This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Annual or perennial hairy decumbent herbs with axillary or terminal bracteate whorls. Calyx tubular-campanulate, 5-toothed. Corolla-tube naked, or with a ring of hairs within the dilated throat; upper lip deeply concave, lower 3-lobed. Stamens 4; anthers cohering in pairs, cells divergent. Nutlets triquetrous. There are between thirty and forty species, in temperate Europe, Asia, and North Africa. The generic name is a modification of throat, the form of the corolla. There are several indigenous species. The commonest, L. album, is a perennial with large white villous flowers produced from early Spring till Autumn. L. Galeobdolon, Yellow Archangel, is a handsome herb, plentiful in the South of England. It is hispid and glabrescent, with Nettle-like leaves and axillary whorls of showy yellow flowers spotted with reddish brown, appearing in May and June. L. pur-pwreum is an exceedingly common annual weed on cultivated grounds. L. maculdtum is very near L. album, with smaller foliage spotted or banded with white, and purplish flowers. This is the only one commonly seen in gardens, and it is occasionally found in waste places as a straggler from cultivation.
Leonurus Cardiaca, Motherwort, is a perennial herb from 2 to 3 feet high with deeply-lobed leaves and crowded whorls of purplish flowers having sharply-toothed calyces. Formerly cultivated, and now occasionally found in waste and neglected places.