(genus Thlaspi), plant of the mustard family (Brassicaceae), named and sometimes grown for its round seedpods. Most of the 60 species are Eurasian, but a few are native to North and South America, mostly in mountain areas. Common pennycress, or field pennycress (T. arvense), has penny-shaped (flattened and circular) notched pods, which are borne on stalks along the spike; at the ends of the spikes are small, white, four-petaled flowers.