Xanthostemon F.Muell.

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

Distribution

About 50 species, Malesia to the south-western Pacific, about four species in New Guinea (two endemic), one endemic species in the Solomon Islands.

Morphology General Habit

Trees and shrubs to 15 m tall

Morphology Leaves

Leaves always alternate when young, alternate or occasionally opposite when mature, coriaceous, elliptic to lanceolate, often rounded or revolute at the tip, pinnately veined with an obvious intra-marginal vein

Morphology Reproductive morphology Inflorescences

Inflorescences axillary, in few-flowered cymes, thyrses or panicles, occasionally flowers solitary

Morphology Reproductive morphology Flowers

Flowers 4–5-merous, all parts uniform in colour, yellow, white or red; calyx lobes free, acute or truncate, longer than broad, persistent in fruit; petals free, rounded; stamens many, free, at least twice as long as the petals; style long and slender, longer than the stamens, base persistent until capsule dehisces; ovary semi-inferior to almost superior, 3–5-locular; placentation axile, ovules numerous

Morphology Reproductive morphology Fruits

Fruit a globose, woody loculicidal capsule

Morphology Reproductive morphology Seeds

Seeds numerous, flattened and occasionally winged.

Ecology

In New Guinea, Xanthostemon has been recorded from lowland rain forests and savannahs to 500 m.

Recognition

Characters that distinguish Xanthostemon are a robust habit, coriaceous leaves rounded at the apex, inflorescences which have an axis that branches several times, yellow or red flowers with free stamens that are at least twice as long as the petals. Metrosideros, which also has coriaceous leaves, red flowers with much exserted stamens and capsular fruit can be distinguished from Xanthostemon by its opposite leaves, scaly vegetative buds and inflorescences which are often ramiflorous and with an unbranched axis.