Alstonia is a widespread genus of evergreen trees and shrubs, of the family Apocynaceae. It was named by Robert Brown in 1811, after Charles Alston (1685–1760), professor of botany at Edinburgh from 1716 to 1760.

The type species Alstonia scholaris (L.) R.Br. was originally named Echites scholaris by Linnaeus in 1767.

Description

Alstonia consists of about 40–60 species (according to different authors) native to tropical and subtropical Africa, Central America, Southeast Asia, Polynesia and Australia, with most species in the Malesian region.

These trees can grow very large, such as Alstonia pneumatophora, recorded with a height of 60 m and a diameter of more than 2 m. Alstonia longifolia is the only species growing in Central America (mainly shrubs, but also trees 20 m high).

The leathery, sessile, simple leaves are elliptical, ovate, linear or lanceolate and wedge-shaped at the base. The leaf blade is dorsiventral, medium-sized to large and disposed oppositely or in a whorl and with entire margin. The leaf venation is pinnate, with numerous veins ending in a marginal vein. Phyllotaxy is whorled i.e. two or more leaves arises at a node and form a whorl .

The inflorescence is terminal or axillary, consisting of thyrsiform cymes or compound umbels. The small, more or less fragrant flowers are white, yellow, pink or green and funnel-shaped, growing on a pedicel and subtended by bracts. They consist of 5 petals and 5 sepals, arranged in four whorls. The fertile flowers are hermaphrodite. The gamosepalous green sepals consist of ovate lobes, and are distributed in one whorl. The annular disk is hypogynous. The five gamesepalous petals have oblong or ovate lobes and are disposed in one whorl. The corolla lobes overlapping to the left (such as A. rostrata) or to the right (such as A. macrophylla) in the bud. The ovary has 2 separate follicles with glabrous or ciliate, oblong seeds that develop into deep blue podlike, schizocarp fruit, between 7–40 cm long. The plants contain a milky latex, rich in poisonous alkaloids. Fijians use the latex of A. costata (saurua, sorua) as a form of chewing gum. The Alstonia macrophylla is commonly known in Sri Lanka as 'Havari nuga' or the 'wig banyan' because of its distinct flower that looks like a woman's long wig.

Alstonia trees are used in traditional medicine.

Many Alstonia species are harvested for timber, called pule or pulai in Indonesia and Malaysia. Trees from the section Alstonia produce lightweight timber, while those from the sections Monuraspermum and Dissuraspermum produce heavy timber.

Alstonia trees are widespread and mostly not endangered. However a few species are very rare, such as A. annamensis, A. beatricis, A. breviloba, A. stenophylla and A. guangxiensis.

Species Alstonia has five distinct sections, each a monophyletic group; Alstonia, Blaberopus, Tonduzia, Monuraspermum, Dissuraspermum.

, Plants of the World Online accepts the following 44 species: Alstonia actinophylla (A.Cunn.) K.Schum. – milkwood - New Guinea, N Australia Alstonia angustifolia A.DC. - Borneo, W Malaysia, Sumatra Alstonia angustiloba Miq. - Borneo, W Malaysia, Sumatra, Thailand, Java Alstonia annamensis (Monach.) K.Sidiyasa - Cambodia, Vietnam Alstonia balansae Guillaumin - New Caledonia Alstonia beatricis K.Sidiyasa - Waigeo I in E Indonesia Alstonia boonei De Wild. - W + C + E Africa Alstonia boulindaensis Boiteau - New Caledonia Alstonia breviloba K.Sidiyasa - Papua New Guinea Alstonia congensis Engl. - W + C Africa Alstonia constricta F.Muell. – bitterbark, quinine tree, Australian fever bark - E Australia Alstonia coriacea Pancher & S.Moore - New Caledonia Alstonia costata R.Br. - S Pacific Alstonia curtisii King & Gamble - Thailand Alstonia deplanchei Van Heurck & Müll.Arg. - New Caledonia Alstonia guangxiensis D.Fang & X.X.Chen - Guangxi in China Alstonia iwahigensis Elmer - Borneo, Palawan Alstonia lanceolata Van Heurck & Müll.Arg. - New Caledonia Alstonia lanceolifera S.Moore - New Caledonia Alstonia legouixiae Van Heurck & Müll.Arg. - New Caledonia Alstonia lenormandii Van Heurck & Müll.Arg. - New Caledonia Alstonia longifolia (A.DC.) Pichon - Mexico, Central America Alstonia macrophylla Wall. ex G.Don – batino, devil tree - S China, Sri Lanka, SE Asia, New Guinea Alstonia mairei H. Léveillé - S China, N Vietnam Alstonia muelleriana Domin – jackapple, leatherjacket, milky yellowwood - New Guinea, Queensland Alstonia neriifolia D.Don - Nepal, Sikkim, Bhutan Alstonia odontophora Boiteau - New Caledonia Alstonia parkinsonii (M.Gangop. & Chakrab.) Lakra & Chakrab. - Andaman Is. Alstonia parvifolia Merr. - Philippines Alstonia penangiana K.Sidiyasa - Penang Hill in Malaysia Alstonia pneumatophora Backer ex L.G.Den Berger - W Malaysia, Borneo, Sulawesi, Sumatra Alstonia quaternata Van Heurck & Müll.Arg. - New Caledonia Alstonia rostrata C.E.C.Fischer - Yunnan, Indochina, W Malaysia, Sumatra Alstonia rubiginosa K.Sidiyasa - Papua New Guinea Alstonia rupestris Kerr - Thailand Alstonia scholaris (L.) R.Br. – pali-mari, dita bark, bitter bark, milkwood, milky bean, milky pine, white cheesewood, scholar tree, blackboard tree - E + S + SE Asia, Papuasia, N Australia Alstonia sebusii (Van Heurck & Müll.Arg.) Monach. - Yunnan, Bhutan, Assam, N Myanmar Alstonia spatulata Blume – hard milkwood, Siamese balsa - SE Asia, New Guinea Alstonia spectabilis R.Br. – poele bark, jackapple, leatherjacket, milky yellowwood - SE Asia, Papuasia, N Australia Alstonia sphaerocapitata Boiteau - New Caledonia Alstonia venenata R.Br. - S India Alstonia vieillardii Van Heurck & Müll.Arg. - New Caledonia Alstonia vietnamensis D.J.Middleton - Vietnam Alstonia yunnanensis Diels - Yunnan, Guizhou, Guangxi

Gallery

References

Kade Sidiyasa, A., 3, 1992. A monograph of Alstonia (Apocynaceae).