Whoever has examined the flower of the little yellow mustard knows that its four petals spread open like a cross. It has four sepals, also, each one lying between two petals. Curiously, there are six stamens, suggesting the Lily Family, but two of the stamens are short, only four appearing as if maintaining the flower number. The pod of this Family is different from that of any other, being 2-celled, with a partition down the middle. In opening for the escape of seeds, the outer sides split off from the middle and separate from the central portion. The pod may be long and narrow, or short and thick.

The flowers bloom in spikes, the lower ones being the oldest and often maturing into pods, while the tip of the spike is in bud. The colors are yellow, white, and purplish. Shepherd's purse, cress, black and white mustard belong here.