Commonly known as trifoliate orange, is a cold-hardy, deciduous citrus relative native to northern and central China. Although historically grouped within the citrus family, it is botanically distinct enough to be placed in its own genus, Poncirus, and is the most cold-tolerant citrus relative known, surviving temperatures as low as −20 °C to −25 °C once fully dormant. The tree is immediately recognizable by its trifoliate leaves, large thorns, and deciduous habit, shedding its leaves completely in winter—an adaptation unique among citrus relatives and a major contributor to its extreme cold hardiness. In spring, it produces fragrant white flowers similar to true citrus, followed by small, round, yellow fruits in autumn. The fruit is extremely bitter and resinous, containing high levels of poncirin and other compounds that make it undesirable for fresh eating.