Cleistocalyx

Vối is an evergreen tree 10–20 m tall with smooth grey bark and a dense crown. Its opposite, lanceolate leaves are 8–15 cm long on short stalks, leathery with a paler underside. The cymose inflorescences arise in the leaf axils; the flower buds bear a cap (operculum) that covers the bud and pops off at anthesis — a hallmark of the genus. The fruit is a globose berry ripening dark purple-black and containing 1–2 seeds.

According to Kew POWO, vối is native to tropical and subtropical Asia extending to northern Australia: India (Assam, East Himalaya), Nepal, Bangladesh and Sri Lanka; southern China (Guangdong, Guangxi, Yunnan, Hainan, Tibet) and Taiwan; Cambodia, Myanmar, Thailand and Vietnam; Borneo, Java, Malaya, Maluku, the Philippines, Sumatra, the Lesser Sunda Islands and Christmas Island; and northern and western Australia. In Vietnam it grows in moist places along rivers, ponds and alluvial soil and is often planted at temples and village roadsides.

Between 2002 and 2019, phytochemical studies identified 86 compounds from vối leaves and flower buds, falling into three main classes: oleanane/ursane triterpenoids, C-methylated flavonoids (chiefly chalcones) and polycyclic phloroglucinols (Pham et al., 2020). The most studied active is the C-methylated chalcone DMC (2′,4′-dihydroxy-6′-methoxy-3′,5′-dimethylchalcone), present in leaves, buds and seeds. DMC content in the buds is about 0.97–1.20 mg/g and ursolic acid 2.86–3.55 mg/g of dried material. The leaves and buds also contain kaempferol, quercetin, myricetin, tamarixetin, monoterpene-bearing phloroglucinols (cleistoperlone A) and an essential oil with β-caryophyllene, α-terpineol and caryophyllene oxide.

A decoction of young leaves and dried buds is a traditional drink in Vietnam and southern China, used for colds, fever, sore throat and digestive upset; the leaves and buds are also applied externally for bruises, acne and skin ulcers (Pham et al., 2020). Modern studies show DMC is selectively cytotoxic to several cancer lines (IC50 32.3 µM against SMMC-7721) and reverses multidrug resistance; C-methylated flavonoids inhibit influenza H1N1 neuraminidase (IC50 8.15–93.77 µM), more potently against the oseltamivir-resistant H274Y strain; and cleistoperlone A inhibits HSV-1 (IC50 7.50 µM). Bud extract and DMC protect mice from endotoxic shock via the Nrf2/HO-1 pathway (2019), while chalcone–monoterpene derivatives inhibit PTP1B (IC50 0.9–3.9 µM), suggesting antidiabetic potential. The ripe fruit is edible and used for jam and juice in Thailand; the wood is used for joinery.

Vối tea is regarded as safe at usual drinking strength; however, pharmacological evidence remains largely in vitro and animal-based, with no human clinical trials, so prolonged concentrated use or self-medication with isolated DMC is not advised. The IUCN assesses vối as Least Concern (LC) and the species is not listed by CITES; it is widespread with a large population and widely planted, though old riverside trees should be retained as a seed source.