Umeboshi

Umeboshi are pickled ume fruits. Ume is a species of fruit-bearing tree in the genus Prunus, which is often called a plum but is actually more closely related to the apricot. Umeboshi are a type of tsukemono, or traditional Japanese pickled food, and are very popular in Japan. Many Japanese have Umeboshi for breakfast or lunch.
http://en.wikipedia.org/wiki/Umeboshi

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