Crusgallin as a biomarker for Echinochloa crus-galli (L.) P. Beauv.: Preservation in Bronze Age charred seeds and application to archaeological sediments

Millets are receiving renewed attention due to their short growing cycles, resilience and role as fodder and summer cereals. As C4 plants adapted to arid and tropical environments, millets were domesticated in East Asia and Africa, with species such as broomcorn millet spreading into Europe during the Bronze Age. In European archaeology, millets are key indicators of crop diversification among human communities, including in northern Italy. Archaeological evidence of their use derives from charred grains, phytoliths and stable isotope and molecular biomarkers analyses. Among molecular biomarkers, miliacin (olean-18-en-3β-ol methyl ether) has been widely recognised as a biomarker for Panicum miliaceum (L.)/broomcorn millet detected in pottery, sediments and charred residues. Carbon enrichment typical of C4 plants in Middle Late Bronze Age human remains has often been linked to millet consumption, although wild panicoid grasses may also have contributed to these isotopic signals. Among wild panicoid grasses, generally more difficult to trace archaeologically, Echinochloa crus-galli (L.) P. Beauv./barnyard grass represents an exception since its charred grains have often been found. This study investigates crusgallin (taraxer-14-en-3β-ol methyl ether) as a potential biomarker for barnyard grass. Different anatomical parts of modern plants were chemically analysed to determine crusgallin distribution, and the data were used as reference for the study of sediments from the Middle Bronze Age site of Oppeano 4D, where byre-houses containing herbivore dung and plant bedding were identified. Archaeobotanical deposits yielded abundant barnyard grass seeds together with miliacin and crusgallin, suggesting that these biomarkers may derive from both plant remains and herbivore dung, additionally indicating millets as possible components of animal fodder.