The longan (Cantonese long-ngan; literally "dragon eye"; Thai ลำไย) is a tropical tree native to southern China. It is also found in Southeast Asia. It is also called guiyuan (桂圓) in Chinese, lengkeng in Indonesia, mata kucing (literally "cat's eye") in Malaysia, nhãn in Vietnamese (The Species: Euphoria longana Lamk. named "long nhãn" in Vietnamese- literally "dragon's eyes"), Mora in Sinhalese (Sri Lanka) and also "longan" in Tagalog.
The longan ("dragon eyes") is so named because of the fruit's resemblance to an eyeball when it is shelled (the black seed shows through the translucent flesh like a pupil/iris). The seed is small, round and hard.
To express longan fruit, Vietnamese has a wonder: Da cóc mà bọc bột lọc, bột lọc mà bọc hòn than (literally: Toad's skin covers tapioca wheat, tapioca wheat covers coal ball): toad's skin is the ugly skin, tapioca wheat is the clear white flesh and coal ball is the black seed.
The fruit is edible, and is often used in East Asian soups, snacks, desserts, and sweet-and-sour foods, either fresh or dried, sometimes canned with syrup in supermarkets. The seeds of fresh longan can be boiled and eaten, with a distinctive nutty flavor.
Dried longan are often used in Chinese cuisine and Chinese sweet dessert soups. In Chinese food therapy and herbal medicine, it is believed to have an effect on relaxation. In contrast with the fresh fruit, which is juicy and white, the flesh of dried longans is dark brown to almost black. In Chinese medicine the longan, much like the lychee, is considered a "warm" fruit.