This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
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.
All the stem-leaves cordate-clasping; seeds smooth.