Thunbergia species were introduced to Australia as garden ornamentals but have escaped into native vegetation, and four species are now declared weeds in Queensland. They climb and smother native vegetation, shading out and killing the understorey and often pulling down mature trees with the weight of the vine.
Laurel clock vine is native to India and Malaysia. Until recently Thunbergia species, including laurel clock vine, were promoted and sold as garden plants. They are widespread in Queensland gardens, and are also common in eastern Australia as far south as Melbourne and occasionally extending to Adelaide, as well as across northern Western Australia and the Northern Territory (Darwin), and on Christmas Island. There are naturalised infestations in far north Queensland and Northern Territory.
Laurel clock weed mainly reproduces vegetatively, when cuttings or fragments of stems and roots take root and send out new shoots. It is often spread through the careless disposal of garden waste, or through contaminated earth being removed for fill or other soil use. Infestations along riverbanks have been caused by root pieces breaking off and being transported further downstream by floodwaters.
Laurel clock vine is a vigorous, perennial climbing vine.
It has oval-shaped leaves which narrow to a pointed tip. The leaves, mostly 70–180 mm long and 25–60 mm wide, grow in opposite pairs along the stem on stalks up to 60 mm long.
The trumpet-shaped flower begins as a short broad tube, white on the outside with a yellowish throat, and opens out into five rounded, pale lavender-blue petals, one larger than the others. The flowers are up to 80 mm long and 60–80 mm across, and are borne in clusters on long, drooping branches.
The seed capsule is brown and inconspicuous. It is oval-shaped with pinched ends (ie elliptical), 10 mm long and 4 mm wide. The capsules usually contain two to four hemispherical seeds which have a hollow inner surface like a cap. The seeds are less than 10 mm in diameter and covered with brown scales.
The plant develops a very tuberous root system, which can resprout from many dormant buds when cut.
Laurel clock vine grows in moist areas at low elevations and is most successful in frost-free locations.
CRC for Australian Weed Management: Robyn Barker (SA Plant Biodiversity Centre), Peter van Haaren (Qld DNRM), Ken Murray (Cairns City Council), Sid Clayton (Mareeba Shire Council), Barbara Waterhouse (AQIS/Weeds CRC), Steve Csurhes (Qld DNRM), Philip Maher (Qld DNRM) and John Thorp (National Weeds Management Facilitator).
Control of Thunbergia species is very difficult because they can regenerate from extensive underground tubers if they are not all killed or removed. Consequently, any control of T. laurifolia should be undertaken cooperatively with your state or territory weed management agency or local council.
Chemical treatment is often the only option available. Check registered herbicides. Only small plants can be successfully controlled using physical removal because large mature plants normally have very large tuber systems that are virtually impossible to remove completely.
Cutting the vines at ground level will provide some temporary relief for a smothered tree but plants will regenerate from tubers, so follow-up control will be required.
Replace specimens of T. laurifolia and T. grandiflora in gardens, using local native species where possible.
Take care when disposing of Thunbergia species because garden waste is a frequent source of new weed infestations. Contact your local council for specific advice before attempting to dispose of this plant.
Laurel clock vine (Thunbergia laurifolia) is not declared in NSW under the Noxious Weeds Act 1993.