Description from Flora of China
Prostrate or erect shrubs or small trees, glabrous, glandular papillate or covered with stellate, villous, or glandular simple or branched trichomes, often with embedded resin cavities protruding from vegetative and floral parts, viscid to resinous. Stipules absent. Leaves simple, alternate to densely spiral, more rarely opposite or whorled, sessile to petiolate; leaf blade margin entire, serrate, crenate, or rarely lobed. Inflorescences a reduced dichasial cyme of 1-12 axillary flowers; bracts absent. Flowers bisexual, rarely functionally male or female. Sepals (4 or)5(or 6-9), distinct, basally connate, or rarely forming a deep calyx tube, valvate or imbricate, ± persistent. Corolla bilabiate, campanulate, rarely urceolate, actinomorphic, or zygomorphic, 5-lobed, lower lip 1-3-lobed, upper lip 2-4-lobed. Stamens 4(-8), inserted in corolla tube, alternate with corolla lobes, included or exserted; filaments filiform; anther cells confluent, reniform or sagittate. Gynoecium of 2 connate carpels; ovary superior, 2-carpelled, becoming 4(-12)-loculed by division of ovary; ovules 1-3(or 4) per locule, pendulous, anatropous; stigma capitate. Fruit usually indehiscent, rarely semi-dehiscent or subschizocarpic, dry or drupaceous with fleshy or watery mesocarp; endocarp woody. Seeds with a straight or slightly curved embryo; endosperm absent or sparse.
The family has recently been monographed (R. J. Chinnock, Eremophila and allied genera: A monograph of the plant family Myoporaceae, 1-672. 2007), and Pentacoelium was re-instated as a genus distinct from Myoporum Banks & Solander ex G. Forster. Although Pentacoelium is comparable vegetatively with species of Myoporum, the flowers are much larger and the fruit are quite different. The fruit of Pentacoelium are large and the most complex in the family. The fruit are similar in size and internal structures to Bontia Linnaeus, a genus endemic to the Caribbean and surrounding coastal areas of South America. Both genera show fruit features that suggest adaptation to dispersal by water, but the fruit of Pentacoelium are more complicated with a star-shaped inner woody zone and up to 10 locules and subapical lacunae extending down into the fruit.
Li Zhenyu. 2002. Myoporaceae. In: Hu Chiachi, ed., Fl. Reipubl. Popularis Sin. 70: 310-313.
Seven genera and ca. 250 species: tropical America, E and SE Asia, Australia, Indian Ocean islands (Mauritius and Rodrigues); one species in China.
(Authors: Hong Deyuan (洪德元); Robert J. Chinnock)