Pennycresses are annual or perennial herbs, hairless with simple, entire to toothed or lobed leaves, the stem leaves are alternate, with backward, ear-like lobes at the base.
The flowers are arranged in often extended clusters without bracts at bases. The 4 sepals are erect, not pouch-shaped at the base. The 4 petals are white in our species, and the flowers have 6 stamens. The fruit pods are much flattened, broad, often wing-edged, oblong-elliptic to obovate or obcordate in outline, pointed to rounded and notched, readily opening when ripe. The style varies from obsolete to slender and conspicuous. There are 2 to several seeds per cell, arranged in 1 row, not edged, very indistinctly to prominently lined or wrinkled concentrically in our species, not slimy when wet.
The genus has about 50 species, mostly of Eurasia. The name comes from an ancient Greek name for some plant of the family, believed to derive from thlaein, to crush, in reference to the flattened fruits.