northern China and Korea
Recognizable by the large 1.2–2.0 in thorns on the shoots, and its deciduous leaves with three (or rarely, five) leaflets, typically with the middle leaflet 1.2–2.0 in long, and the two side leaflets 2–3 cm (0.79–1.18 in) long. The flowers are white, with pink stamens, 1.2–2.0 in in diameter, larger than those of true citrus but otherwise closely resembling them, except that the scent is much less pronounced than with true citrus. As with true citrus, the leaves give off a spicy smell when crushed.The fruits are green, ripening to yellow, and 1.2–1.6 in in diameter, resembling a small orange, but with a finely downy surface. (Wikipedia)