Erect glabrous annual or perennial herbs, with entire or dentate leaves, the basal ones forming a rosette, those of the stem, or at least the upper ones, auriculate and clasping. Flowers white or purplish. Siliques obcuneate, obcordate, or oblong-orbicular, mostly emar-ginate, flattened at right angles to the narrow septum, crested or winged. Valves dehiscent. Seeds 2 or several in each cell, wingless. Cotyledons accumbent. [Greek, to flatten, from the flat pod.]

A genus of about 25 species, natives of temperate, arctic and alpine regions. In addition to the following, 2 others occur in arctic America, the Rocky Mountains and California. Type species: Thlaspi arvense L.

Lower stem-leaves not clasping; seeds rugose.

1.

T. arvense.

All the stem-leaves cordate-clasping; seeds smooth.

2.

T. perfoliatum.

19 Thl spi Tourn L Sp Pl 645 1753 387