Combretum is a large genus of flowering plants in the family Combretaceae, comprising roughly 270 to 290 accepted species depending on the authority consulted. Plants in the genus span a striking range of growth forms, from substantial canopy trees and shrubs of African savannahs to scandent climbers and lianas that thread through tropical forest understories. The genus was described by the Swedish botanist Pehr Löfling in 1758 and serves as the type genus of family Combretaceae within the order Myrtales.
The most distinctive feature of Combretum is its fruit. Species produce characteristic four- or five-winged samaras — papery, dry fruits whose flattened wings catch the wind and disperse seeds across the open savannahs and woodlands where many species grow. Although the broad foliage and weeping habit of some Combretum trees can be reminiscent of willows, the two groups are not closely related; the resemblance is purely superficial. Flowers in the genus are often small and clustered into spikes, racemes, or dense heads, and in several ornamental species the inflorescences are vividly red, orange, or pink, attracting birds, insects, and in rare cases non-bat mammals as pollinators.
Combretum has a pantropical native range. The greatest diversity is concentrated in tropical and southern Africa, with additional centres of species richness in tropical Asia (India, Bangladesh, China, Myanmar, Thailand, and the Philippines) and the Americas (Brazil, Colombia, Peru, Venezuela, Central America, and the Caribbean). A handful of species occur in Madagascar, New Guinea, the Bismarck Archipelago, and Australia. Across this range, bushwillow trees and shrubs are often ecologically dominant components of savannah, bushveld, and gallery-forest communities, particularly on granitic soils in southern Africa.
The genus is economically and culturally important in much of its range. Several species are pillars of traditional African and Indian herbal medicine, used to treat ailments from stomach complaints and diarrhoea to respiratory problems. Combretum imberbe, the leadwood tree, produces some of the densest, most durable timber in southern Africa and is used for fence posts, railway sleepers, and furniture. Pharmacologically, Combretum afrum is the source of the combretastatins, a family of compounds that have been investigated in clinical trials as anti-cancer agents. Ornamentally, the genus is best known for spectacular flowering climbers such as Combretum indicum (the Rangoon creeper, formerly Quisqualis indica), Combretum grandiflorum, and Combretum racemosum, which are widely grown in tropical gardens for their dense, brightly coloured flower clusters.
Etymology
The genus name Combretum was published by the Swedish botanist Pehr Löfling in 1758 in his Iter Hispanicum (page 308). It is the type genus of the family Combretaceae and is a conserved name (nom. cons.) under the International Code of Nomenclature for algae, fungi, and plants.
Distribution
Combretum has a pantropical native distribution. Its centre of diversity lies in tropical and southern Africa, where bushwillows are among the most conspicuous components of savannah and woodland vegetation, and about five species reach Madagascar. Beyond Africa, the genus extends across tropical Asia — including India, Bangladesh, China, Myanmar, Thailand, and the Philippines — and into New Guinea, the Bismarck Archipelago, and parts of Australia. A separate set of species occupies the American tropics, from Brazil, Colombia, Peru, and Venezuela through Central America and the Caribbean. Across this range, members of the genus occupy habitats ranging from dry savannah and bushveld (often on granitic soils) to gallery forest and seasonally flooded riverbanks.
Ecology
Bushwillows are frequently keystone or dominant trees in their habitats, particularly in African savannahs developed on granitic substrates, where they help structure plant communities and provide forage and habitat for wildlife. Pollination biology in the genus is unusually varied: most species are pollinated by insects or birds, but a small number are pollinated by non-flying mammals, an ecological strategy that is rare among flowering plants generally. The genus's characteristic 4- to 5-winged samara fruits are wind-dispersed, an adaptation well suited to the open habitats where many species occur.
Cultivation
Combretum is grown primarily in frost-free tropical and subtropical climates. Cultivated members of the genus include the spectacular flowering climbers Combretum indicum (Rangoon creeper, transferred from the formerly separate genus Quisqualis), Combretum grandiflorum, and Combretum racemosum, all valued for showy clusters of red, orange, or pink flowers. Where species have been documented horticulturally — for example the leadwood tree Combretum imberbe — they are hardy only in USDA zones 10–12, require full sun and well-drained soil, and grow extremely slowly, with trunk diameters increasing by only 0.3 to 2 millimetres a year. Established plants tolerate drought reasonably well once their root systems are mature.
Propagation
Where propagation has been documented, as in Combretum imberbe, seeds are pre-soaked in warm water for a few hours and then pressed into seedling trays of river sand. Germination occurs within one to two weeks, but viability is low and germination rates of only 3 to 5 percent are typical, so growers usually sow large quantities to obtain useful numbers of seedlings.
Cultural & Economic Uses
Combretum is deeply woven into traditional pharmacopoeias across its range. Several species feature in African and Indian herbal medicine, where root, bark, and leaf preparations are used to treat stomach pain, diarrhoea, coughs, and chest complaints, and the smoke of burning leaves is inhaled for respiratory ailments. The leadwood tree, Combretum imberbe, also supplies leaves eaten as a green vegetable and an edible gum of medium quality used in confectionery; its wood ash has historically served as a toothpaste substitute, and its bark yields tannins. In modern pharmacology, Combretum afrum is the source of the combretastatins, a family of compounds that have been investigated in clinical trials as anti-cancer agents, including for anaplastic thyroid cancer. Bushwillow timber, especially that of Combretum imberbe, is extremely dense and durable and is used for fence poles, railway sleepers, and furniture.
Taxonomy
Combretum was described by Pehr Löfling in 1758 (Iter Hispanicum, p. 308) and is a conserved name. It sits in family Combretaceae, order Myrtales, in the kingdom Plantae, and is the type genus of its family. Estimates of species number vary by source: Plants of the World Online recognises approximately 290 accepted species, the Wikipedia treatment cites around 272, and GBIF records 424 descendant names under the genus (a figure that includes synonyms and infraspecific taxa). POWO lists 27 heterotypic synonyms, including the formerly accepted genera Quisqualis L., Grislea L. (rejected name), Poivrea Comm. ex DC., and Thiloa Eichler, several of which have been merged into Combretum on the basis of molecular evidence.
