St John’s wort
Clusiaceae (St John’s wort)
Also known as
Goatweed, Klamath weed, Mother Cameron’s weed
Where is it originally from?
Europe, West Asia, North Africa
What does it look like?
Hairless perennial herb (<1 m tall), with roots with slender, creeping rhizomes. Erect stems emerge singly or severally from base, and are round with two ridges, woody at base, with upper branches in opposite pairs at 45 degrees. Narrow to oval leaves (10-27 x 1-8 mm) are in opposite pairs along the stems, stalkless and covered with many translucent glandular dots. Flat-topped clusters made up of many golden-yellow, star-like flowers (8-20 mm diameter, Dec-May) with 5 black-dotted petals are produced on the ends of stems, followed by seeds. Stems usually die in autumn, leaving prostrate, barren, leafy shoots, often forming dense mats.
Are there any similar species?
There are many other closely related Hypericum species, five exotic species that have been found in the wild and two native species (both of which lack black glandular dots, and are low growing or mat forming).
Why is it weedy?
Quick maturing, relatively long-lived, produces many long-lived seeds and a tough rhizome system, and forms dense stands or mats. Tolerates cold to hot temperatures, damp to drought conditions, wind and damage, but is intolerant of shade. Poisonous, so stock tend to avoid it.
How does it spread?
Seeds spread by wind (minor), and possibly livestock. Rhizomes spread by soil and water movement and greenwaste dumping. Sources of seed and rhizomes for new infestations include roadsides, pasture, wasteland, riverbeds and gardens. Increasingly cultivated as a medicinal herb.
What damage does it do?
Displaces vulnerable herb and tussock species.
Which habitats is it likely to invade?
Disturbed short tussockland, herbfields, bare land, and open spaces throughout New Zealand.
What can I do to get rid of it?
1. Spray (spring-summer only): glyphosate (10ml/L) or metsulfuron-methyl 600g/kg (1g/10L)
What can I do to stop it coming back?
Can resprout from rhizomes and seed bank reinfests bared sites. Can be left in regenerating bush and shrubland, as will disappear as light levels fall. Chrysolina beetle has successfully reduced weed abundance since 1950s, and may need to be reintroduced in some areas - check with your regional council.