Assessing past agrobiodiversity of Prunus avium L. (Rosaceae): a morphometric approach focussed on the stones from the archaeological site Htel-Dieu (16th century, Tours, France)

Abundant and diverse Prunus fruitstone remains from cherries, plums, sloes, peaches, etc. are frequently recovered from archaeological waterlogged contexts such as wells, latrines, lake dwellings etc. in Europe. The distinction between most of the Prunus species, based on traditional morphological characters of the fruit stones, is usually not problematic. However the discrimination between P. avium L., P. cerasus L. and related cherry species, based on classical criteria alone, often turns out to be ambiguous because of the increasing number of varieties which have been bred since Roman times. By combining geometric and traditional morphometrical approaches, the overall variation in shape and size of stones from French and Swiss excavations dating from the 1st century to the 16th century a.d. were assessed. Among these important archaeobotanical data, the detailed examination of 100 waterlogged stones from the 16th century Htel-Dieu cesspit at Tours, France, revealed that the morphological diversity is structured into two distinct morphotypes which diverge mainly according to geometrical features. Finally, the comparison between morphological features of these well-preserved archaeological stones and modern reference material including P. avium, P. cerasus and P. x gondouinii, suggests that these two morphotypes, which have been initially attributed to P. avium (long stones) and P. avium/cerasus (rounded stones) according to traditional morphological parameters, would correspond to two different cultivated varieties, both belonging to Prunus avium. Results presented in this work constitute new and preliminary data obtained during the development of this project that throw light on morphological variability and biosystematic aspects.