Alstonia Genus

Alstonia is a widespread genus of evergreen trees and shrubs in the dogbane family, Apocynaceae (order Gentianales). The genus was named by the botanist Robert Brown in 1811 and, depending on the authority, comprises roughly 40 to 60 species; Plants of the World Online accepted about 44 species as of April 2025. Its type species is Alstonia scholaris, which Linnaeus had originally described as Echites scholaris in 1767.

Members of the genus are native to the tropical and subtropical regions of Africa, Central America, Southeast Asia, Polynesia and Australia, with the greatest concentration of species in the Malesian region. Many are substantial trees—A. pneumatophora has been recorded at 60 metres tall and more than 2 metres in diameter—while A. longifolia, the only species reaching Central America, ranges from shrubs to trees about 20 metres high.

The leaves of Alstonia are leathery, sessile and simple, borne in opposite pairs or in whorls. The inflorescence is terminal or axillary and bears small, more or less fragrant, funnel-shaped flowers that may be white, yellow, pink or green; each has five petals and five sepals. The fruit is a distinctive deep-blue, pod-like schizocarp between 7 and 40 centimetres long. As in many Apocynaceae, the plants exude a milky latex that is rich in poisonous alkaloids. The genus is divided into five monophyletic sections—Alstonia, Blaberopus, Tonduzia, Monuraspermum and Dissuraspermum.

Alstonia trees are widely used in traditional medicine, and many species are harvested for timber, known as pule or pulai in Indonesia and Malaysia. The latex also has local uses; in Fiji, the latex of A. costata is used as a kind of chewing gum. While most Alstonia are common and not threatened, a handful of species—such as A. annamensis, A. beatricis and A. guangxiensis—are very rare.