Decaspermum J.R.Forst. & G.Forst.

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

Distribution

A genus of 34 species, distributed from South-East Asia to the Pacific; 16 species (nine endemic) in New Guinea, a single endemic species in the Solomon Islands.

Morphology General Habit

Lowland and forest trees and montane shrubs

Morphology Leaves

Leaves opposite, chartaceous in lowland species to coriaceous in montane species, elliptic to ovate, 4–80 mm long, apex acute or acuminate, pinnately veined, intramarginal vein visible, often with silky pubescence on young growth, mature leaves glabrous

Morphology Reproductive morphology Inflorescences

Inflorescences very varied, terminal or axillary, in lowland species panicles or racemes, in montane species 3-flowered dichasia or flowers solitary

Morphology Reproductive morphology Flowers

Flowers bisexual, occasionally staminate, 4–5-merous, hypanthium not extending above the ovary; calyx lobes free, much smaller than the petals, persistent in fruit; petals white or pink; stamens free, many, filaments slender; ovary inferior, (3–)4–5(–10)-locular style slender, filiform, stigma capitate or peltate

Morphology Reproductive morphology Fruits

Fruit a berry, globose, vertically ribbed

Morphology Reproductive morphology Seeds

Seeds 2 per locule, separated by a false septum; embryo horseshoe-shaped, cotyledons much shorter than the radicle.

Ecology

In New Guinea, Decaspermum can be found from sea level coastal forests to subalpine grasslands to 3675 m.

Recognition

The growth form, leaf size and texture, inflorescence and locule number varies considerably between the species. Characters to distinguish the genus are: the pink or white flowers with a capitate stigma, the usually 4–5-locular ovary, the ribbed fruit and the false septa between the seeds of each locule. The larger leaved lowland species can be distinguished from Syzygium by the silky hairs covering the young parts of the plant. The smaller leaved montane species can be distinguished from Xanthomyrtus and Uromyrtus by their erect white or pink flowers (flowers yellow in Xanthomyrtus and nodding in Uromyrtus).