Tumble-mustards are annual or biennial herbs in our area, usually somewhat stiff-hairy. The leaves are stalked to stalkless, pinnatifid to deeply lobed with backward or spreading segments, sometimes with the end segment the largest.
The flowers are arranged in clusters without bracts at bases. The 4 sepals are usually somewhat spreading, only slightly, if at all pouch-shaped at the base. The 4 petals are yellow, having the lower part narrowed to a so called claw. There are 6 stamens. The fruit pods are cylindrical, opening when ripe, mostly linear and narrow, straight to slightly curved, the valves with a prominent midnerve and also usually with 2 fairly prominent side. Style is almost or quite lacking, the stigma evidently 2-lobed. The seeds are arranged in 2 rows in our species, slightly if at all slimy when wet.
The genus has about 75 species, chiefly of the temperate zones of S. America and the Old World, ours are mostly introduced weeds. The name is a Latinized form of the Greek name for some member of the mustard family, possibly the water cress.