Marrubium is a genus of flowering herbaceous plants in the mint family. Otherwise known as horehound, members of this genus are found throughout temperate climate zones in Asia and Europe, with around 40 known representative species. Several species are grown ornamentally and one, M. vulgare, has been used historically as a medicinal plant and a source of flavoring for candy. Nurseries sometimes carry Marrubium for gardeners interested in cultivating this plant ornamentally or for the production of herbal preparations.
Like other members of the mint family, Marrubium has distinctively square stems. The plant tends to grow low to the ground, with an upright growth habit. The leaves, often slightly crinkled and toothed, are covered with fine hair. Small white to purple flowers are produced at the tips of the stems in the summer and fall. When crushed, Marrubium releases a distinctive crisp, minty scent. The plant spreads quickly in conditions where it is happy, and can become a large massed planting in a short period of time.
Herbal uses of this plant date back thousands of years, with evidence that a number of ancient cultures used it in the treatment of coughs, colds, intestinal discomfort, and pain. Horehound lozenges and drops continue to be used in many regions to treat coughs and sore throats, although studies on the use of the plant show it may be of questionable efficiency. Hard candies made with this plant are available in some places, along with products like tisanes.
Members of this genus thrive in a variety of conditions and are very easy to grow. In the wild, Marrubium is often found in locations like ditches and other areas with soil of dubious quality. In the garden, this plant can be established almost anywhere. Water requirements are not high and the main concern is overrunning the garden. If the plant is not controlled, it can sprawl very quickly. Since it grows faster than many other plants, it can overwhelm neighboring plants in the garden.
In some areas where Marrubium has been introduced, it has become an invasive species. M. vulgare is a particularly problematic invasive plant in some areas of the world because it has been carried far and wide by people growing it for medicinal purposes. As people give up on medicinal gardens or fail to care for them attentively, the plants escape into the wild and may threaten delicate native species by competing for resources and choking out slower-growing plants.