|Sumo tangerines at Family Market|
According to David Karp's LA Times article, they're a Japanese product originally called Dekopon and now grown in California through a consortium that actually grew them in secrecy starting in 2008. They're sold under the Sumo brand name.
According to me, they're delicious. The Sumo is a large, sweet fruit with lots of juice. The peel pulls away easily. The section have a skin so thin that it's almost like they're all pulp. You get a strong citrus flavor, less sweet than those tiny oranges and more flavor of great fresh-squeezed juice. The fruit have a distinctive bump at one end. They're cute enough to display, although they won't last long once you have tasted them.
Hat tip to the Keep It Up David blog where I found the link to the LA Times and David's recipe for a salad that uses the Sumo tangerines.
Check out Karp's article for more details and a better description. Then check out the fruit at Family Market (and maybe other Asian groceries?). Fruit that once cost $10 each in Japan now sells $8 for a nine-fruit box. Or they had packages of two in a refrigerated section for $1.50.