M. annua: annual; stems erect, glabrous, 1/2-1 foot high, with opposite branches; leaves ovate or oblong, coarsely-toothed, of a thin texture; male flowers clustered along slender peduncles nearly as long as the leaves; females 2-3 together in the axils of the leaves, usually on separate plants. - Cultivated and waste places. Fl. August, September.