M. officinalis: annual or biennial; steins erect, 2-4 feet high, branched, glabrous; leaves distant, on long leafstalks; the leaflets obovate or nearly orbicular, those of the upper leaves narrower, often linear; flowers numerous, bright yellow, in long, axillary racemes; pod oval. - Roadsides, banks, and bushy places. Fl. June to August.
M. arvensis has the leaflets rather broader, and the racemes looser, with fewer flowers; probably introduced.
M. alba has harder and more wiry stems, narrower leaflets, and white flowers, and is also occasionally found, but probably introduced with corn or ballast.