Analysis of leaf economics sheds light on the heterophylly and ecological strategies of Paleocene Ginkgo leaves from Henan Province, China

The palaeoecology of Ginkgo through deep time, including its ecophysiology and heterophylly, remains poorly understood due to the limitation of quantitative methods. In this paper, we report well-preserved leaves of Ginkgo henanensis sp. nov. from the Paleocene Dazhang Formation of Luanchuan, Henan Province, China. Our understanding of the ecophysiology and heterophylly of the genus has been improved by the discovery. These fossils are distinguished by heterophyllous leaves that can range in morphology from bilobed to multi-lobed forms. Thus, unlike other Cenozoic Ginkgo with entire-margined leaves, this is the first well-established Cenozoic taxon that has exclusively lobed leaves similar to Mesozoic-type ginkgos. A useful leaf ecophysiological functional trait that offers quantitative insights into morphological heterophylly and the mechanism of leaf shape selection is the dry leaf mass per area (LMA) of Ginkgo. Leaf shape changes, including the evolution of heterophylly, are linked to functional adaptation. There are two groups of LMAs for four fossil G. henanensis specimens: 120.9 g/m(2 )to 131.3 g/m(2), and 184.5 g/m(2) to 187.4 g/m(2). The results of the reconstructed fossil LMAs, which serve as quantitative evidence of G. henanensis' heterophylly, also point to the existence of various leaf survival strategies within G. henanensis. Additionally, both groups of G. henanensis have LMAs that are higher than those of extant Ginkgo biloba, indicating that this species has a slower return ecological strategy than its current equivalent. This strategy may have helped to decrease the rate of nutrient cycling, which supported Ginkgo to thrive in a wider variety of ecological niches in the Paleocene than it does today. These findings close a knowledge gap in the evolution of Ginkgo.