Olive tree varieties cultivated for the great Baetican oil trade between the 1st and the 4th centuries AD: morphometric analysis of olive stones from Las Delicias (Ecija, Province of Seville, Spain)

During the excavations of a Roman amphora workshop and oil mill of the 1st–4th century AD in Las Delicias, Genil valley, Ecija, Spain, large quantities of charred olive stones were recovered. The assemblages discovered in the pottery kilns demonstrate the use as fuel of olive residues, which were obtained from the extraction of the oil in the nearby mill. The abundance of material offered the opportunity to study the infra-specific diversity of the olives growing in the province of Baetica, which is known to have been an important oil-producing region during the Roman Empire. In total, 335 intact charred archaeological olive stones were analysed using geometric morphometry (outline analysis) and compared with several current morphotypes. These have been identified within a set of dimensional references of the stones established from the morphometric study of current varieties and wild populations, including genuinely wild and feral forms of olives, from various areas around the Mediterranean. The morphotype mainly found in wild populations was widely represented among the olive stones from Las Delicias. A large proportion of the archaeological stones were however close to various domesticated forms, which reflect the history of the region and of its varied cultural Mediterranean influences, Punic, Greek and Roman. Moreover, intermediate forms between two distinct morphotypes were identified. They suggest that hybrid olive trees derived from crosses among domesticated varieties and also between domesticated and wild forms, were grown in Las Delicias. In the Genil valley, Roman olive cultivation was based on a set of local olives which included wild and domesticated varieties from various origins, and whose diversity arose from breeding for improvement of varieties.