Alphitonia is a genus of about 15 species of trees and shrubs in the buckthorn family Rhamnaceae (order Rosales). The genus ranges across tropical Southeast Asia, Oceania, and Polynesia, with its greatest diversity in Australia, New Guinea, and the southwestern Pacific islands.
Members of the genus are typically medium to large trees, though some species are shrubby. The leaves are lanceolate, leathery (coriaceous), and alternate, reaching about 12 cm in length. Leaf margins are smooth, venation is pinnate, and the undersurface bears white to rusty complex hairs. Stipules are present and the petiole is short relative to the blade. The small bisexual flowers are borne in terminal or axillary clusters and produce creamy blossoms in spring. Each flower has 5 sepals, 5 petals, and 5 stamens, with a hypanthium and an inferior ovary. The fruits are ovoid, blackish, non-fleshy capsules, each locule containing a single seed.
Several Australian species are colloquially known as "ash trees" or "sarsaparilla trees," though Alphitonia is unrelated to the true ashes (Fraxinus, family Oleaceae) or to sarsaparilla vines (Smilax, a monocot). In Australia, notable species include Alphitonia excelsa (red ash or soap tree), A. petriei (pink ash), and A. whitei (red ash). Alphitonia ponderosa, known as kauila, is native to Hawaiʻi and is culturally significant there.
The genus has an interesting ecological relationship with the hepialid moth Aenetus mirabilis, whose larvae feed exclusively on Alphitonia trees, boring horizontally into the trunk before tunneling vertically downward.
Alphitonia was described by Reissek ex Endl. (1840) and is named from the Greek álphiton (ἄλφιτον), meaning "barley-meal," a reference to the mealy texture of the fruit mesocarp.
Etymology
The genus name Alphitonia derives from the ancient Greek álphiton (ἄλφιτον), meaning "barley-meal." This alludes to the mealy quality of the fruits' mesocarps; an alternative interpretation holds that "baked barley meal" refers to the mealy red covering around the hard cells within the fruit.
Distribution
Alphitonia species occur in tropical regions of Southeast Asia, Oceania, and Polynesia. The genus is represented in Australia (where several species are widespread), New Guinea, New Caledonia, the Solomon Islands, Fiji, Tonga, Samoa, the Marquesas, Hawaiʻi, and various other Pacific island groups including the Cook Islands, Society Islands, Vanuatu, and Wallis & Futuna.
Ecology
Alphitonia trees are the exclusive larval host plant of the hepialid moth Aenetus mirabilis. The caterpillars bore horizontally into the trunk before turning to tunnel vertically downward, a feeding strategy found on no other host plants.
