Mustard is a herbaceous plant - i.e. which flowers once a year and does not form wood nor cork around its stems - in which botanists distinguish about forty species of mustard seeds. A dozen of them grow naturally in Europe, like the very prolific field mustard (or wild mustard) or white mustard that is used as fodder for dairy cows. Others were introduced there, such as brown mustard or Chinese mustard, which was definitely brought into cultivation around the beginning of the 20th century. This hybrid species, vigorous and of excellent flavor, constitutes the main ingredient of Dijon mustard.