Japanese citrus fruits were first mentioned in theKojiki andNihonshoki, compiled in the 700s, and theMan'yōshū andKokin Wakashū, poetry anthologies compiled in the 700s and 900s, mention theTachibana orange as a subject ofwaka poetry and describe its use as a medicinal, ornamental, and incense plant.
Throughout their history, the Japanese have created and cultivated various varieties of citrus fruits, taking advantage of the mild climate that is ideal for growing citrus. In particular, from the 1600s during theEdo period (1603–1868) to the present, various varieties of citrus fruits have been produced, includingUnshū,Natsumikan,Hassaku,Iyokan, andDekopon. At present, Unshū is the most widely grown in Japan, and variouscultivars have been developed.
At present, the largest citrus growing areas are located in theprefectures ofWakayama,Shizuoka,Tokushima,Kochi,Oita,Miyazaki andEhime.
Citrus fruits are believed to have originated inAssam, India and the foothills of theHimalayas, and later spread throughout the world. In October 2023, published genetic research proved that the ancestor of the citrus plants originated in India more than 25 million years ago and evolved into the true citrus species in southern China 8 million years ago, followed by early citrus species such as pomelo and citron that originated in the foothills of the Himalayas.[1]Yuzu, kunembo, anddaidai, are believed to have been introduced to Japan from China between the Nara (710–794) and Muromachi periods (1336–1573).[2]
TheKojiki andNihon Shoki, compiled in the 700s, were the first books inJapan to describe citrus fruits. TheNihon Shoki states that a man namedTajimamori brought back citrus fruits from theTokoyo no kuni (Land of immortality,ja:常世の国) on the orders ofEmperor Suinin, which is thought to refer to thetachibana orange that grows wild in Japan. TheMan'yōshū, a collection of poems from the same period, contains many poems about tachibana orange, and because of its strong acidity at the time, it was dried and used for medicinal and ornamental purposes rather than for food. TheKokin Wakashū, compiled in the 900s, mentions that tachibana orange was burned and used as incense to give a nice fragrance tokimonos. In Japan, tachibana orange is a symbol of eternity and is the motif for theOrder of Culture.[3][4]
The most widely grown variety in Japan today is theunshu mikan (Citrus unshiu), also known as the satsuma orange. There are two theories about the origin of the unshu mikan. One is that unshu mikan originated in Japan, while the other is that it originated in China. According to the Japanese origin theory, several species that would serve as the parents of unshu mikan were introduced from China, and in the 1600s, they were born in Nishi-Nakajima,Higo Province (laterNagashima, Kagoshima) in Japan.The Japanese Ministry of Agriculture, Forestry and Fisheries,Ehime Prefecture and Japanese scientists support this theory of Japanese origin.[5][6][7][8][9] Genetic research has shown that the unshu mikan is a cross between the kishu and kunembo.[10][11] During the Edo period, unshu mikan were not very popular due to a superstition that eating seedless unshu mikan would make one infertile. It was not until theMeiji era (1868–1912), when modernization began, that the popularity of unshu mikan increased.[9] From the mid-Edo period (1603–1867) to the mid-Meiji era (1868–1912), kishu mikan were the mainstay of cultivation.[2]
From the Edo period (1603–1867) to the present, the Japanese have created numerous varieties of citrus fruits, collectively known astyūbankan (中晩柑). It is a general term for citrus fruits shipped from January to May, after the shipping period of unshu mikan, which is from October to February.[2][12][13] For example,natsumikan (Citrus natsudaidai) was developed around 1700,[14]hassaku in 1860,[15]andiyokan in 1886.[16]Kiyomi,Setoka andKanpei are also types oftyūbankan.[12][13]dekopon, created in 1972, is one of the most popular varieties internationally. Dekopon was introduced to South Korea in the 1990s and became popular as Hallabong, was exported to California in 1998, and has been marketed as "Sumo Citrus" since 2011.[17]
Japan's warm summer climate makes it particularly suitable for citrus plants; while they are grown all over the country, the largest citrus growing areas are located in theprefectures ofWakayama,Shizuoka,Tokushima,Kochi,Oita,Miyazaki andEhime.[18] In Japan, variouscultivars have been developed based on the unshu mikan, and three cultivars, namely miyagawa wase, okitsu wase, and aoshima unshu, account for nearly half of the production volume of unshu mikan.[19]
Japan usually follows thebotanical names of thetaxonomy fromTyôzaburô Tanaka, often referred to as the "Tanaka system", giving for each cultivar a separate name no matter if it is pure or ahybrid of two or more species or varieties. While elsewhere it is more popular to classify thegenuscitrus intospecies, and further intovarieties, and then into cultivars or hybrid. Such a system was created byWalter Tennyson Swingle fromFlorida and is called the "Swingle system".[20] The different approaches of the two systems lead to partially-overlapping or nested 'species', for example,Citrus unshiu andCitrus tangerina (Tanaka) versusCitrus reticulata (Swingle). Likewise, common terms, like "mikan", do not always align with these taxonomic groups.
Japanese citrus fruits include the following:[21]
| Common name(s) | Image | Taxonomic name/constituents | Notes |
|---|---|---|---|
| Amanatsu |  | Citrus ×natsudaidai | Yellowish-orange in colour, about the size ofgrapefruit andoblate in shape. The fruit contains 12 segments and about 30 seeds. |
| Banpeiyu (pomelo cultivar) |  | Citrus maxima | |
| Bushukan (Buddha's hand) |  | Citrus medica var.sarcodactylis | |
| Daidai |  | Citrus ×daidai | |
| Dekopon |  | Citrus unshiu ×sinensis ×C. poonensis | |
| Haruka |  | Citrus tamurana ×natsudaidai | |
| Hassaku |  | Citrus ×hassaku | |
| Hyuganatsu |  | Citrus tamurana | |
| Iyokan |  | Citrus ×iyo | |
| Jabara |  | Citrus ×jabara | |
| Kabosu |  | Citrus sphaerocarpa | |
| Karatachi (Japanese bitter orange) |  | Citrus trifoliata | |
| Kanpei |  | 'Dekopon' × 'nishinokaori' | |
| Kawachi Bankan (Mishokan) |  | Citrus kawachiensis | |
| Kinkan (Kumquat) |  | Citrus japonica | |
| Kinkoji unshiu | Citrus obovoidea ×unshiu | ||
| Kishu | .png) | Citrus kinokuni | |
| Kiyomi |  | Citrus unshiu ×sinensis | |
| Kobayashi mikan | Citrus natsudaidai ×unshiu | ||
| Koji orange |  | Citrus leiocarpa | |
| Mikan | | Citrus unshiu | |
| Ōgonkan |  | Citrus flaviculpus | |
| Ponkan (Tangerine) |  | Citrus poonensis | |
| Reikou | |||
| Sakurajima komikan (mandarin orange cultivar), |  | Citrus × sinensis | |
| Sanbokan |  | Citrus sulcata | |
| Shonan gold |  | Citrus flaviculpus ×Citrus unshiu | |
| Shikuwasa (Shiikwaasaa, Shequasar, Hirami lemon) |  | Citrus × depressa | |
| Sudachi |  | Citrus sudachi | |
| Tachibana |  | Citrus tachibana orCitrus reticulata var.tachibana | |
| Tankan | Citrus poonensis ×Citrus sinensis | ||
| Tsunonozomi | 'Kiyomi' × 'Encore' | ||
| Yukou |  | Citrus yuko | |
| Yuzu | .jpg) | Citrus junos |
Therefore, it is likely that kunenbo was backcrossed to Kishu in the Kagoshima region of Japan several times and Satsuma and Yatsushiro were selected from their offspring.
(After the many years of research,Dr. Tanaka has concluded the place of origin of Satsuma isNagashima, Kagoshima. Satsuma is achance seedling of Sōkitsu, Mankitsu, or Tendaisankitsu introduced from Huangyan Zhejiang, China. It appeared in the early Edo period. The place where Satsuma was born by mutation was Nishi-nakajima, Amakusa District, Higo Province (later Nagashima, Kagoshima), and was called Nakajima Mikan or Nagashima Mikan.)
During the Edo period, when Kishu mikan were being cultivated, unshu mikan were already being cultivated. However, they were not yet called unshu mikan, but Nakajima mikan. Although mandarins were a luxury, unshu mikan were not the most popular. The unshu mikan is unique in that it is ready to peel and has no seeds. The lack of seeds is good because they are easy to eat, but in the Edo period, the lack of seeds was a factor that made them unpopular. It was believed that eating seedless fruit meant that one could no longer produce offspring, thus ending one's family lineage. When the fruit was named "unshu mikan" in the late Edo period, it was finally recognized. Wenzhou is a mandarin production area in China, and the name "unshu mikan" means "a mandarin comparable to the one produced in Wenzhou". The unshu mikan is often mistaken for a mandarin imported from China, but it is a genuine Japanese mandarin. It was not until the Meiji period that the cultivation of unshu mikan became popular.
