This is the hardiest close relative of Citrus. It is a deciduous shrub armed with vicious spines and will survive temperatures as low as 0F to -10F. In the USA it certainly grows as far north as Boston, MA (Hardy for zones 5-9). The fruits are like small oranges about 1.5 inches across, very sour, but can be used in conserves and drinks. Watch it through the seasons. In spring it sports white, fragrant flowers. Its summer foliage is shiny and dark green. In autumn it sheds its leaves to show off its glossy-green stems. Fruit, which is very sour, also adds fall interest. It is a great barrier plant and can be trimmed to form a 3-foot hedge. It can also be used as a novelty specimen. It is also used as citrus rootstock.