Alstonia R.Br.

Scientific Description

Family Apocynaceae.

Habit and leaf form. Trees, or shrubs (not in Australia); evergreen; laticiferous (white). Plants unarmed. Leaves cauline. To 10–35 m high (in trees). Mesophytic. Not heterophyllous. Leaves medium-sized to large; opposite, or whorled; 3–7 per whorl; leathery, or membranous; petiolate; simple. Leaf blades dorsiventral; entire; linear, or ovate, or obovate, or elliptic; pinnately veined; cuneate at the base. Mature leaf blades adaxially glabrous, or pubescent (with basifixed hairs); abaxially glabrous, or pubescent (with basifixed hairs). Leaves without stipules. Leaf blade margins entire. Leaf anatomy. Hairs present; glandular hairs absent. Unicellular hairs absent. Complex hairs present. Branched hairs absent. Complex hairs peltate.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; in cymes, or in panicles. Inflorescences compound; terminal. Flowers pedicellate; bracteate; small; more or less fragrant; regular; 5 merous; tetracyclic. Hypogynous disk present; annular. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed (lobes are deeply divided); lobulate. Calyx lobes markedly longer than the tube. Calyx erect; hairy; exceeded by the corolla; regular; green. Calyx lobes ovate, or obovate. Corolla present; 5; 1 -whorled; gamopetalous; lobed (lobes spreading); lobulate. Corolla lobes markedly shorter than the tube. Corolla contorted (sinistrorse or dextrorse in bud); hypocrateriform (corolla tube swollen about the stamens); regular; glabrous abaxially (commonly), or hairy abaxially; hairy adaxially; plain; white, or cream, or yellow. Corolla lobes oblong, or ovate. Androecial members definite in number. Androecium 5. Androecial members adnate (epipetalous;); all equal; free of one another; 1 -whorled. Stamens 5. Staminal insertion midway down the corolla tube, or in the throat of the corolla tube. Stamens all inserted at the same level; remaining included; all more or less similar in shape; isomerous with the perianth; oppositisepalous; all alternating with the corolla members. Anthers all alike; dehiscing via longitudinal slits. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous (the carpels united only by their styles); eu-syncarpous; superior. Ovary plurilocular; 2 locular. Gynoecium stylate. Styles 1; hairless. Stigmas 1. Placentation axile. Ovules 2–50 per locule (‘many’).

Fruit and seed features. Fruit 70–405 mm long; non-fleshy; a schizocarp. Mericarps comprising follicles (2). Dispersal unit the seed. Fruit 30–50 seeded (‘many’). Seeds compressed (oblong); small; conspicuously hairy (browns hairs around the entire margin); with a tuft of hairs (at the ends); wingless.

Geography, cytology, number of species. World distribution: Africa, Asia, Malesia, Melanesia and Australia. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, Queensland, and New South Wales. Northern Botanical Province. A genus of 45–50 species; 3 species in Western Australia; 1 endemic to Western Australia.

Additional comments. Etymology: named for Dr. C. Alston (1685–1760), Professor of Botany at Edinburgh University, Scotland.

Etymology. After Charles Alston (1685–1760), Scottish physician and professor of botany at Edinburgh 1716–60.