Description from Flora of China
Shrubs or rarely trees, sometimes with short shoots (Gardenia angkorensis, G. sootepensis), unarmed or with short shoots sometimes spinescent, with buds and young stem apices often resinous. Raphides absent. Leaves opposite or rarely ternate, sometimes clustered at stem apices, often with domatia; stipules persistent or deciduous, united shortly around stem or united completely into a conical cap (i.e., calyptrate), triangular or when united into a cap then splitting along one side. Inflorescences pseudoaxillary and/or terminal, fascicled to cymose and several flowered or reduced to 1 flower, pedunculate to sessile, bracteate. Flowers sessile to pedicellate, bisexual, monomorphic, often showy. Calyx with ovary portion well developed and often longitudinally ridged; limb 5-8-lobed or sometimes fused into a tube or conical cap that splits irregularly as corolla elongates (i.e., spathaceous), often well developed. Corolla white to cream, salverform or funnelform, glabrous or variously pubescent inside; lobes 5-12, convolute in bud. Stamens 5-12, inserted in corolla throat, included or partially exserted; filaments very short or reduced; anthers dorsifixed. Ovary 1-celled, ovules numerous on 2-6 parietal placentas; stigma clavate or 2-lobed, included or exserted. Fruit generally yellow to orange, red-orange, or brown with pulp usually orange, baccate, leathery or fleshy, ellipsoid to subglobose, smooth or with longitudinal ridges, with calyx limb usually persistent or sometimes upper part tardily deciduous; seeds numerous, medium-sized, ellipsoid, compressed, embedded in pulp; testa leathery or membranous; endosperm usually corneous; embryo small or medium-sized; cotyledons broad, leaflike.
The persistent calyx lobes apparently enlarge markedly as the fruit develop in many species; this may be confusing when the enlarged fruiting calyx lobes are compared with descriptions of flowering calyx lobes. The flowers are often nocturnal and are usually strongly sweetly fragrant with an odor of, well, gardenia. Several species from Asia and the Pacific are occasionally cultivated, but Gardenia jasminoides---native to our region---is very popular worldwide for its flowers.
About 60-200 or 250 species: tropical and subtropical regions of Africa, Asia, Madagascar, and Pacific islands; five species (one endemic) in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)