21-40 days to maturity. Brassica rapa var. japonica. Early Mibuna Mustard Seeds. Non-GMO, warm or cool-season, annual, heirloom. Similar to mizuna greens, mibuna mustard is a flavorful Japanese green strap leaf mustard with a mild mustard flavor. Although it is very similar to the mizuna plant, differentiate mibuna by its smooth, pointed leaves and distinct flavor. This traditional (heirloom) Japanese green vegetable, dento yasai, is cultivated in Mibu, Kyoto prefecture. An early open-pollinated variety, this vigorous grower produces a dense cluster of long, narrow, rounded, dark green leaves. Early Mibuna greens are a cold and heat-tolerant crop suitable for all gardens. Approx. 11,100 seeds / oz.