Bombax is a genus of mainly tropical trees belonging to the mallow family Malvaceae, order Malvales. The genus is native to western Africa, the Indian subcontinent, Southeast Asia, subtropical East Asia, and northern Australia, and its most celebrated member, Bombax ceiba, is now widely cultivated across tropical and subtropical regions worldwide.
Plants in this genus rank among the largest trees in their native landscapes, commonly reaching 30 to 40 metres in height with trunks that can measure up to three metres in diameter. The leaves are palmate and deciduous, shed during the dry season; they span 30 to 50 centimetres across and carry five to nine leaflets. One of the genus's most striking features is its flowering season: showy red flowers five to ten centimetres long appear between January and March while the tree is entirely bare of leaves, making the blooms conspicuous against the bare crown. The calyx is deciduous and does not persist on the fruit. Stamens are arranged in two whorls in bundles, and the staminal column lacks lobes.
When the ovary matures, it produces a husk containing seeds wrapped in a cellulose fibre similar to kapok (Ceiba pentandra). The fibre is buoyant, water-resistant, and a poor thermal conductor, making it commercially valuable for filling sleeping bags, life preservers, pillows, and mattresses — though its short staple length prevents it from being spun as a textile. Bombax is distinguished from the closely related genus Ceiba primarily by its red (rather than white) flowers.
Eight species are currently recognised by Plants of the World Online, with several former members — including Pachira aquatica, Ceiba pentandra, and Ochroma pyramidale — reassigned to other genera over time. Bombax species also serve as larval food plants for certain Lepidoptera, including the leaf-miner Bucculatrix crateracma, which feeds exclusively on Bombax ceiba. Common names for the genus include silk cotton tree, red cotton tree, simal, and kapok.
Etymology
The genus name Bombax derives from the Greek bombyx (βόμβυξ), meaning silk or silkworm, a reference to the silky kapok-like fibres surrounding the seeds. Common vernacular names — silk cotton tree, red cotton tree, simal, and kapok — similarly reflect the cotton-resembling seed fibre that distinguishes the genus.
Distribution
Bombax is native to western Africa, the Indian subcontinent, Southeast Asia, subtropical East Asia, and northern Australia. Bombax ceiba, the most widely known species, is also extensively cultivated throughout tropical and subtropical regions globally.
Taxonomy Notes
Bombax has a complex nomenclatural history: numerous species formerly placed in the genus have been transferred to related genera including Ceiba, Pachira, Pseudobombax, Cochlospermum, and Ochroma. Plants of the World Online currently recognises eight species (as of March 2026). GBIF places the genus in Malvaceae (order Malvales), consistent with the APG IV circumscription of a broadly defined mallow family that absorbs the former Bombacaceae.
Cultural Uses
The seed fibres of Bombax species, known commercially as kapok, are 100% cellulose, buoyant, water-resistant, and thermally insulating. They are used as stuffing for pillows and mattresses and as insulation in sleeping bags and life preservers. The genus has cultural prominence in parts of Africa: the West African species Bombax buonopozense (the red-flowered silk cotton tree) holds significance in local traditions, and a tree of this type appears on the flag of Equatorial Guinea.
