Ongzi's SecretGarden: Alstonia in Malesia

Tuesday, 27 August 2019

Alstonia in Malesia

Alstonia is a widespread genus of evergreen trees and shrubs, of the dogbane plant family Apocynaceae. It consists of about 40-60 species, native to tropical and subtropical Africa, Central America, southeast Asia, Polynesia and Australia.

Nomeclature¹

Alstonia was named by Robert Brown in 1811, after Charles Alston (1685–1760), a professor of botany at Edinburgh from 1716-1760.

Description¹

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.

Sections^1&2

Alstonia has 5 distinct sections, each a monophyletic group; Alstonia ( including Winchia ), Blaberopus, Tonduzia. Monuraspermum, and Dissuraspermum.

Species of the section Memuraspermum have no latex in the trunk bark, in contrast to the species of section Alstonia, where latex may be observed in all parts of the plant.

The leaves of Alstonia are opposite or whorled. Opposite leaves are found in most species of Dissuraspermum. Worled leaves are found in the other sections.