As a rule of thumb, the region of natural olive growth defines the European Mediterranean region. Olives are evergreen, medium-sized trees, with often characteristically gnarled, twisted, squat trunks. The elliptical leaves, arranged opposite each other along the young stems are covered in tiny hairs, mushroom-like under magnification, that give them a characteristic silvery-green appearance. The tiny, white flowers form in elongated clusters in the leaf axils and eventually produce small, oil-rich, plum-like fruits; olives are harvested when they are green or purple. While wild olives generally reproduce sexually by seed, domesticated olives usually reproduce clonally. Domesticated olives raised from seed usually produce poor-quality fruit.
The olive is one of the world's oldest cultivated plants. Olives have been an economic backbone and article of international commerce for peoples around the Mediterranean, stretching into western Iran, for at least 7,000 years. Cultivated olive trees grow through much of Iberia and in a fringe along the northern and eastern coasts of the Mediterranean Sea. By the end of the end of sixteenth century, olives had been established in the New World, especially in those regions with warm, wet winters and hot, dry summers, such as California and central Chile. Over the past century, with the increased global demand for olive products, cultivation has extended to all the world's Mediterranean regions, including parts of South Africa and New Zealand.
The cultivated olive is a part of a large, variable complex of wild olives. The details of olive domestication and its close wild relatives are poorly known but the available evidence suggests olives were first brought into cultivation in the Levant. Since they were first domesticated, olives have escaped back into the wild, confusing boundaries, while the ebb and flow of olive genes among wild, feral and cultivated trees has created enormous diversity, the tangle further complicated by thousands of recorded olive cultivars.
In the late-1780s, John Sibthorp, Professor of Botany in Oxford University and recently returned from his pioneering explorations of the eastern Mediterranean, discussed the olive with his students. However, Oxford Botanic Garden's glasshouses were so poor he had to resort to showing the students a painting recently completed by the artist Ferdinand Bauer, who had accompanied him on his explorations: 'our Olive Tree tho' it produces its flowers, seldom ripens its Fruits & that you may have a more perfect Idea of it I shall show You the fructification in a drawing'.
Breton C et al. 2006. Genetic diversity and gene flow between the wild olive (oleaster, Olea europaea L.) and the olive: several Plio-Pleistocene refuge zones in the Mediterranean Basin suggested by simple sequence repeats analysis. Journal of Biogeography 33: 1916-1928.
Lumaret R and Ouazzani N 2001. Ancient wild olives in Mediterranean forests. Nature 413: 700.
Zohary D 1995. Olive, Olea europaea (Oleaceae). In: J Smartt & NW Simmonds, Evolution of crop plants. Longman, London, pp. 379-382.
The 25th July 2021 marks 400 years of botanical research and teaching by the University of Oxford.
As a celebration and count-down to this anniversary, the University of Oxford Botanic Garden and Harcourt Arboretum, together with the Oxford University Herbaria and the Department of Plant Sciences, will highlight 400 plants of scientific and cultural significance. One plant will be profiled weekly, and illustrated with images from Oxford University's living and preserved collections.
Follow us on Twitter @Plants400
The data and images available on this site may only be used for scientific purposes. They may not be sold or used for commercial purposes. All images are copyright of the University of Oxford, unless otherwise indicated.
The specimens at the Oxford herbaria and the living collections of the Oxford Botanic Garden and Oxford University Herbaria are being digitized using BRAHMS.
Dr Stephen Harris (email@example.com)