Citrus unshiu

Citrus unshiu is a semi-seedless and easy-peeling citrus species, also known as the satsuma mandarin or Japanese mandarin.

The unshiu is known as wēnzhōu mìgān (simplified Chinese: 温州蜜柑; traditional Chinese: 溫州蜜柑) in China, and mikan in Japan (or formally unshū mikan (温州蜜柑), the Japanese reading of the characters used in Chinese). In both languages, the name means "honey citrus of Wenzhou" (a city in Zhejiang province, China). An alternative Chinese name, wúhé jú (simplified Chinese: 无核橘; traditional Chinese: 無核橘), means "seedless mandarin".

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.

The Afrikaans name naartjie is also used in South African English. It came originally from the Tamil word nartei, meaning citrus.

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 highly inbred mandarin-pomelo hybrid, with 22% of its genome, a larger proportion than seen in most mandarins, coming from pomelo. It arose when a mandarin of the low-pomelo Huanglingmiao or kishumikan variety (placed in C. reticulata by Tanaka) was crossed with a pomelo or pomelo hybrid, then the resulting cultivar was backcrossed with another Huanglingmiao or kishumikan mandarin.

Citrus unshiu is one of the sweetest citrus varieties. It is usually seedless, and is about the size of other mandarin oranges (Citrus reticulata). Satsumas are known for their loose, leathery skin; the fruit is very easily peeled in comparison to other citrus fruits. The rind is often smooth to slightly rough with the shape of a medium to small flattened sphere. Satsumas usually have 10 to 12 easily separable segments with tough membranes. The flesh is particularly delicate, and cannot withstand the effects of careless handling. Coloring of the fruit is often dependent on climate; satsumas grown in humid areas may be ripe while the skin is still green while those grown in areas with cool night temperatures may see a brilliant reddish orange skin at peak.

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) or even −11 °C (12 °F) for a few hours. Of the edible citrus varieties, only the kumquat is more cold-hardy. Satsumas rarely have any thorns, an attribute that also makes them popular. They can be grown from seed, which takes about eight years until the first fruits are produced, or grafted onto other citrus rootstocks, such as trifoliate orange.

Various cultivars have been developed based on the Citrus unshiu, and in Japan, three cultivars, namely miyagawa wase, okitsu wase, and aoshima unshu, account for nearly half of the production volume of Citrus unshiu.