This winter-annual is a variable species (2n = 14, 28, 42) that has become increasingly common in east-central states during recent decades. It occurs mostly in a relatively narrow zone from Md. and Va. to s. Mo. and e. Kans. (K). In Ky. M. perfoliatum was first recorded in the 1930s (B) and it has now become a widespread weed, especially along dry gravelly roadsides. The genus Noccaea (= Microthlaspi of FNA 7) differs from Thlaspi in its seeds: yellowish-brown to brown, usuallly smooth (versus blackish-brown, striate of alveolate). Also, its leaves are usually less toothed and more glaucous (versus slightly glaucous to yellowish-green), and plants lacks the frequent fetid or garlic-like odor of Thlaspi. Compared to T. arvense, N. perfoliatum has much smaller mature fruits (mostly 3-6 x 3-6 mm versus 9-20 x 7-20 mm). with a shallower (up to 1.5 mm versus 5 mm), broadening (versus pinched) notch. Cauline leaves are ovate-cordate to suboblong (versus oblong). Mature plants are usually shorter (mostly 5-28 cm versus 15-55 cm), and not generally successful in cropland or pasture (Baskin & Baskin 1979).