Cultivated in Japan since the Stone Age, yamaimo provides high levels of vitamin C and B1. Varieties of yamaimo include nagaimo (Chinese yam), ichoimo (ginkgo yam, so called because the end of the plant spreads out like a ginkgo leaf) and round yamatoimo (Japanese yam). Yamaimo is often grated to make tororo paste, which can be placed on wheat rice to make mugitoro gohan, diced tuna sashimi to make yamakake and soba noodles for yamakake soba.