Marrubium

Marrubium is a genus of flowering plants in the mint family (Lamiaceae), commonly known as horehounds. It comprises about 20 species native to Europe, North Africa, and western Asia, with Marrubium vulgare (common horehound) being the most widely known and used.

Description: Marrubium species are herbaceous perennials with square stems and opposite, densely hairy leaves that are often wrinkled and grey-green. The leaves are typically oblong to ovate with crenate margins. Inflorescences are dense clusters of small flowers, usually white to pale lilac, arranged in verticillasters at the ends of the stems. The overall habit is compact to spreading, and many species carry a characteristic camphor-like scent when crushed.

Distribution and habitat: The genus is native to the Mediterranean region and surrounding areas, extending into parts of Europe, North Africa, and western Asia. It has been naturalized in many other temperate regions. Marrubium plants prefer sunny, well-drained sites and are commonly found in dry, rocky soils, grasslands, roadsides, and hedgerows.

Chemistry and uses: Marrubium contains bitter compounds and diterpenoids, including marrubiin, as well as various essential oils. Traditionally, species such as M. vulgare have been used as an herbal remedy for coughs and respiratory issues, and the foliage or extracts are used to flavor candies and beverages in some cultures (notably in horehound candy). Modern evidence for medicinal efficacy is limited, and use should be approached with caution and professional advice where appropriate.

Cultivation and taxonomy: Numerous species are recognized within the genus, with Marrubium vulgare being the most widely cultivated and studied. They are generally easy to grow, preferring full sun and well-drained soil; some species can spread or naturalize if conditions are favorable.