Quick Facts

Quick facts

• Blue Trumpet Vine (Thunbergia grandiflora) is a native plant of India that was most likely introduced to Australia in the 1950s or 60s.
• Blue Trumpet is a very vigorous climbing vine which is capable of smothering vegetation in tropical rainforest areas.
• It is a major threat to remnant vegetation in the Wet Tropics.
• Early intervention is crucial otherwise the tuberous system of roots makes it difficult to remove – only one herbicide has proved effective.
• Prevent the discarding of garden waste or soil containing parts of the plant in order to prevent establishment of new populations.

What Does It Look Like?

What is it?

Blue Trumpet Vine (Thunbergia grandiflora) is a vigorous, scrambling vine with tuberous roots. Leaves are oppositely arranged, have petioles (the leaf stalk) 1–6 cm long, with the main part of the leaf being 3–12 cm long and 3.5–14 cm wide and usually has 4–5 lobes.

Towards the end of the branches there are 2–4 flowers at each of the nodes. These flowers are on a stalk up to 3 cm long and the base of the flower is covered by a pair of 3 cm long leafy bracts which are fused together along one entire side and part of the other. These bracts are covered all over with velvety hairs but also have some small cup-shaped glands (looking like black dots) which secrete nectar and attract ants. The calyx is hidden by the bracts and is an entire ring with nectaries (nectar-producing glands physically apart from the flower) all over it, but these are usually obscured by stiff erect hairs; this ring remains in fruit.

The flower, which can be up to 8 cm diameter, has a 3-4 cm long tube and 5 lobes, each 2 cm long and usually pale to mid-blue, with the inside of the throat a paler colour except for some darker lines on the lower lip.

The fruit capsules have a globose basal portion about 1.5 cm wide which is topped by a beak up to 2 cm long; the globose portion holds up to 4 hollowed out seeds each about 8 mm diameter (Barker 1986).

For further information and assistance with identification of Blue Trumpet Vine contact the herbarium in your state or territory.

Flower colour

Blue

Growth form (weed type/habit)

Vine

Where it currently grows? Preferred habitat

Blue Trumpet Vine is found along watercourses, on forest margins, in open woodlands, along roadsides and fence-lines and in gardens and plantation crops in tropical and sometimes also subtropical regions (Navie 2004).

Are there similar species?

Laurel Clock Vine (Thunbergia laurifolia) and Blue Trumpet Vine (Thunbergia grandiflora) are so similar that there is some doubt that they are different species. The most useful distinction between them in Australia is the unlobed leaves of T. laurifolia and the lobed leaves of T. grandiflora (Barker 2007, pers. comm.).

Neither species is likely to be confused with the other Thunbergia species in Australia. T. arnhemica and T. fragrans both have white-flowers and T. alata has an orange flower with a black throat. None of these have the ability to climb in the same way as T. laurifolia and T. grandiflora although they can form smothering populations at ground level (Barker 2007, pers. comm.).

Why Is It A Weed?

What are its impacts?

Blue Trumpet Vine was included in the list of 71 species that were nominated by state and territory governments for assessment as Weeds of National Significance (WONS). Following an assessment process, Blue Trumpet Vine was not included as one of the 20 WONS. However, it remains a weed of potential national significance.

Native ecosystems: Blue Trumpet Vine is a major threat to monsoon vine thickets and remnant tropical rainforests across northern Australia. Its ability to climb to the top of tall trees as well as across the top of lower vegetation eventually leads to smothering of the supporting species, often native, and may lead to the fall of mature trees because of the weight of the vine (Navie 2004, Qld DAF 2020).

In 1982 when enquiries were made as to the status of the plant in the Cairns region there was apparently very little knowledge of it, but by 1985 it was recognized as a problem in Johnstone Shire (Barker 1986).

How does it spread?

Dispersal of Blue Trumpet Vine is by seeds, cuttings, and fragments of stems and roots. The root tubers formed can be enormous, as large as a small car (CRC 2003). Dumping of garden cuttings is the most likely means of spread since new plants can be produced from the nodes and from the tuberous roots. Seed production is by far the least effective means of dispersal of the plant.

What is its history in Australia?

It is not known when Blue Trumpet Vine first arrived in Australia. It seems likely that it may have been introduced in the Cairns region in the 1950s or 1960s, possibly from Papua New Guinea, but it is also quite possible that introduction to the southern states may have been earlier but not spread to the same extent (Barker 2007, pers. comm.).

How To Manage It?

Best practice management

Chemical control: Spraying or injecting with herbicides is often the only option and this has provided effective control in the past. Whichever herbicide is recommended it is unlikely that one application will achieve complete eradication. Monitoring and follow-up will be needed (Land Protection 2007). Contact the weed management agency in your state or territory for advice.

Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au.

Non-chemical control: Physical control: The cutting of Blue Trumpet Vines at ground level is usually not effective since plants will regenerate from their underground tubers. Small plants may be dug out, but established plants normally have too extensive a system of tubers.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Blue Trumpet Vine grows rapidly in tropical and subtropical climates. Peak flowering is from September to December but flowers may still be observed outside these months. From observations of herbarium specimens, fruits are formed, but not prolifically, suggesting that effective pollinators may not be present in Australia or that the flowers are not self-compatible (Barker 2007, pers. comm.).

Little is known about seed formation, seed drop and germination in this species. It was originally thought that Thunbergia species in Australia might not produce viable seed, but successful germination of seeds has now been recorded for the very similar Laurel Clock Vine (T. laurifolia) (CRC 2003).

Where Is It Found?

Which states and territories is it found?

NT, QLD

What areas within states and territories is it found?

Sporadic populations of Blue Trumpet Vine are found along the entire eastern Queensland coastline with particularly dense infestations recorded in the Cairns area. Neither this species nor laurel clock vine (T. laurifolia) has been recorded as naturalised for the Northern Territory in their checklist of introduced plants (Cowie & Kerrigan 2007) although herbarium records exist for Darwin and Jabiru (AVH). It is cultivated occasionally in gardens in southern states as well (Barker 2007, pers. comm.).

Where does it originate?

Blue Trumpet Vine is an Indian species which has been spread around the tropics because of its very ornamental flowers and its ability to quickly cover unsightly areas (Barker 1986).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

QLD, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Thunbergia grandiflora

Other scientific names (synonyms)?

Does it have other known common name(s)?

Blue Thunbergia, Bengal Clock Vine, Sky Flower, Blue Sky Flower, Thunbergia