or for medicinal purposes. Early records indicate that it was cultivated at the Melbourne Botanical Garden in 1858 and at the Adelaide Botanical Garden in 1859. It was first recorded as a weed from Bright, Victoria, in 1880. By 1905, it was widespread in Victoria and present in South Australia, Tasmania and New South Wales. Historical records along with morphological and physiological studies suggest that multiple entries and establishments have occurred across Australia (Harris & Gill 1997). The history and distribution of St John's Wort in Australia is discussed in detail by Campbell et al. (1995), Harris & Gill (1997) and Parsons & Cuthbertson (2001).

How To Manage It?

Best practice management

Non-chemical control: Land management: St John's Wort is sensitive to competition, particularly when plants are young. Good pasture management, which favours the growth of desirable species, can have significant impact on the success of St John's Wort. Overstocking encourages the weed as livestock tend to prefer other species, reducing competition.

Chemical control: Herbicides can be used in the management of St John's Wort. Numerous fact sheets and handbooks have been produced in Australia that discuss the management techniques for controlling St John's Wort. For further information on chemical, physical and biological control, see Briese et al. (2000), Parsons & Cuthbertson (2001), Bowcher (2003), Naughton & Bourke (2005), Beer & Bourke (2005), Holding (2006) and Department of Agriculture and Food (2007). Alternatively, contact the relevant weed management agency in your area.

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au.

Biological control: of St John's Wort in Australia has a long history, commencing over 80 years ago. Six biological control agents have become established in Australia. Two of these, a chrysolina leaf beetle (Chrysolina quadrigemina) and the St John's Wort Mite (Aculus hyperici), have shown potential to contribute to the control of St John's Wort (Briese 1997). See also Keith Turnbull Research Institute (1999) and Keith Turnbull Research Institute (2000) for specific information on the Chrysolina Leaf Beetle and the St John's Wort Mite respectively. For information on the potential use of fungal pathogens to control St John's Wort in Australia see McLaren et al. (1997).

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

St John's Wort plants consist of two types of stems; non-flowering stems and flowering stems. Non-flowering stems arise from the crowns in late summer and autumn and then die off in late spring. Flowering stems grow from the crown in late winter, flower in spring, die off in autumn and remain standing for several years (Campbell et al. 1995).

During spring and autumn, new crowns may be formed along lateral roots. By mid-summer, most flowers have withered but the fruits are green and still ripening. By late autumn, the flowering stems completely die off and the capsules contain ripe seed. Germination of seed occurs mainly during the warmer months, and not during winter. Seeds have been known to germinate after lying dormant in the soil for 10 years (Campbell et al. 1995). However, the vast majority of seeds germinate within the first few years of being produced (Parsons & Cuthbertson 2001).

For a detailed discussion on the growth stages and flowering of St John's Wort, see Campbell et al. (1995).

Where Is It Found?

Which states and territories is it found?

ACT, NSW, QLD, SA, TAS, VIC, WA

What areas within states and territories is it found?

The most heavily infested areas of St John's Wort are in the Central and Southern Tablelands and Slopes of New South Wales and in north-eastern Victoria (Parsons & Cuthbertson 2001). In Victoria, it is common in the drier areas of the north-east (e.g. Mansfield, Bright, Beechworth and Tallangatta) extending into the alps (e.g. Mt Clear, Mt Skene, Falls Creek area), but it is also scattered throughout the state (Walsh 1996).

It is a minor localised weed in Western Australia, where it is confined to high rainfall areas in the south-west of the state. For a comprehensive discussion about St John's Wort in Western Australia, see Dodd & Scott (1997).

In South Australia, it occurs in the Flinders Ranges, Eyre Peninsula, Northern Lofty, Murray and Southern Lofty regions (State Herbarium of South Australia 2007).

It is known to be spreading from New South Wales into southern Queensland, where there are infestations near Stanthorpe and Toowoomba (NRW 2007).

In Tasmania, it has a widespread and scattered distribution. Most Tasmanian populations are relatively small and are confined to roadsides and poorer pastures (Crane 2007, pers comm.). The distribution of St. John's Wort in Australia is discussed in detail by Campbell et al. (1995), Harris & Gill (1997) and Parsons & Cuthbertson (2001).

St John's Wort is a widespread weed in most temperate regions of the world including areas where it is native. By 1979 it was recorded as a weed in 71 countries (Holm et al. 1979).

Where does it originate?

St John's Wort is native to Europe, western Asia and North Africa (Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

ACT, NSW, TAS, VIC, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Hypericum perforatum

Other scientific names (synonyms)?

Does it have other known common name(s)?

Common St John's Wort, Perforate St John's Wort, St John's Grass, St John's Blood, Klamath Weed, Witch's Herb, Devil's Flight, Tipton Weed, Gammock, Goatsbeard, Goatweed, Herb John, Penny John, Rosin Rose, Touch and Heal