Square-Stemmed St John's Wort

What is square-stemmed St John's wort?

(Hypericum tetrapterum)

Square stemmed St Johns wort, photo: John Crellin Generic Weed Distribution Map
  • Square-stemmed St John's wort has the potential to become a significant riparian (river-side) weed in Tasmania.
  • Square-stemmed St John's wort is a declared weed in Tasmania under the Tasmanian Weed Management Act 1999. The importation, sale and distribution of square-stemmed St John's wort are prohibited in Tasmania.


How to identify square-stemmed St John's wort

  • Square-stemmed St John's wort is an erect perennial (long-lived) herb growing to 1 metre high. Square-stemmed St John's wort is similar to St John's wort, however the reddish stems are almost square in cross-section.
  • The leaves are stem-clasping at the base and have numerous small oil glands that give the leaf a perforated appearance when held up to the light. The flowers are bright yellow with black glands dotted along the margins of the petals, and grow in small dense clusters at the end of the branches. The fruit is a sticky capsule containing numerous, light brown cylindrical seeds.
  • Germination occurs mainly in autumn after rain. Flowering occurs from spring through summer. The woody stems die back after flowering but may remain standing for months to years.
  • The rootstock or woody crown produces numerous horizontal rhizomes (underground stems) just below the surface; these rhizomes produce buds from which new above-ground growths develop each year in spring.

Square stemmed St Johns wort, photo: John Crellin
Image top: Square-stemmed St John's wort, photo: John Crellin
Image above: Square-stemmed St John's wort in flower, photo: John Crellin


Square-stemmed St John's wort in Tasmania

  • Square-stemmed St John's wort occurs at several locations in the Huon Valley in southern Tasmania (see map). All populations are relatively small.
  • Square-stemmed St John's wort occurs adjacent to streams and swamps from where it encroaches into moist pastures and riparian (river-side) vegetation. Square-stemmed St John's wort forms very dense stands and appears to be as strongly competitive as St John's wort.


What is the legal status of square-stemmed St John's wort in your area?

Detailed management and control guidelines for square-stemmed St John's wort can be found in the Square-Stemmed St John's Wort Control Guide. Refer also to Herbicides for Square-Stemmed St John's Wort Control. For further information see DPIPWE's Weed Links and Resources.

See also
Square-Stemmed St John's Wort Control Guide
Herbicides for Square-Stemmed St John's Wort Control
Statutory Management Plan for Square-Stemmed St John's Wort
Weed Links and Resources

Other useful links
Pest Genie
APVMA

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