Seed pod of the field pennycress, Thlaspi arvense. The dark seeds can be seen through the seed pod. Pennycress is considered an agricultural crop weed that grows on waste ground and headlands throughout Europe, USA, eastern Asia & northern Africa. It is also known as stinkweed due to its unpleasant smell. Stinkweed seeds live for up to six years in the tillage zone, and buried deeper they can live for 20 years and germinate when brought to the ground surface.