Dekopon

 is a seedless and sweet variety of mandarin orange.
It is a hybrid between Kiyomi and ponkan (Nakano no.3), developed in Japan in 1972.
Originally a brand name, "Dekopon" has become a genericized trademark and it is used to refer to all brands of the fruit; the generic name is . Dekopon is distinctive due to its sweet taste, large size and the large protruding bump on the top of the fruit.
Names.
The name is most likely a portmanteau between the word "deko" (凸, デコ; meaning "convex") as a reference to its bump, and the "pon" in ponkan (ポンカン; one of the fruits that it is derived from) to create "dekopon" (デコポン).
There were many market names for dekopon during the time the name was a trademark of the product from Kumamoto. For instance, "himepon" was the market name for the fruits originating from Ehime prefecture. The ones grown in Hiroshima prefecture were marketed as "hiropon". After an agreement whereby anyone could use the name "dekopon" by paying a fee and meeting certain quality standards, the name was used for the fruit no matter where it came from in Japan.
'Dekopon' does not have an agricultural variety registration number ("Nōrin Bangō") because of its bump, which at the time of its development was considered to be unsightly, and failure to reduce acidity in the fruit.
Cultivation.
The fruits are usually grown in large greenhouses to keep them at a constant temperature, and are harvested from December to February (winter in Japan). In the case of garden farming, they are harvested from March to April. After harvesting, dekopon are usually left for a period of 20–40 days so that the levels of citric acid in the fruit decrease, while the sugar levels increase to make a more appealing taste to market. Only products with sugar level above 13°Bx and citric acid below 1.0% can be sold with the name dekopon.
Outside Japan.
In Brazil, dekopon is marketed under the brand name of "Kinsei" which derived from the Japanese word for Venus. Brazilian farmers have succeeded in adapting the variety to tropical to temperate climate in the highlands of São Paulo state. The work was done by Unkichi Taniwaki, a farmer of Japanese origin. "Kinsei" is easily harvested from May to September. In the high season for "kinsei", each fruit costs around 0.50 USD at the Brazilian street market and supermarkets.
In South Korea and Azerbaijan dekopon is called "hallabong" (한라봉) named after Hallasan, the mountain located in Jeju Island, where it is primarily grown.
The citrus budwood was imported into the United States in 1998 by a California citrus grower, Brad Stark Jr. The rights to the sterilized budwood were purchased in 2005 by the Griffith family, owners of the nursery TreeSource and packing facility Suntreat. The dekopon was released as a commercial product in the US under the name "Sumo Citrus(R)" in early 2011.
Others.
Dekopon have become so popular in Japan that the chewing candy brand giant Hi-Chew (ハイチュウ) has released a limited-edition dekopon flavor.
In commemoration of the 15th anniversary of the first shipment of dekopon, Japan Fruit Growers Cooperative Association designated 1 March "Dekopon day" in 2006.