An Illustrated Guide to ARIZONA WEEDS
The University of Arizona Press
HOREHOUND-Marrubium vulgare L.
DESCRIPTION-An upright bushy perennial which reproduces only by seeds. It has dense white woolly 4-angled stems branching from the base, 3/4 to 2 1/2 feet high. Both the stout stems and the leaves have a bitter taste. The opposite leaves are round, corrugated, and 1 to 2 inches long including the stalks. They are green above, and white woolly beneath, with rounded teeth along the margins.
The small white tubular flowers, 1/4 to 1/3 inch long, are crowded into dense clusters around the stem at the base of the leaf stalks. The flowers are stalkless, and the clusters are very dense and compact around the stem. These flower groups occur at the ends of all the branches, and often extend for more than a foot on the stem. The calyx is also tubular, with 10 spinelike teeth which curve downward and are hooktipped in age. The calyx is persistent, and encloses the 4-parted fruits.
At maturity the fruit separates into 4 seedlike nutlets, which are 1-seeded and commonly referred to as seeds. They are eggshaped, brown or dark gray, about 1/12 inch long, and somewhat 3-angled; the surface has scattered dark granules.
DISTRIBUTION-Horehound is a widespread European perennial. It grows in dry soil and is a common weed of old fields, waste places, and roadsides, especially in the vicinity of permanent stock water, bedgrounds, and sheep or goat corrals. It extends throughout the state, and is abundant in many areas. It has a wide altitudinal variation, from 100 to 8,500 feet elevation; flowering May to October.
The hooked teeth of the calyx may become attached to wool or mohair, and thus lower its value. The tops of the plants are used medicinally for cough medicines, and for candy flavoring.
Copyright (c) 1972 The Arizona Board of Regents