[Ledasmom]

Do you mean the wild mustard with yellow flowers, one to three feet tall, largish (up to six inch) leaves? There's a couple of other plants that may go by that name as well - if you have a description and location, that would be good. One of the plants called wild mustard is Synapis arvensis, also called Brassica arvensis or Brassica caber, but there seem to be others, mostly related to the plants used to produce cultivated mustard greens.