Mustard seeds, both white and brown, are nearly globular in shape, finely pitted, odourless when whole, and pungent-tasting. White mustard seeds are light yellow in colour and about 2.5 mm (0.1 inch) in diameter. Brown mustard seeds are about the same size but are a darker yellow in colour. Mustard greens have broad, wavy frilled leaves with longitudinal veins and a deep green color. The upright leaves are supported by coarse stems that can be quite fibrous when fully mature. Smaller leaves are considerably tenderer, while larger Mustard greens may require cooking.