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(Poncirus trifoliata), the only species of the plant genus Poncirus of the family Rutaceae. A strongly branched small tree reaching 3 m in height, the trifoliate orange has deciduous trifoliate leaves and strong, sharp axillary thorns. The flowers are bisexual, white, and odorless; they are axillary and appear singly or in pairs. Flowering occurs before the leaves open. The greenish yellow spherical fruits are small, measuring 3–5 cm in diameter. They are many-seeded and have a bitter pulp. The rind is aromatic, slightly pubescent, and quite thick. The juice contains about 5 percent citric acid.
The trifoliate orange grows in North China. In the USSR it is raised in regions where citrus crops are grown as stocks. The plant tolerates brief frosts to – 25°C. Propagation is by seed. The trifoliate orange is used in selective breeding for developing more winter-hardy intergenus and interspecies hybrids of citrus crops.