Citrus ichangensis

Known as the Ichang lemon, citrus ichangensis is a slow-growing species with the characteristic lemon-scented foliage and flowers of the lemon family. Its main claim to fame is its unusual hardiness. With the exception of poncirus trifoliata (which is not generally regarded as a true citrus), it is the hardiest of the citrus family, tolerating both moderate frost and damp conditions. For this reason, it is perhaps the only species of true citrus which can be reliably grown outside in temperate areas of Europe and the United States.