Thunbergia (Retz.) is a genus of roughly 150–153 accepted species of flowering vines and shrubs in the family Acanthaceae, subfamily Thunbergioideae, order Lamiales. Plants in this genus are characteristically vigorous growers, reaching 2–8 m tall, and exhibit a wide range of growth forms from twining climbers to upright shrubs. The genus is informally called "clockvines" after the characteristic spiralling habit of its climbing members.
The genus is native to the tropical and subtropical regions of sub-Saharan Africa, Madagascar, southern Asia (including India, Nepal, Sri Lanka, the Himalayas, and Southeast Asia), New Guinea, and northern Australia. Its core diversity is centred in Africa, with a secondary centre in Asia. Several species have been widely introduced beyond their native ranges through horticulture and have become naturalised or invasive in many tropical and subtropical regions globally, including the Americas, Pacific islands, and parts of the Old World.
Among the best-known members are Thunbergia alata, the black-eyed Susan vine, grown widely as a garden annual for its cheerful orange or yellow flowers with a dark eye, and Thunbergia grandiflora, the sky vine or Bengal clockvine, a vigorous perennial climber with large blue-violet flowers that is esteemed in tropical horticulture but listed as a weed in Australia. Thunbergia gregorii, the orange clockvine, is similarly popular in warm-climate gardens.
The genus name honours the Swedish botanist and physician Carl Peter Thunberg (1743–1828), a student of Linnaeus who collected extensively in Japan, South Africa, and elsewhere and is known as the "father of South African botany." The genus was established by the Swedish botanist Anders Jahan Retzius, who published the name in 1776.
Etymology
The generic name Thunbergia was given in honour of Carl Peter Thunberg (1743–1828), a Swedish naturalist, botanist, and physician who studied under Linnaeus. Thunberg conducted major collecting expeditions in Japan and southern Africa and is widely credited as the "father of South African botany." The genus was formally described and named by the Swedish botanist Anders Jahan Retzius, with the name published in 1776. The common name "clockvine," applied broadly across the genus, alludes to the spiralling, clock-like twining habit of the climbing species.
Distribution
The core native range of Thunbergia spans tropical and subtropical sub-Saharan Africa — from West African countries including Senegal, Guinea, Ghana, Nigeria, and Ivory Coast, through Central Africa (Cameroon, DRC, Congo, Gabon, Central African Republic), to East Africa (Kenya, Tanzania, Uganda, Ethiopia, Rwanda, Somalia) and southern Africa (South Africa's Cape Provinces, KwaZulu-Natal, Free State, Northern Provinces, Namibia, Mozambique, Zambia, Zimbabwe, Botswana, Eswatini). The genus is also native to Madagascar, and extends through southern and Southeast Asia, including India, Sri Lanka, the Andaman and Nicobar Islands, Nepal, the Himalayas (West and East), Bangladesh, Assam, Myanmar, Thailand, Laos, Vietnam, Cambodia, China (South-Central and Southeast), Hainan, Tibet, the Malay Peninsula, Borneo, Sumatra, Java, Sulawesi, Maluku, the Lesser Sunda Islands, the Philippines, and New Guinea. In Australasia, it is native to the Northern Territory and Queensland and also occurs in Western Australia.
Beyond its native range, Thunbergia has been widely introduced through horticulture and has become naturalised in many tropical and subtropical regions: across the Americas (Florida, Texas, Alabama, the Caribbean, Mexico, Central America, and South America), the Pacific Islands (Hawaii, Fiji, Samoa, Tonga, French Polynesia, New Caledonia, Vanuatu, and others), and Indian Ocean islands (Mauritius, Reunion, Seychelles, Rodrigues, Comoros). Distribution data is sourced from the World Checklist of Vascular Plants (WCVP) via GBIF.
Ecology
Several Thunbergia species have demonstrated significant invasive potential when introduced outside their native ranges. T. grandiflora, T. fragrans, and T. laurifolia are specifically noted as weeds in Australia, where they form dense mats capable of smothering native vegetation. T. grandiflora in particular is considered a serious environmental weed in Queensland and elsewhere in tropical Australia, and has also become naturalised in parts of the Americas and Pacific Islands. The climbing habit of many species allows them to overtop and shade out native plants, contributing to habitat degradation in susceptible ecosystems. The genus's broad establishment in introduced regions — spanning over 60 territories and island groups according to WCVP data — reflects the general adaptability of these plants to disturbed tropical and subtropical environments.
Cultivation
Thunbergia alata (black-eyed Susan vine) and T. gregorii (orange clockvine) are among the most widely cultivated members of the genus, grown as annuals or short-lived perennials in temperate gardens and as perennial climbers in frost-free climates. T. grandiflora (sky vine) is a popular large-flowered tropical climber prized for its cascades of blue-violet blooms. T. mysorensis, the mysore trumpetvine, is grown in warm climates for its pendulous clusters of yellow and maroon tubular flowers. The genus as a whole is valued in horticulture for its often showy, trumpet-shaped flowers in shades of orange, yellow, white, blue, and violet, frequently with a contrasting dark eye.
Taxonomy
Thunbergia is the type genus of the subfamily Thunbergioideae within the family Acanthaceae (order Lamiales). The genus was described by Anders Jahan Retzius in 1776 and is classified in the kingdom Plantae, phylum Tracheophyta, class Magnoliopsida. GBIF records 198 descendant taxa with 153 accepted species under the genus. The World Checklist of Vascular Plants (WCVP) is the authoritative checklist source for distribution data. No nomenclatural issues are recorded in GBIF as of the 2023-08-22 interpretation.
