Red silk-cotton tree

The red silk-cotton tree is a deciduous tree averaging about 20 m and reaching up to 60 m in humid tropical regions; the trunk is straight, the base buttressed, and the stems and young branches bear many sharp conical spines that wear down with age. The leaves are palmate with 5–7 leaflets (usually 6) radiating from the tip of the petiole; the blade is 13–15 cm long, 7–10 cm wide and the petiole up to 20 cm. The flowers are bisexual, large, red to orange, cup-shaped and 7–11 cm across, borne singly or in clusters in the axils near the ends of the branches while the tree is leafless; the petals reach 12 cm, the calyx is cup-shaped with three lobes, the stamens number more than 60 in five bundles and the stigma is red. The fruit is a capsule about 13 cm long holding many black or grey seeds embedded in fine white floss (the silk cotton) and splits open when ripe. The bark is grey, smooth on old trees, and marked with old spine scars.

According to Kew POWO the species is native to tropical South and Southeast Asia and northern Australia: Pakistan, India, Nepal, Bhutan, Bangladesh, Sri Lanka, Myanmar, southern China (Yunnan, Guangdong, Guangxi, Hainan and more), Taiwan, Laos, Thailand, Cambodia, Vietnam, Malaysia, Indonesia (Java, Sumatra, Sulawesi, Maluku, Lesser Sunda Islands), the Philippines, New Guinea, the Bismarck Archipelago, the Solomon Islands and Australia's Northern Territory. It grows in tropical rainforest and dry deciduous forest, along rivers and roads on low ground, and has been widely planted throughout the tropics of Africa, the Caribbean and the Americas as a shade and ornamental tree. Chinese records relate that Zhao Tuo, king of Nam Viet, gave a silk-cotton tree to the Han emperor in the 2nd century BC. It flowers from about February to May while leafless, and is the city flower of Guangzhou and a symbol of Cantonese culture.

The tree's signature constituent is the silk cotton in the fruit — chiefly cellulose, fine, light, weakly elastic and water-repellent, so it cannot be spun into strong yarn like cotton. The flowers are rich in phenolic compounds: flavonols (quercetin, kaempferol, shamimin), flavones (vicenin-2, linarin, saponarin, isovitexin, apigenin, xanthomicrol), xanthones (mangiferin, shamimoside), together with naringenin, ferulic acid, syringin and anthocyanins (glucosides of pelargonidin and cyanidin) that give the red-orange colour. Triterpenoids and steroids include β-amyrin with its acetate and palmitate derivatives, β-amyrone, lupeol, β-sitosterol and the coumarin isoscopoletin (isolated from the leaves). The bark contains a polysaccharide gum with tannins, catechutannic acid, lupeol and β-sitosterol; the seeds contain fatty oil, hexacosanol and tocopherol, while the roots and root bark hold naphthoquinones such as bombamalabin and isohemigossypol-1-dimethyl ether.

The silk cotton is used to stuff pillows, mattresses and life jackets and as sound and heat insulation; in Nepal and India the fibres are carded and woven into cloth. Young calyces and flowers are eaten as a vegetable, and the dried flower cores flavour Thailand's nam ngiao and kaeng khae. The soft, light wood serves for boxes, matches, toys and pulp, and the tree is planted for shade, as an ornamental and in agroforestry. In traditional medicine the bark, roots and flowers treat diarrhoea, dysentery, fever, wounds and other ailments, hence the name “silent doctor”. In research, Faizi & Ali (1999) isolated shamimin from the leaves; Saleem et al. (1999) showed shamimin lowers blood pressure and blood glucose; El-Hagrassi et al. (2011) isolated seven flavones from the flowers; Faizi et al. (2012) found the antioxidant xanthone shamimoside; Zhang et al. (2015) identified 23 phenolic compounds from the flowers with antioxidant and antiviral activity; Meena & Chaudhary (2017) reviewed the pharmacology; and Taher et al. (2024) demonstrated antioxidant, hypoglycaemic, analgesic and antidiarrhoeal effects of the leaf extract in mice.

The tree is relatively safe; the conical trunk spines can injure anyone who brushes against them, and breathing large amounts of the cotton floss may irritate the airways. Medicinal preparations from the bark, roots and flowers lower blood glucose and blood pressure, so they warrant caution alongside diabetes or blood-pressure medication, and some traditional uses lack full clinical validation. On conservation, the IUCN lists Bombax ceiba as Least Concern (LC) in its 2020 assessment (Barstow, e.T61781914A61781917) owing to its wide range and widespread planting. Though not globally threatened, local populations face logging, land conversion and urbanisation; protecting old silk-cotton trees and local stands retains cultural and ecological value.