St. John's wort: Introduction
R.H. Groves, CSIRO Plant Industry and Co-operative Research Centre for Weed Management Systems, GPO Box 1600, Canberra, ACT 2601, Australia.
The weed
There are more than 200 species of Hypericum (family Clusiaceae) distributed world-wide in temperate and sub-tropical regions. Of this large number of species, several have been and are still valued for their horticultural or herbal properties; it is species from these more economically significant groups that have been deliberately and widely transported and cultivated world-wide. Some species have subsequently become weedy, of which the most abundant in Australia are St. John's wort (Hypericum perforatum)and tutsan (H. androsaemum).
St. John's wort is a weed of grazing land (because it contains the alkaloid hypericin to varying extents which interferes with animal health) and/or on public land (because it may interfere with forest operations and form bright yellow infestations in late spring, thereby contributing an alien element to an-otherwise natural landscape). Whilst there are at least five European species of the genus now naturalized in southern Australia, there are also two native Hypericum spp. (viz. H. gramineum and H. japonicum) that are far less obvious in the natural landscape; the distribution of H. gramineum is as widespread as and may overlap with that of its weedy introduced congeners.
Plant Protection Quarterly (1997) 12 (2) 51-52.