Quick Facts

Quick facts

  • St Peter's Wort (Hypericum tetrapterum), a native of Eurasia and Africa, is herb with yellow flowers that grows to 1 m high
  • It is primarily a weed of riparian areas such as along gullies and streams, but also capable of invading wet pastures.
  • Currently there are relatively few infestations in Australia. It is only known to be naturalised in Tasmania and Victoria.
  • It is thought to be poisonous to stock.
  • St Peter's Wort is one of seventeen sleeper weeds identified by the Bureau of Rural Sciences which could have significant impact on agriculture if allowed to spread.

What Does It Look Like?

What is it?

St Peter's Wort (Hypericum tetrapterum) is an erect perennial herb that grows to 1 m high. The stems are square in cross-section, have prominent wings that run along each stem angle, are hairless, green to reddish-brown in colour and marked with small, black glands. Vegetative spread of the plant is facilitated by the production of roots from the lower nodes of the stems. Its leaves (up to 3 cm long and up to 2 cm wide) are light-green in colour, and occur in opposite pairs along the stems. The surfaces of the leaves are prominently veined (reminiscent of the leaves of common mint) and are scattered with numerous, translucent glands. Sometimes very small, black glands occur on the edges of the leaves.

The flowers of St Peter's Wort are yellow (up to 1.2 cm diameter) and grouped together in dense clusters at the ends of the branches. The petals, of which there are five, often have small, black glands along their edges.

The fruit is a 3-celled, ovoid capsule, 5–10 mm long and contains many small, brown seeds, each 1–1.5 mm long (Parsons & Cuthbertson 2001; Navie 2004).

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

Flower colour


Growth form (weed type/habit)


Where it currently grows? Preferred habitat

St Peter's Wort prefers a temperate climate and is strongly associated with riparian habitats such as the banks of waterways, in swamps and wet pastures (Stace 1991; Parsons & Cuthbertson 2001; Navie 2004).

Are there similar species?

St John's Wort (Hypericum perforatum) is a closely related species which may be confused with St Peter's Wort (Hypericum tetrapterum). It has similar yellow flowers and a similar habit to St Peter's Wort. It differs from St Peter's Wort as it has only two feint ridges than run along the length of the stems. St Peter's Wort has four conspicuous ridges.  St John's wort is a widespread and much more significant weed in Australia. Several other native and exotic species of Hypericum occur in Australia and may be mistaken for St Peter's Wort (Navie 2004). Care should be taken to ensure the correct identification of suspected weeds is made before control measures are taken.

Why Is It A Weed?

What are its impacts?

St Peter's Wort is one of seventeen sleeper weeds identified by the Bureau of Rural Sciences (following consultation with the Australian Weeds Committee) which could have nationally significant impacts on agriculture if allowed to spread.

St Peter's Wort is thought to be poisonous to stock and cause toxicity problems in the same manner as St John's Wort (Hypericum perforatum). However, cases of St Peter's Wort poisoning have not been recorded in Australia (Parsons & Cuthbertson 2001).

Agriculture: It is capable of forming dense populations especially on the banks of water courses and may encroach into moist pasture and grassland (Parsons & Cuthbertson 2001). It is not yet as extensively naturalised or as aggressive as the related Tutsan (Hypericum androsaemum) and St John's Wort, although, without management has the potential to become more problematic (Muyt 2002). Whilst unlikely to establish in regularly cultivated areas, it has demonstrated a capacity to invade pasture in southern Tasmania. Whilst this effect is likely to be limited to poorly maintained pastures, the consequence of land owners failing to control the plant would include a larger source of seed for potential distribution to natural areas.

Native ecosystems: St Peter's Wort is not commonly described as invasive in natural environments but may displace native riparian species in disturbed situations. Groves et al. (2003) lists it as an environmental weed. It is recorded as a potential threat to one or more native vegetation formations in Victoria (Carr et al. 1992).

How does it spread?

Because St Peter's Wort is associated with riparian habitats, its dispersal is most often via the movement of seeds in water. Other vectors for spread include the movement of soil contaminated with seeds and rhizomes Spread may also be assisted by soiled vehicles, equipment and animals. Spread also occurs over short distances by the growth of rhizomes and by the layering of stems (Parsons & Cuthbertson 2001; Issac 2003; Navie 2004).

What is its history in Australia?

Early records of St Peter's Wort include a listing in an 1865 catalogue of plants grown in the Royal Society's Garden in Hobart (now Royal Tasmanian Botanical Gardens). It was first recorded in Victoria in 1920 and as naturalised in 1965 (Parsons & Cuthbertson 2001). Records held by the Tasmanian Herbarium indicate that it was first recorded as naturalised in Tasmania in 1982.

How To Manage It?

Best practice management

Non-chemical control: Land management: Cultivation is effective in controlling St Peter's Wort but it must be implemented thoroughly to minimise regrowth. Good pasture management enables competition from pastures to inhibit seedlings and regrowth.

Chemical control: Herbicides have been effective in controlling this weed (Parsons & Cuthbertson 2001).

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

Does it have a biological control agent?


When does it grow? (lifecycle/growth calendar)

The life cycle of St Peter's Wort is similar to that of St John's wort (Hypericum perforatum). Seeds germinate in autumn, winter or spring and plants continue to grow without flowering in the first year. Erect woody stems are produced in the spring following germination. Flowering starts in November and continues through to February. Flowering stems die in late summer (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?


What areas within states and territories is it found?

St Peter's Wort is not currently widespread and only known from sites in Victoria and Tasmania. In Victoria, St Peter's Wort has been recorded along the Woori Yallock Creek, the foothills of the Dandenong Ranges to the east of Melbourne, but is also known to occur along several other creeks in the Yarra and Diamond Valleys (Issac 2003). In Tasmania, it is known to occur at several sites south of Hobart in the Huon Valley. The largest population consisting of 500 or more plants is on a wet river flat beside the Huon River at Huonville (DPIW 2006; Baker 2007, pers. comm.).

Where does it originate?

St Peter's Wort is a native of Europe, western Asia and northern Africa (Navie 2004). It is frequent throughout the British Isles except for northern Scotland (Stace 1991).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?


Where is it a declared weed?


Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?


Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?


Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Hypericum tetrapterum

Other scientific names (synonyms)?


Does it have other known common name(s)?

Square Stemmed Hypericum, Square Stemmed St John's Wort, Square-stalked St. John's Wort, Winged St John's Wort, European Perennial St John's Wort

Blackberry – a community-driven approach in Victoria

Blackberry the weed (Rubus fruticosus aggregate) was first introduced to Australia by European settlers in the mid-1800s as a fruit. It was recognised as a weed by mid-1880s. Blackberry is a serious issue across Australia. It is estimated that blackberry infests approximately 8.8 million hectares of land at an estimated cost of $103 million in annual control and production losses.

Read Case Study