Laurus nobilis L. (Lauraceae)



Laurus nobilis in Oxford Botanic Garden (February 2014). Laurus nobilis watercolour painted by Ferdinand Bauer (late 1780s/early 1790s) for the Flora Graeca (Sherardian Library; MS Sherard 245.f24r). Laurus nobilis in Oxford Botanic Garden (April 2014).

Bay is an insect-pollinated, bird-dispersed, evergreen tree which is a relic of the laurel forests that covered southern Europe and northern Africa 20-60 million years ago. Today, such laurel forests are restricted to Macaronesia, whilst the natural distribution of bay is confined to pockets of Morocco, Macaronesia, the southern Black Sea and Mediterranean Basin. However, bay has been cultivated for millennia as an ornamental and for its aromatic leaves and classical symbolism, something Linnaeus maintained when he named the species nobilis (noble).

References to laurel, whether literary or visual, are frequent in classical art, and laurel wreaths festoon Europeans commemorated during the eighteenth and nineteenth centuries. Bay is also an iconic element of Mediterranean cuisine, which has been exported globally as Mediterranean culture and peoples travelled.

There is natural variation among bay populations and some minute morphological differences have been used to define additional Laurus species. Consequently, depending on your taxonomy, one or two additional Laurus species have been identified and are confined to Macaronesia. Macaronesian plant diversity has captivated people since the sixteenth century, whilst biologists have been fascinated by how plants have evolved on islands since Darwin.

Morphology, anatomy and ecology can be important sources of data, especially when combined with genetic data from DNA. DNA can be used to investigate ancient relationships and evolutionary events since mutations are passed between generations and footprints of change may be retained for thousands, if not millions, of years. Combining such data with information about fossil distributions and mathematical models of past areas suitable for a species survival, areas can be identified where organisms might have been concentrated and routes by which the colonised or decolonised areas as climatic conditions changed.

Using such an approach, and sampling wild bay trees from across the species' range, three distinct genetic groups, primarily related to geography, have been discovered. An eastern group of bay trees is found in Turkey and the Near East. A western group is found in Macaronesia and the central and western Mediterranean, whilst a third group is found in the Aegean region. Superimposed onto this general outline is a more complex pattern of repeated dynamic change in bay tree distribution and population size. The overall similarity of bay tree DNA from across its range and the close relationship among populations sampled in Macaronesia and Morocco implies that bay ought to be treated as a single species across its entire range.

Further reading

Rodríguez-Sánchez F et al. 2009. Late Neogene history of the laurel tree (Laurus L., Lauraceae) based on phylogeographical analyses of Mediterranean and Macaronesian populations. Journal of Biogeography 36, 1270-1281.

Stephen Harris