INTRODUCTION Mahonia (Berberidaceae), a basal eudicot lineage, ranks as the second largest genus in the family, comprising approximately 100 species distributed across subtropical to temperate regions of East Asia and North America. The genus exhibits a classic East Asia-Western North America (EA/WNA) disjunction. Notably, Mahonia preserves abundant leaf fossil records in Cenozoic strata of the Northern Hemisphere, reflecting its prolonged evolutionary history. Characterized by distinctive foliar architecture that differs markedly from other angiosperm groups, this genus holds significant potential as a invaluable biological proxy or model plant for investigating the formation of intercontinental disjunct distribution patterns. Its unique morphological traits and biogeographic history provide critical opportunities to trace genus-level morphological evolution and spatio-temporal dynamics against the backdrop of global tectonic movements and climatic shifts.

RATIONALE Through comprehensive morphological surveys of extant Mahonia species, we established a novel leaf architecture classification framework designed for application to fossil leaf typology. This system aims to elucidate the genus’ foliar evolutionary trajectory since the Cenozoic and unravel the historical processes underlying its intercontinental disjunct distribution.

RESULTS Traditionally taxonomist divides Mahonia into two groups based on venation patterns: the palmately veined Group Orientales and the pinnately veined Group Occidentales. Building upon previous studies, we analyzed leaf architecture across 46 extant species and developed a refined subclade classification system using four diagnostic traits: leaflet margin type, serration density (teeth per edge), serration height, and leaflet length-to-width ratio. The Group Oriental was subdivided into seven foliar types (Microphylla, Japonica, Cardiophylla, Bodinieri, Polyodonta, Fortunei, and Nervosa), while the Occidental clade yielded six types (Chochoco, Dictyota, Volcania, Pumila, Lanceolata, and Aquifolium), accompanied by a diagnostic key. Distributional analyses revealed that within Group Orientales, geographic range expands with increasing serration height, whereas in Group Occidentales, distribution range correlates positively with serration density. The framework’s utility was further validated through taxonomic reclassification of two disputed fossil specimens, demonstrating its applicability to paleobotanical studies.

CONCLUSION Our refined foliar classification system for Mahonia represents a significant advancement in precision and granularity over previous systems. This framework holds substantial promise for standardizing Cenozoic leaf fossil typology across the Northern Hemisphere, while providing critical insights into the genus’ foliar evolution and the historical assembly of its intercontinental disjunct distribution pattern.

Retrieval and line drawings of leaf architecture of Mahonia