Alphitonia Reissek ex Endl.

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

Distribution

A genus of c. 15 species from Malaysia through to the Pacific Islands including Hawaii; six species in New Guinea.

Morphology General Habit

Shrubs or trees to 40 m, unarmed. Stipules subulate, caducous

Morphology Leaves

Leaves alternate, ovate to obovate or elliptic to lanceolate, papery to leathery, pinnately veined, adaxially usually glabrous, abaxially whitish to rusty pubescent, margins entire

Morphology Reproductive morphology Inflorescences

Inflorescences axillary or rarely terminal, di- or trichotomous cymes

Morphology Reproductive morphology Flowers

Flowers bisexual, 5-merous; calyx tube patelliform to hemispherical, lobes triangular, adaxially keeled; petals 5, clawed, cucullate; stamens 5, enfolded by the petals; disk mainly thick, nectariferous; ovary inferior, immersed in the disk, (2–)3-loculed, 1 ovule per locule, style short, often divided into 2 to 3 slightly capitate stylar branches

Morphology Reproductive morphology Fruits

Fruits sometimes capsular then schizocarpically dehiscent, initially appearing drupaceous, globose or broadly ovoid or sometimes large and strongly beaked (A. macrocarpa), with latterly dehiscent endocarp, base surrounded by persistent calyx tube; pericarp initially fleshy, later dry and mealy, endocarp hard, leathery, splitting longitudinally usually along 3 ventral sutures

Morphology Reproductive morphology Seeds

Seeds usually 3, persistent on the torus after endocarp dehiscence, covered with a membranous, reddish to brownish aril; testa smooth, crustaceous.

Ecology

Alphitonia species can be found in primary lowland rain forests and in secondary regrowth areas from sea level to 2500 m.

Recognition

Members of the genus can be recognised by the alternate entire leaves which are usually strongly discolourous, i.e. the lower surface is often very pale, almost white, due to the dense covering of hairs. The fruits are dehiscent with the endocarps, or ‘stones’, dehiscing at maturity, but initially the fruits have a fleshy pericarp which matures to a dark-purple to black before becoming mealy and dehiscing, leaving the seeds hanging on the receptacle; the seeds appear red due to the aril. Note, Hopkins et al. (2015) discuss the fruit structure of the genus in some details, especially with regard to the strongly beaked fruits of A. macrocarpa Mansf. found in New Guinea. The genus is very close to Emmenosperma and was considered related to Colubrina because of the type of fruit dehiscence, however, Alphitonia differs in the number of locules from the former, and the seeds persisting on the receptacle from the latter.