Alstonia is a genus of evergreen trees and shrubs in the dogbane family, Apocynaceae. There are Alstonia species native to tropical areas of Africa, Australia, Central America, Polynesia, and southeast Asia. The trees can reach 200 feet (60 meters) in height. There are five sections within the Alstonia genus: Alstonia, Blaberopus, Dissuraspermum, Monuraspermum, and Tonduzia. The bark, leaves, and sap have many uses in traditional medicine.
These plants feature small, fragrant flowers that may be white, pink, yellow, or green. They mature into dark blue, pod shaped fruits. A. macrophylla, commonly called devil tree, is also called wig banyan in Sri Lanka because the flowers are thought to resemble a woman's long wig.
A. longifolia, the only species growing in Central America, is usually a shrub, but can reach heights of 66 feet (30 meters). A. constricta, commonly called quinine bush or bitterbark, grows only in Eastern Australia and is the only subtropical member of the genus. Its bark is used in homeopathic and traditional medicine to treat dysentery and diarrhea, fever, and parasitic worms. A. angustifolia, native to Indonesia, Malaysia, the Philippines, and Vietnam, is used to treat headache. The sap of various Alstonia species is sometimes used to treat cough, fever, and sore throat, though it is poisonous.
A. scholaris, native to South and Southeast Asia, China, and Australia, is another important medicinal species. Commonly called blackboard tree, Indian devil tree, and pulai, A. scholaris is used to treat malaria, as an alternative to quinine. The bark has also historically been used to treat diarrhea and fever, to promote blood flow, and to heal wounds, while the leaves have been used to treat beriberi.
The wood of A. scholaris is used in coffins in Sri Lanka and for net floats and utensils in Borneo. Other species are used as commercial timber in Indonesia and Malaysia. Timber from plants of the Alstonia section are light, while those of the Dissuraspermum and Monuraspermum sections are heavier.
Some Alstonia species are very rare. A. annamensis grows only in Vietnam and is endangered. A. beatricis is of vulnerable conservation status and grows only in Indonesia. Other vulnerable species are A. breviloba, limited to Papua New Guinea, A. henryi, which grows only in China, and A. penangiana, endemic to Malaysia. A. marquisensis is endemic to French Polynesia, and A. rupestris is endemic to Thailand, but neither of these is a threatened species.