From the L.A. Times:
Think of a huge mandarin, easy to peel and seedless, with firm flesh that melts in the mouth, an intense sweetness balanced by refreshing acidity, and a complex, lingering mandarin orange aroma. I've tasted more than 1,000 varieties of citrus, and to me the Dekopon is the most delicious.
The Dekopon, which will be marketed here under the name Sumo, originated in 1972 at a government fruit research station in Nagasaki Prefecture, Japan, as a hybrid of Kiyomi tangor (a cross of orange and satsuma mandarin) and a ponkan, a large mandarin popular in Asia. Initially it seemed unpromising because of its homely appearance, with rough, yellow-orange skin and a distinctive bump at the top. But by the 1990s, as Japanese consumers came to appreciate its rich flavor, Dekopon became the country's most prized and expensive citrus, fetching as much as $10 apiece.