blue thunbergia

Thunbergia grandiflora
Vine
Opposite
Simple
White
Purple
Green

A long-lived vine, with tuberous roots, that grows up to 15 m in height. Its younger stems are square in cross-section and bear oppositely arranged leaves on stalks 4-12 cm long. These leaves are variable in shape and their margins usually have several large teeth or small pointed lobes. Its pale blue, violet or mauve trumpet-shaped flowers (3-8 cm long and 6-8 cm across) have a pale yellow or whitish coloured throat. Each flower is borne on a long stalk (4-5 cm long) and has two leafy bracts (15-40 mm long) at its base. Its fruiting capsules, when produced, are rounded with a long tapered beak (2-5 cm long).

Common names 
Also known as: Bengal clock vine, Bengal trumpet, blue sky flower, giant thunbergia, blue sky vine, clock vine, blue thunbergia , blue trumpetvine,
Family 
Acanthaceae
Deciduous 
No
Flowering time 
Spring-Summer
Native/Exotic 
Exotic
Origin 
This species is native to the Indian sub-continent (i.e north-eastern India, Bhutan and Nepal), southern China and Myanmar.
Notifiable 
No
State declaration 
Category 3 - Must not be distributed or disposed. This means it must not be released into the environment unless the distribution or disposal is authorised in a regulation or under a permit.
Council declaration 
As per State Declaration
Known distribution 

Blue thunbergia (Thunbergia grandiflora ) is reasonably widespread in the coastal districts of northern Queensland and is most common in the Cook pastoral district. Scattered populations are also present in the coastal districts of central and south-eastern Queensland. Also naturalised in tropical South America, Central America (i.e. Costa Rica), south-eastern USA (i.e. Florida), the Mascarenes (i.e. the Seychelles and La Réunion) and on some Pacific islands (i.e. Fiji, Western Samoa, Palau and Hawaii).

Habitat 

A weed of watercourses (i.e. riparian areas), disturbed closed forests, forest margins, open woodlands, roadsides, fence-lines, gardens and plantation crops in tropical and sub-tropical regions.

Habit 

A long-lived (i.e. perennial), vigorous, climbing plant that can smother trees and grow up to 15 m in height.

Impact and control methods 

Blue thunbergia (Thunbergia grandiflora) is regarded as a significant environmental weed in Queensland, and as a potential environmental weed or "sleeper weed" in the Northern Territory and New South Wales.

Stem and leaves 

green, hairy (i.e. pubescent), and square in cross-section (i.e. quadrangular). The older climbing stems are quite thick when mature, and they usually turn brown in colour and become somewhat rounded in shape. The oppositely arranged leaves are borne on hairy stalks (i.e. pubescent petioles) 4-12 cm long. These leaves are variable in shape (8-22 cm long and 3-15 cm wide) and may have broad heart-shaped (i.e. cordate) bases, be somewhat triangular in shape, or be roughly egg-shaped in outline (i.e. ovate). Their margins are also quite variable, and can range from being almost entire, to being irregularly toothed (i.e. crenated) or have several irregular, pointed lobes. The leaves are also bright green in colour and somewhat hairy (i.e. pubescent).

Flowers and fruits 

The trumpet-shaped (i.e. tubular) flowers are borne in elongated clusters (i.e. racemes) on long, drooping (i.e. pendent) branches. They are large and showy (3-8 cm long and 6-8 cm across) with five pale blue, violet or mauve coloured petal lobes and a pale yellow or whitish coloured throat. Each flower is borne on a stalk (i.e. pedicel) 4-5 cm long and has two leafy bracts (i.e. bracteoles) at its base. These bracts (15-40 mm long and 10-20 mm wide) are oblong or egg-shaped in outline (i.e. ovate) and have pointed tips (i.e. acuminate apices). The flowers also have hairy (i.e. pubescent) sepals that are fused together and reduced to a ring-like structure (i.e. calyx tube) that is greenish-coloured and may sometimes be streaked with purple or red. Flowering occurs throughout the year, but is most abundant during summer and autumn. [Note: there is also a relatively common white-flowered horticultural variety known as Thunbergia grandiflora 'Alba']. The fruit is a capsule with a rounded (i.e. spherical) base (about 18 mm long and 13 mm across) and a long tapered beak (2-5 cm long and about 7 mm wide). These fruit are only produced in the warmer parts of northern Australia. The large, flattened (i.e. compressed), seeds (up to 10 mm across) are smooth on one side and warty on the other side.

Reproduction and dispersal 

This species reproduces via seed (but fruit are only produced in warmer climates) and is also capable of regenerating from stem fragments or portions of the tuberous roots.It has been widely cultivated as an ornamental and is most commonly dispersed in dumped garden waste. The tuberous roots may also be spread during soil moving activities (e.g. roadworks) and by flood waters. Seeds are explosively released, and may be catapulted several meters when the ripe fruiting capsules split open at maturity.

Similar species 

Blue thunbergia (Thunbergia grandiflora) is very similar to laurel clock vine (Thunbergia laurifolia) and relatively similar to fragrant thunbergia (Thunbergia fragrans), black-eyed Susan (Thunbergia alata) and the native species Thunbergia arnhemica.Although laurel clock vine (Thunbergia laurifolia) is so similar to blue thunbergia (Thunbergia grandiflora) that the characters of these species almost overlap, it can usually be distinguished by the following differences: blue thunbergia (Thunbergia grandiflora) usually has relatively broad leaves bearing relatively large pointed lobes and/or toothed margins. It leaves are usually hairy (i.e. pubescent) and are borne on relatively long hairy stalks (4-12 cm long).laurel clock vine (Thunbergia laurifolia) usually has relatively narrow leaves that are almost entire or have shallowly lobed or toothed margins. Its leaves are hairless (i.e. glabrous) and are borne on relatively short stalks (usually less than 3 cm long). Blue thunbergia (Thunbergia grandiflora) can be more easily distinguished from the other species by the following differences: blue thunbergia (Thunbergia grandiflora) has large flowers (60-80 mm across) that are usually blue or purplish in colour (white in Thunbergia grandiflora 'Alba') with broad throats that are pale yellowish in colour.black-eyed Susan (Thunbergia alata) has relatively small flowers (25-40 mm across) that are usually orange (white in Thunbergia alata 'Alba') with conspicuous blackish coloured throats that are quite narrow.fragrant thunbergia (Thunbergia fragrans) has moderately large flowers (about 50 mm across) that are entirely white in colour and have a very narrow throat.Thunbergia arnhemica has moderately large flowers (about 50 mm across) that are entirely white in colour and are bell-shaped with a relatively broad throat.