Ackama A.Cunn.

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

Distribution

Ackama is a genus of 10 species in total that occur in Australia and New Zealand (two species endemic to each), five endemic to New Guinea plus one that occurs from the Philippines to the Solomon Islands. The species in Malesia and the Solomon Islands were previously placed in Spiraeopsis Miq. and before that in Caldcluvia D.Don (which now  includes only a single species from South America).

Morphology General Habit

Trees and shrubs to 40 m tall

Morphology Leaves Stipules

Stipules interpetiolar, 1 pair per node, orbicular or reniform

Morphology Leaves

Leaves opposite and decussate, imparipinnate with 5–9 leaflets, lateral leaflets opposite or subopposite, coriaceous, undersurface sometimes densely hairy, indumentum often including stellate hairs and orange orbicular trichomes, domatia frequently present on undersurface of leaves

Morphology Reproductive morphology Inflorescences

Inflorescences axillary, paniculate, branching pattern initially opposite, becoming alternate

Morphology Reproductive morphology Flowers

Flowers bisexual but strongly protandrous, 4–5-merous; calyx lobes valvate; petals elliptic, equal in length to calyx, caducous; stamens at least twice as long as petals; ovary superior, syncarpous, 2–5-locular, ovules 6–16 per locule, stigma punctate. Fruit a capsule with as many valves as locules, margins of valves often detaching from the main part of the valve but remaining connate with margins of adjacent valves, forming a replum

Morphology Reproductive morphology Seeds

Seeds few per fruit, winged at both ends.

Ecology

In New Guinea, Ackama is found in primary and secondary forests from the lowlands to the subalpine zone, between 250–3300 m, but most often in lower montane forests.

Recognition

In New Guinea, Ackama commonly has a dense indumentum on the inflorescences and leaf undersides, which is often orange when dry and generally includes stellate hairs. The genus can be recognised by its orbicular stipules, the coriaceous, imparipinnate leaves, the protandrous flowers with petals, the 2–5-locular ovary and the capsular fruit.