Natsudaidai, commonly known as the Japanese summer orange, is a large, late-ripening citrus variety traditionally grown in Japan and historically important as the foundation for several improved selections such as Kawano Natsudaidai and Nanshodaidai. Supposedly made up of pummelo and mandarin DNA. Believed to have originated from a seed that drifted ashore in Yamaguchi Prefecture (Japan) about 1870. It seems to be a hybrid of pummelo and another citrus. The fruit are large (400-500 g), have a thick skin and 30 seeds on average, taste very sour, and contain 2-3% acid.