Wagner, Warren L., Derral R. Herbst and S. H. Sohmer. 1999. Manual of the Flowering Plants of Hawai'i (Bernice Pauahi Bishop Museum Special Publication, 2 Vol. Set). Honolulu, HI

Flora of Hawaii:

Distribution     
Native from eastern Africa, India, Taiwan, and Malesia to Australia and the Tuamotus. In the Hawaiian Islands, a Polynesian introduction on Kaua`i, O`ahu, Moloka`i, Lana`i, Maui, Hawai`i.

Habit
Large trees 8-25 m tall with milky sap, trunk massive, to 1.5 m in diam., bark deeply fissured.

Leaves
Leaves chartaceous or somewhat coriaceous; blade broadly elliptic to obovate elliptic, 11-20 cm long, 5.5-9 cm wide, lateral veins arising at a 70° angle or more from midrib, apex rounded or notched; petiole 1-3 cm long.  

Flowers
Flowers in axillary, racemose or paniculate inflorescences, pedicels 2-6 cm long; sepals 4, outer ones 4-6 mm long, inner ones reflexed and slightly longer, petaloid; petals 4(-8), white, 8-14 mm long; ovary reddish purple after pollination, globose; style often s-shaped; stamens yellow.  

Fruit
Fruit green ripening yellowish brown or dark brown, broadly ellipsoid to subglobose, 2-3(-5) cm in diam., pulp 3-5 mm thick.  

Seeds
Seed subglobose-ellipsoid, 2-2.5 cm in diam., testa with spongy outer layer 1-12 mm thick.  

Chromosomes
2n = 32.  

Notes
A Polynesian introduction, now occasionally cultivated. Seeds yield oil of tamanu, used for general skin and cosmetic purposes.