Distribution and occurrence characteristics of barnyard grass (Echinochloa spp.) species in mainland China's farmlands

Barnyard grass ( Echinochloa spp.) is one of the most damaging weeds in global agricultural systems. In China, its species composition and distribution patterns remain poorly understood due to ambiguous taxonomic treatments. In this study, we addressed these knowledge gaps by mapped the geographical distribution of Echinochloa species and assessed their floristic characteristics and harmfulness. Our approach integrated herbarium specimen review, extensive field surveys, and calculations of harm and niche indices. A total of 12 Echinochloa species and varieties were identified in Chinese farmland. The Yangtze River basin and southern regions hosted 11 taxa, with the exception of Echinochloa oryzoides (Ard.) Fritsch, whereas northern regions contained only five species and varieties: E. oryzoides , Echinochloa oryzicola (Vasing) Vasing, Echinochloa crus-galli var . praticola Ohwi, Echinochloa crus-galli var. mitis (Pursh) Peterm . , Echinochloa crus-galli (L.) P. Beauv. All 12 taxa were observed in rice fields, with 7 presented in maize fields. Clear geographic differences were evident in both harmfulness and dominant species. In rice fields, the dominant taxa included E. oryzicola , E. crus-galli , E. crus-galli var. mitis , Echinochloa crus-galli var. zelayensis (H.B.K) Hitch, E. glabrescens . Northern rice fields were dominated by E. oryzicola , while southern rice fields exhibited a co-dominance pattern of E. crus-galli , E. crus-galli var. mitis , E. glabrescens , E. crus-galli var. zelayensis . In maize fields, E. crus-galli was widespread, but north-south differentiation was observed: Echinochloa colona (L.) Link occurred more frequently in the south, whereas E. crus-galli var. praticola prevailed in the north. The observed distribution patterns were associated with multiple environmental and anthropogenic factor, including climatic factors (e.g., temperature, moisture), cropping systems (paddy vs. maize), species-specific ecological characteristic, and anthropogenic dispersal. These results provide a high-resolution baseline dataset that may inform future, spatially explicit studies and support the development of context-specific management strategies for Echinochloa species in major agroecosystems across mainland China.