Rosemary, an evergreen shrub, has been cultivated in Britain for its aromatic, faintly camphorous, needle-like leaves since the fourteenth century. Rosemary belongs to a small genus whose native distribution is the fire-prone Mediterranean region of Europe. Rosemary is widely used in Mediterranean cooking and is an important perfumery ingredient, for example, in eau de cologne and Hungary water. The plant's common and scientific names both derive from its classical Roman name ros marinus ('dew of the sea'), which apparently refers to its habitat close to the sea.
Across its natural range, rosemary shows great morphological variation. Its habit varies from prostrate, ground-covering forms through squat shrubs to tall fastigiated forms. The insect-pollinated flowers also vary in colour, from white through pink to blue and deep purple. Similarly, leaves vary in shape, size, colour and even chemistry, often giving the crushed leaves subtly different flavours and scents.
Rosemary leaves are long and thin, rigid and rolled over at the margins. They also have a thick cuticle on their dark upper surface and a dense carpet of simple and glandular hairs on their pale lower surface. Together such features are associated with a syndrome known as sclerophylly (literally 'hard leaf'), which is commonly found in Mediterranean plants. Various ideas have been proposed to explain sclerophylly in the Mediterranean flora, including adaptations to prolonged summer drought, herbivory and low soil nutrients.
In addition to drought, Mediterranean plants must also cope with fire; they do this using two broad strategies. One strategy is to resprout from buds, protected from fire, under the soil surface. The other strategy, which is adopted by rosemary, is to produce abundant seed so that when the adult plant is killed the plant population rapidly regenerates from the soil seed bank.
An adaptable, morphologically variable, easily managed, aromatic shrub makes an ideal garden plant. In the mid seventeenth century, rosemary was a functional plant, grown for its classical associations and its perceived medicinal and culinary value; occasionally it was used for hedging and topiary. In Oxford, the first Keepers (Jacob Bobart, father and son) of the Botanic Garden grew variegated and non-variegated types, whilst, in London, John Gerard and John Parkinson grew a handful of types in their gardens. In contrast, today, much of rosemary's natural variation is in cultivation, and a resurgence of interest has been shown because of rosemary's ability to grow in circumstances where water is limited.
Mateu-Andrés I et al. 2013. Geographical patterns of genetic variation in rosemary (Rosmarinus officinalis) in the Mediterranean basin. Botanical Journal of the Linnean Society 171: 700-712.