The history of the Portulaca oleracea aggregate in the Emilia-Romagna Po Plain (Italy) from the Roman Age to the present

Portulaca oleracea L. is a cosmopolitan synanthropic species, of uncertain origin, known in Italy since the Roman Age. The aim of this work is to reconstruct the history of P. oleracea aggregate in the Emilia-Romagna Po Plain, by discovering the microspecies that have lived in this region. A qualitative study was carried out to determine the microspecies documented in the archaeological sites of Emilia-Romagna, from the Roman to Medieval/Renaissance periods. A comparison between archaeological seeds and recent and present records was made by sampling in historical herbaria and field collections. Seven different microspecies were identified: Portulaca papillatostellulata, P. trituberculata, P. cypria, P. sativa, P. oleracea (all hexaploid); P. granulatostellulata and P. nitida (both tetraploid = 4x). They are distinguished on the basis of seed coat morphology. The findings in archaeological sites and in the present collections are discussed. Two independent events of European colonization could be proposed: First to arrive were the hexaploid (6x) species, followed by the tetraploid species. In future, the application of similar analyses to the well-preserved archaeobotanical remains of purslane, particularly the microspecies from America, could be a good way to understand the history of this interesting species aggregate from a chronological and geographical standpoint.