WILD RADISH (Raphanus raphanistrum)

Often mistaken for Black Mustard. A check on the leaves, color of flower (pale yellow to white), color of stem, leaf veins, and prickly hairs will separate it from Black Mustard.

Basal rosette, leaves highly lobed, covered with stiff hairs, seed pods break into fragments. Wild Mustard (Brassica kaber) and Yellow Rocket (Barbarea vulgaris) leaves aren't as divided, lack stiff hairs, and their seed pods open straight down the middle

http://oak.ppws.vt.edu/scott/weed_id/rapra.htm