Citrus unshiu is a seedless and easy-peeling citrus species, also known as unshu mikan, cold hardy mandarin, satsuma mandarin. It is of Chinese origin, named after Unsyu (Wenzhou), China, but introduced to the West via Japan.
One of the English names for the fruit, satsuma, is derived from the former Satsuma Province in Japan, from which these fruits were first exported to the West.
Under the Tanaka classification system, Citrus unshiu is considered a separate species from the mandarin. Under the Swingle system, unshius are considered to be a group of mandarin varieties. Genetic analysis has shown the Satsuma to be a mandarin-pomelo hybrid.
Its fruit is "one of the sweetest citrus varieties, with a meltingly tender texture" and usually seedless, about the size of other mandarin oranges (Citrus reticulata). One of the distinguishing features of the satsuma is the thin, leathery skin dotted with large and prominent oil glands, which is lightly attached around the fruit, enabling it to be peeled very easily in comparison to other citrus fruits. The satsuma also has particularly delicate flesh.
Satsumas grown in humid areas may be ripe while the skin is still green. Satsumas are cold-hardy, and when planted in colder locations, the fruit becomes sweeter from the colder temperatures. A mature satsuma tree can survive down to −9 °C (15 °F) for a few hours.[Of the edible citrus varieties, only the kumquat is more cold-hardy. Satsumas rarely have any thorns.