| Text and Pictures by Lalith Gunasekera
( July 25, 2014, Mackay - Queensland, Sri Lanka Guardian) Thunbergia is a vigorous, perennial climbing vine, commonly grown in many garden in South East Asia and Australia mainly in tropical climatic conditions. This species is native to India and Malaysia. Thunbergia species were introduced to many countries as garden ornamentals but escaped into native vegetation. It was introduced to Australia as garden ornamentals but escaped into native vegetation. This species was popular with gardeners due to their large flowers and climbing habit. Thunbergia (following three species) is a declared plant under Queensland- Australia legislation.
1. Blue Thunbergia – There are two species of blue Thunbergia (THUNBERGIA GRANDIFLORA AND THUNBERGIA LAURIFOLIA) with blue flowers have been seen in Sri Lanka, Australia, South East Asia and China andcommonly known as Bengal clock vine, Bengal trumpet or blue sky vine. These species have leaves of the same size but with different shapes. T. grandiflora has leaves which are broad at the base, lobed, narrowing to a pointed tip whileT. laurifolia has oval shaped leaves with edges that are not lobed as such.
2. White Thunbergia – This species is THUNBERGIA FRAGRANS has white flower and known as white lady, sweet clock vine, and fragrant thunbergia.
Thunbergia takes its name from a Swedish scientist Professor. Carl Peter Thunberg who had visited Japan and then Sri Lanka during the time the country was under the Dutch rule and collected some plants for his studies.
Blue Thunbergia species are vigorous, perennial climbing vines. Both species have oval shaped leaves which narrow to a pointed tip. Leaves form on opposite sides of the stem and are up to 15 cm long and 10 cm wide. The main reason for its popularity is its attractive flower which takes the shape of a trumpet with a short, broad tube. It is white on the outside with a yellowish throat and opens out into five rounded pale lavender blue petals, one larger than others up to 8 cm long and 6-8 cm wide.
Thunbergia flower produces seed pods which are cone shaped and 3-5 cm long capsules. It contains 2-4 flat seeds up to 1 cm long covered in brown scales and when the ripe pod splits, it is catapulted several meters.
Picture 1: Blue Thunbergia (Thunbergia laurifolia) flowers and leaves with smooth margins.
Picture 2: Blue Thunbergia (Thunbergia grandifolora) flowers and leaves with serrated margins.
The vine has extensive underground tubers with some being large as 70 kg. A smothered tree will get a new lease of life if the thunbergia vine is cut at ground level, but the vine will regenerate if the tubers are not destroyed.
Thunbergia mainly reproduces by vegetative materials 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 soil being removed for fill or other use. Infestations along waterways have been caused by root pieces breaking off and being transported downstream by flood waters.
This species also a popular with home gardens in Sri Lanka and some Asian countries and Northern Australia. The slender, green or reddish stems are square in cross section and somewhat hairy when young. These stems bear pairs of oppositely arranged leaves that have petioles (stalks) about 4 cm long. Leaves are 4-12 cm long and 3-5 cm wide and egg shaped in outline or somewhat triangular with arrow shaped bases. The leaf margins are varying from being slightly lobed to toothed or almost entire.
Picture 3: White Thunbergia (Thunbergia fragrans) flowers and leaves – egg shaped leaves.
The white, tubular flowers are 4-6 cm across are borne singly or in pairs on stalks emerging from leaf joints. Each flower is subtended by two leaf bracts. The flower tube is narrow -1.5 – 3 cm long and topped with five broad, white petals. Flowering occurs throughout the year, but mostly during summer and autumn in Australia. The fruit is an almost rounded capsule topped with a long thick beak up to 2 cm long.
White Thunbergia reproduces by seed and also vegetatively by fragments of stems and roots. Dispersal of this species is usually facilitated by it being grown in gardens with stem fragments and seeds subsequently being spread in dumped garden waste.
Thunbergia species are a major threat to tropical rainforests across the world. They climb and smother native vegetation, shading out and killing the understory and often pulling down mature trees with the weight of the wine.
Picture 4: Thunbergia invading the Kelani River Bank near Ruwanwella – Sri Lanka
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 plant will regenerate from tubers. The follow up control work will be required totally manage infestations.
( The writer is an Invasive Plants Specialist