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Square-stemmed St John's wort (Hypericum tetrapterum)

This introduced perennial is naturalised in parts of Tasmania and southern Victoria, where it is regarded as an environmental weed. It can form dense stands in moist, streamside vegetation and compete strongly with native plants.

Key facts

Type: Weed, herb.

Native to: North-western Africa, Europe and western Asia.

Established in: VIC, TAS.

Other names: St. Peter's wort, European perennial St John's wort, Square-stalked St. John's wort, Winged St John's wort.

Best time to act: Look for plants when they are flowering in late spring and summer, and aim to treat them before seed capsules mature.

Identification

  • An upright perennial herb with opposite leaves and conspicuous, narrow wings running along its four-angled stems.
  • Leaves are unstalked and oval to lance-shaped, with small translucent glands that may be visible when held to the light.
  • Bright yellow, five-petalled flowers grow in clusters at the ends of stems.
  • After flowering, the plant forms small capsules containing seeds.
  • Look-alike: St John's wort (Hypericum perforatum) also has yellow flowers and opposite leaves, but its stems usually have two raised lines rather than four prominent wings.

Where it grows

In Australia it is most concerning in moist places, especially stream and swamp margins and other riparian areas in temperate regions.

Why it matters

  • Dense stands can dominate riparian vegetation and compete strongly with native plants.
  • It is regarded as an environmental weed in Victoria and Tasmania and is considered a potential threat to vegetation communities in Victoria.

How it spreads

  • It reproduces by seed, and established plants can also spread vegetatively from rhizomes.
  • Seeds and plant material may be moved in soil, water or on contaminated equipment.

Control options

  • For small infestations, carefully dig out plants and as much of the root and rhizome system as possible, taking care not to leave fragments behind.
  • Contain and dispose of flowering or fruiting material so it cannot spread; follow local guidance for disposal.
  • For larger infestations, use only herbicides registered for the site and situation, follow the label, and take particular care near waterways.
  • Check treated areas repeatedly for regrowth and seedlings, and seek advice from the relevant state biosecurity agency about local reporting or control requirements.

Hygiene and washdown

  • Clean soil and plant material from boots, tools, vehicles and machinery before leaving an infested site, and avoid moving contaminated soil or vegetation.
  • Inspect and clean vehicles, plant and footwear before leaving an infested area, paying attention to tyres, radiators, belly plates, tracks and floor mats.
  • Wash down at a designated bay where runoff is contained and can be monitored for seedlings.
  • Record each washdown so the client has evidence of clean entry and exit.

Classification by state

  • Australia (national): No national listing. Managed under state and territory law.
  • Queensland: Not prohibited or restricted. Not listed as prohibited or restricted matter in Queensland. Everyone must also take all reasonable and practical steps to minimise its risks (the general biosecurity obligation).
  • New South Wales: Not a priority weed. Not a state or regional priority weed in NSW. The general biosecurity duty applies: anyone dealing with it must prevent, eliminate or minimise the risk it poses.
  • Victoria: Regionally controlled / restricted weed (varies by region). Where it is regionally controlled, landowners must take all reasonable steps to prevent its growth and spread on their land. Where it is a restricted weed, trade in it (including the plant, its seed or contaminated material) is prohibited.
  • South Australia: Not declared. Not declared under the Landscape South Australia Act 2019. Other laws may still apply.
  • Western Australia: Not listed. Not found in the Western Australian Organism List. Check with DPIRD before moving or keeping it.
  • Tasmania: Declared weed. Property managers are required by law to control declared weeds, and their import and sale are prohibited.
  • Northern Territory: Not declared. Not on the NT A to Z weed list, and Weeds Australia does not list it as declared in the NT. Check the NT declared weeds list before moving or planting it.
  • Australian Capital Territory: Not declared. Not declared under the Biosecurity Act 2023 (ACT). A general biosecurity duty still applies.

Legal obligations

Every state and territory places a duty on landholders and people working on land to prevent the spread of invasive species, such as the general biosecurity obligation in Queensland and the general biosecurity duty in New South Wales. Declarations and control requirements differ between states and local government areas, so check the current official list before work starts.

  • Victoria: Catchment and Land Protection Act 1994 (Vic), administered by Agriculture Victoria
  • Tasmania: Biosecurity Act 2019 (Tas), administered by Biosecurity Tasmania

Sources