Domestication of broomcorn millet (Panicum miliaceum) is one of the most significant events in prehistoric East Asia, providing sufficient food supply for the explosive growth of Neolithic populations and the transition into complex societies. However, to date, the process of broomcorn millet domestication is still largely unknown, partly due to the lack of clear diagnostic tools for distinguishing between millet and its related wild grasses in archaeological samples. Here, we examined the percentage of silicified epidermal long-cell undulated patterns in the glume and palea from inflorescence bracts in 21 modern varieties of broomcorn millet and 12 weed/feral-type Panicum ruderale collected across northern China. Our results show that the percentage of ηIII patterns in domesticated broomcorn millet (23.0% ± 5.9%; n = 63) is about 10% higher than in P. ruderale (10.8% ± 5.8%; n = 36), with quartiles of 17.2–28.3% and 5.1–15.5%, respectively. Owing to the increase in ηIII pattern percentage correlates significantly with a decrease in the grain length/width ratio, in the absence of exact wild ancestors of broomcorn millet, the characterization of phytolith differences between P. ruderale and P. miliaceum thus becomes an alternative approach to provide insight into origin of broomcorn millet.

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Neolithic rice remains were recovered from a mixed rice–millet farming area in China outside the original centers of rice farming. Whether the rice remains were the result of local cultivation or obtained through trade remains unclear. Rice paddy fields are direct evidence of local cultivation. In this study, phytolith samples from the Zhangwangzhuang site were analyzed. The discriminant function distinguished 17 of 30 samples in the suspected paddy field area as rice paddy fields with an average probability of 74%; The proportion of rice bulliform phytoliths with ≥9 scales indicated that rice (Oryza sativa) was still being domesticated and, moreover, six η-type phytoliths from broomcorn millet (Panicum miliaceum) were identified. These results suggested that the suspected paddy field at Zhangwangzhuang might be the earliest rice paddy field (ca. 6000 cal. BP) in northern China and that mixed farming was practiced here since the early Yangshao period. This study adopted discriminant analysis methods to discover ancient rice paddy fields, observed rice paddy fields outside the core rice origin area, and provided the earliest evidence regarding the development of mixed rice–millet farming in the upper Huai River region.