HOREHOUND (O. Eng. harhune, Ger. Andorn, Fr. marrube). Common or white horehound, Marrubium vulgare, of the natural order Labiatae, is a perennial herb with a short stout rootstock, and thick stems, about i ft. in height, which, as well as their numerous branches, are coated with a white or hoary felt whence the popular name of the plant. The leaves have long petioles, and are roundish or rhombic-ovate, with a bluntly toothed margin, much wrinkled, white and woolly below and pale green and downy above; the flowers are sessile, in dense whorls or clusters, small and dull-white, with a lo-toothed calyx and the upper lobe of the corolla long and bifid. The plant occurs in Europe, North Africa and West Asia to North-West India, and has been naturalized in parts of America. In Britain, where it is found generally on sandy or dry chalky ground, it is far from common. White horehound contains a volatile oil, resin, a crystallizable bitter principle termed marrubiin and other substances, and has a net unpleasant aromatic odour, and a persistent bitter taste. Formerly it was official in British pharmacopoeias; and the infusion, syrup or confection of horehound has long been in popular repute for the treatment of a host of dissimilar affections. Black horehound, Ballota nigra, is a hairy perennial herb, belonging to the same order, of foetid odour, is 2 to 3 ft. in height, and has stalked, roundishovate, toothed leaves and numerous flowers, in dense axillary clusters, with a green or purplish calyx, and a pale red-purple corolla. It occurs in Europe, North Africa and West Asia, and in Britain south of the Forth and Clyde, and has been introduced into North America.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)