Fossil evidence and ecological niche modelling reveal trait evolution and biogeography of the Ilex cornuta lineage

Abstract

Naturally occurring in the subtropical regions of China to Korea, Chinese Holly (Ilex cornuta Lindl. & Paxton, Aquifoliaceae), is widely cultivated as an ornamental plant. However, the origins of the phenotypical diversity of the species as well as its geographical history remain elusive. Here we report 50 exceptionally well-preserved fossil leaves of the I. cornuta lineage from the middle Miocene of South Korea. These fossils showcase delicate details, encompassing both adaxial and abaxial surfaces, as well as primary to quinternary venation patterns. The varied leaf morphologies, ranging from three to seven spines, demonstrate that these leaf morphologies of I. cornuta were established by the middle Miocene. Furthermore, fossil discoveries from the middle and late Miocene of Korea and China, coupled with the enduring presence of highly suitable habitats in Asia since the late Paleogene, suggest a longstanding persistence of the I. cornuta lineage in this region. The identification of closely related fossils from the Miocene to Pliocene of Europe implies potential floristic interchange between the continents, facilitated by the regression of the Turgai Strait in the Paleogene. This is consistent with the broad suitable habitat of the lineage, which once spanned Europe and Asia from the late Eocene to early Oligocene. Our study provides an example for integrating fossil records with ecological niche modelling to elucidate the biogeographical history of plants.