Citrus Linn., Sp. Pl. 782. 1753. Gen. Pl. ed. 5341.1754; Hook. f., Fl. Brit. Ind. 1:514.1875; Tanaka, Sp. Problem in Citrus, Revisio Aurantiacearum, ix. 1-140.1954; Townsend in Davis, Fl. Turk. 2:507.1967; id. in Tutin et al., Fl. Eur. 2:229.1968.
Evergreen, small trees or shrubs, often spiny. Leaves simple, alternate, glandular punctate, petiole winged or margined. Flowers perfect or staminate, solitary or clustered in axillary racemes. Calyx 4-5-lobed, glabrous or pubescent. Petals (4-) 5(-8). Stamens 4-10 times the petals, polyadelphous. Ovary 10-14-locular, ovules biseriate or collateral. Fruit a fleshy hesperidium, globose to mamillate-oblong to oblate, rind tight or loose, with oil glands. Seeds embedded in pulpy vesicles.
Most or all of the species are cultivated, derived from the native species of tropical and subtropical regions of SE. Asia. Because of its great economic importance, domestication, cultivation and hybridization of the species has led to many varieties and forms, thus providing taxonomic problems. The following account of the species is primarily based on the work of Tanaka & Swingle with modifications in the treatment of the varieties.
Tanaka has described over 100 species. A genus widely cultivated. 10 species have been described from Pakistan.
