pennycress 
noun
A European weed with flat round pods, which has become naturalized in North America.
- Thlaspi arvense, family Cruciferae.
- The worst weeds in winter wheat are those that germinate in the fall with the crop - downy brome, jointed goatgrass, volunteer rye, blue mustard, tansy mustard, field pennycress, wild mustard, and shepherd's purse.
- Weeds like pennycress, downy brome, mustards, cheatgrass, and shepherd's purse are common in first cut alfalfa.