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Hypericum tetrapterum

Description
 

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.

Distribution:

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.).

Habit:Herb
Key points:
  • St Peter's Wort (Hypericum tetrapterum) 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.
How it spreads:

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).

Where it grows:

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).

Flower colour:Yellow
Distribution map:

In Victoria see http://www.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/current_st_peters_wort 

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).

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.

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).

Origin:

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).

History:

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.

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This database is designed to provide information, including biological and ecological, on invasive plant species that are on a national weed list, or are legislated against in a state or territory. While reasonable efforts have been made to ensure the accuracy of the information, no guarantee is given, nor responsibility taken, by the Commonwealth for its accuracy, currency or completeness. The Commonwealth does not accept any responsibility for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the information contained in this database. The information contained in this database does not necessarily represent the views of the Commonwealth. This database is not intended to be a complete source of information on the matters it deals with. For further information on the images contained in the database please contact the copyright owner. All images in the weed identification tool are managed by the Australian Plant Image Index (APII). Various copyright conditions apply for these images. For further information on the copyright conditions of images contained in the database please contact the APII at: photo@anbg.gov.au.