Trigonostemon Blume

Timothy M. A. Utteridge and Laura V. S. Jennings (2022). Trees of New Guinea. Kew Publishing. Royal Botanic Gardens, Kew

Distribution

A genus of up to 60 species from India and Sri Lanka throughout Indo-China and Malesia to New Guinea and Queensland; two species in New Guinea, one of which just reaches the size to be considered a small tree (T. hartleyi Airy Shaw).

Morphology General Habit

Shrubs or small trees to 4 m (in New Guinea) Plants monoecious

Morphology General

Sap sometimes present, red or orange, latex absent

Morphology Leaves Stipules

Stipules minute, triangular or subulate, caducous

Morphology Leaves

Leaves spiral at the end of the branches, alternate or subopposite, margins entire to crenate, usually triplinerved at the base (in New Guinea)

Morphology Reproductive morphology Inflorescences

Inflorescences cymose to raceme-like, axillary or terminal, uni- or bisexual-Flowers: sepals 5; petals 5, often brightly coloured (dark purplish red, red, orange-yellow or white), usually drying blackish; disk glands 5, usually united into a ring or cup. Staminate flowers: stamens 3 or 5, filaments united, but apically spreading; pistillode absent

Morphology Reproductive morphology Flowers Gynoecium Pistil

Pistillate flowers: ovary 3-locular; style bifid or twice bifid

Morphology Reproductive morphology Fruits

Fruit a capsule, 3-lobed, smooth, glabrous or pubescent, splitting into 3 bivalved parts, calyx persistent, sometimes enlarged

Morphology Reproductive morphology Seeds

Seeds globose; caruncle absent.

Ecology

Species of Trigonostemon have been collected from lowland forest up to 150 m elevation.

Recognition

The genus can be recognised by the low habit (never medium or large trees), leaves usually clustered at the ends of the branches, usually triplinerved from the base, the staminate flowers with brightly coloured petals and 3–5 stamens.