Description from Flora of China
Citrus ×aurantium Linnaeus f. deliciosa (Tenore) Hiroe; C. ×aurantium var. tachibana Makino; C. daoxianensis S. W. He & G. F. Liu; C. deliciosa Tenore; C. depressa Hayata; C. erythrosa Yu. Tanaka; C. madurensis Loureiro var. deliciosa (Tenore) Sagot; C. mangshanensis S. W. He & G. F. Liu; C. ×nobilis Loureiro subf. deliciosa (Tenore) Hiroe; C. ×nobilis var. deliciosa (Tenore) Guillaumin; C. ×nobilis subf. erythrosa (Yu. Tanaka) Hiroe; C. ×nobilis var. major Ker Gawler; C. ×nobilis var. ponki Hayata; C. ×nobilis subf. reticulata (Blanco) Hiroe; C. ×nobilis var. spontanea Ito; C. ×nobilis subf. succosa (Tanaka) Hiroe; C. ×nobilis var. sunki Hayata; C. ×nobilis subf. tachibana (Makino) Hiroe; C. ×nobilis var. tachibana (Makino) Ito; C. ×nobilis subf. unshiu (Marcowicz) Hiroe; C. ×nobilis var. unshiu (Marcowicz) Tanaka ex Swingle; C. ×nobilis var. vangasy (Bojer) Guillaumin; C. ponki Yu. Tanaka; C. poonensis Yu. Tanaka; C. reticulata var. austera Swingle; C. reticulata subsp. deliciosa (Tenore) Rivera et al.; C. reticulata subsp. tachibana (Tanaka) Rivera et al.; C. reticulata subsp. unshiu (Marcowicz) Rivera et al.; C. succosa Tanaka; C. suhuiensis Hayata; C. sunki Tanaka; C. tachibana (Makino) Yu. Tanaka; C. tachibana subf. depressa (Hayata) Hiroe; C. tachibana subf. ponki (Hayata) Hiroe; C. tachibana subf. suhuiensis (Hayata) Hiroe; C. tachibana subf. sunki (Hayata) Hiroe; C. tangerina Yu. Tanaka; C. tankan Hayata; C. unshiu Marcowicz; C. vangasy Bojer.
Small trees. Branchlets numerous, with few spines. Leaves 1-foliolate; leaf blade lanceolate, elliptic, or broadly ovate, basal articulated part to leaf blade usually narrow or only a remnant, midvein furcate near apex, margin apically obtusely crenulate or rarely entire, apex emarginate. Flowers solitary to 3 in a fascicle. Calyx irregularly 3-5-lobed. Petals usually 1.5 cm or less. Sta-mens 20-25. Style long, slender; stigma clavate. Fruit pale yellow, orange, red, or carmine, oblate to subglobose, smooth or coarse; pericarp very thin to thick, easily removed; sarcocarp with 7-14 segments or rarely more, sweet to acidic and sometimes bitter, with few to many seeds or rarely seedless; pulp vesicles plump, short, rarely slender and long. Seeds usually ovoid, base rounded, apex narrow and acute; embryos numerous, rarely solitary; cotyledons dark green, pale green, or milky white; chalaza purple. Fl. Apr-May, fr. Oct-Dec. 2n = 18, 27, 36.
Tangerine or mandarin orange is the parent with Citrus maxima of C. ×aurantium, with C. japonica of C. ×microcarpa, and possibly with C. cavaleriei of C. ×junos. The recently recognized subspecies are perhaps better considered as cultivar groups to which most of the synonyms would be referred. However, some names in the synonymy may be referable to those cultivars of C. ×aurantium that are repeated backcrosses with C. reticulata. Trees referred to C. tachibana may represent true wild forms and have the following characteristics:
Trees to 3 m tall. Branchlets numerous, with short spines. Petiole 8-10 mm, very narrowly winged; leaf blade elliptic, 6-7 × 3.5-4 cm, secondary veins inconspicuous, base broadly cuneate, margin crenulate, apex narrow, obtuse, and conspicuously emarginate. Flowers solitary, 1.2-1.4 cm in diam.; flower buds subglobose. Pedicel ca. 2 mm. Petals white. Stamens ca. 20. Fruit yellow, oblate, 2-2.5 × 2.5-3.4 cm, smooth; pericarp 1.5-2 mm thick; sarcocarp with 7-9 segments, yellow, very acidic and bitter, 5- or 6-seeded. Seeds broadly ovoid, ca. 1 cm; seed coat smooth; embryos numerous; cotyledons greenish.
Extensively cultivated in China S of the Qin Ling [possibly native to SE China and/or S Japan (see below)].
Hillside forests; low elevations. Taiwan [Japan (Ryukyu Islands)].