Image Analysis application on waterlogged archaeological Prunus remains from a medieval context in Sardinia

Fruit remains such as cherries, plums, sloes and peaches are frequently recovered from archaeological waterlogged contexts. During an archaeological excavation in the city centre of Sassari (Italy), in 2007, a medieval well, dated at 1330-1360 AD, was discovered. The sediment appeared very rich in waterlogged plant remains and a consistent presence of Prunus endocarps, attributed to different species, was recorded. Thanks to the exceptional state of preservation of the remains, the morphological and morphometric analysis was performed. The discrimination among Prunus species is routinely based on visual evaluations of some traditional morphological characters of the endocarps. Currently, computer vision and image analysis techniques represent a more accurate, reliable and repeatable method to distinguish wild species from cultivated ones. Digital images, acquired with a flatbed scanner, were processed and analysed using the image analysis software KS-400 (Carl Zeiss Vision, Germany). A macro, specifically developed to measure endocarps of the Prunus L. genus, allowed measuring 33 morpho-colorimetric features and 80 elliptic Fourier descriptors (EFDs). In this work, the results obtained from the comparison between archaeological endocarps and the modern samples of Prunus collected in Sardinia, are presented. A clear statistical discrimination among 17 P. domestica, 111 P. domestica subsp. insistitia and 130 P. spinosa archaeological endocarps, was achieved. Moreover, from the comparison with the modern endocarps samples, the medieval ones were correctly identified with an overall percentage of 98.4 %. The LDA applied an archaeological Prunus endocarps preserved in waterlogged contexts have allowed us to investigate the taxonomic level of Prunus species present in the medieval period in Sardinia.