Description from Flora of China
Trees or erect or scandent shrubs. Branches and branchlets lenticellate. Leaves opposite, rarely alternate or whorled, simple, trifoliolate, or pinnately compound, without stipules; venation pinnate or palmate. Inflorescences terminal or axillary, in cymes, panicles, racemes, umbels, or fascicles. Flowers actinomorphic, bisexual, rarely unisexual or polygamous and plants monoecious, dioecious, or polygamodioecious. Calyx 4(-16)-lobed or -parted, rarely absent. Corolla 4(-16)-lobed, sometimes almost free to base, rarely absent; lobes sometimes united in pairs at base or into a very short tube. Stamens 2(-4), inserted on corolla tube or hypogynous; anthers dehiscing longitudinally; pollen 3-colpate or 3-colporate. Ovary superior, 2-loculed; ovules 2 in each locule, sometimes 1 or numerous. Style 1 or absent; stigma 2-lobed or capitate. Fruit a drupe, berry, capsule, or samara. Seeds with straight embryo, with or without endosperm; radicle curved upward or downward.
About 28 genera and over 400 species: tropical, subtropical, and temperate regions of world, but mainly in Asia. China has 10 genera and 160 species (95 endemic) and is the center of diversity for the genera Forsythia, Syringa, Osmanthus, and Ligustrum.
Many genera are important economically: Fraxinus and Forsythia (medicinal, ornamental); Jasminum, Osmanthus, and Syringa (spice, ornamental); Olea (oil); and Fraxinus (timber).
Chang Mei-chen, Miao Bo-mao, Lu Rui-ling, & Qiu Lian-qing in: Chang Mei-chen & Qiu Lian-qing, eds. 1992. Oleaceae. Fl. Reipubl. Popularis Sin. 61: 1-222.
(Authors: Chang Mei-chen, Qiu Lian-qing, Wei Zhi; Peter S. Green)