Source, Etc

White horehound, Marrubium vulgare, Linne (N.O. Labiatoe), is an erect herbaceous plant with perennial root, widely distributed over Europe, but not very common in England. It is, however, cultivated as well as collected wild in various parts of the country for medicinal use, and is also imported from the south of France. The Romans esteemed horehound as one of the most valuable drugs, but at present it is used only as a domestic remedy and that not to any great extent. The plant is cut when in flower, and dried.

Description

White horehound grows to a height of about 50 cm., and possesses a quadrangular, branching stem densely clothed with white woolly hairs. The leaves are from 3 to 5 cm. long, opposite and petiolate; the lower rounded-ovate, the upper ovate-acuminate, with dentate or dentate-crenate margin. They are much wrinkled, and both the upper and under surfaces, but especially the latter, are covered with white felted hairs.

The flowers are arranged in dense verticillasters in the axils of the upper leaves. The hairy calyx is provided with ten recurved, hooked teeth; the whitish bilabiate corolla is characterised by its small, erect, cleft upper lip.

The drug has an agreeable though not powerful odour, and a somewhat aromatic but very bitter taste.

The student should observe

(a) The dense felted hairs on the stem and leaves,

(b) The ten hooked teeth of the calyx.

Constituents

White horehound contains a bitter principle, mar-rubiin (0.25 per cent.), crystallising in colourless plates melting at 154°; it is almost insoluble in water, but soluble in alcohol and ether; a little volatile oil and tannin are also present.

Uses

Horehound has tonic, stimulant, and expectorant properties; it is used as a domestic remedy for coughs and pulmonary complaints generally.

Substitutes

The following plants have been substituted for M. vulgare: -

M. peregrinum, Linne; has ten straight calyx teeth.

M. candidissimum, Linne, has five nearly straight calyx teeth; is less aromatic and less bitter.

Ballota nigra, Linne (black horehound); is dark green; hairs rough, not woolly; five broadly ovate, pointed calyx teeth.

B. hirsuta, Bentham; calyx funnel-shaped, densely hairy, with ten broadly acute or mucronate teeth,