Plant 306

Thymus species (Lamiaceae)


Thymus, one of the largest genera in the mint family, is distributed throughout the arid, temperate and cold regions of Eurasia and North Africa, to as far west as southern Greenland. The genus is particularly speciose around the Mediterranean Sea, where it has been used by ancient cultures for thousands of years. The Egyptians used it in perfumery, cosmetics and embalming. The Greeks and Romans used it as a medicine and fumigant for its antiseptic properties. Symbolically, Thymus species have been associated with courage, grace and even republicanism. However, thyme is best known as a flavouring agent for all manner of European, North African and western Asian cuisines.

The distinctive odour of Thymus is due to the presence of thymol, an aromatic phenolic compound with strong antimicrobial properties. Today, oil of thymol is an active ingredient in products as diverse as food preservatives, ringworm powders, toothpastes, mouth washes and pesticides. The value of commercial thymol contributes to Thymus being one of the most economically important members of the mint family.

The antiseptic properties of thymol were independently recognised in cultures outside of western Europe. Native Americans used species of Monarda, also in the mint family, for their aromatic and antiseptic properties. Similarly, the tiny fruits of the Indian spice ajowan (Trachyspermum ammi), a member of the carrot family, have been used for thousands of years in Ayurvedic medicine. Indeed, by the early twentieth century, over 1,000 tonnes of ajowan fruits were imported annually into Europe from India for the commercial extraction of oil of thymol.

There are native Thymus species in Britain, although the cultivation of thyme was probably introduced by the Romans. Today, many different Thymus species, and cultivars selected from the variation within species, are grown in gardens because of the diversity of their odours, form and colour. They are also valuable nectar sources for bees.

Features that make Thymus species attractive to gardeners also make them difficult to identify. As climates have changed over the last 50,000 years the natural distributions of Thymus species have shifted. This produced complex patterns of morphological and genetic variation as species adapted to new conditions, hybridisation between previously isolated species occurred and hybrids became established.

In their native European ranges, some Thymus species are associated with close-cropped, well-drained grassland. Such habitats, which support many plant and animal species, are recognised as important for conservation and have high conservation priority in Europe.

Further reading

Broeck AV et al. 2015. Dispersal constraints for the conservation of the grassland herb Thymus pulegioides L. in a highly fragmented agricultural landscape. Conservation Genetics 16: 765-776.

Federici S et al. 2013. DNA barcoding to analyse taxonomically complex groups in plants: the case of Thymus (Lamiaceae). Botanical Journal of the Linnean Society 171: 687-699.

Stephen Harris