Citrus cavaleriei

Citrus cavaleriei, the Ichang papeda (Chinese: 宜昌橙), is a slow-growing species of papeda that has characteristic lemon-scented foliage and flowers. It is native to southwestern and west-central China and is likely named for the city of Yichang (宜昌), in China's Hubei province. The Ichang papeda is notable for its unusual hardiness. With the exception of Poncirus trifoliata, it is the hardiest citrus plant, tolerating both moderate frost and damp conditions....read more on Wikipedia.