Morpho-anatomical affinities and evolutionary relationships of three paleoendemic podocarp genera based on seed cone traits
Abstract Background and Aims The three relict genera Pherosphaera, Microcachrys and Saxegothaea in Podocarpaceae produce quite distinct seed cone types in comparison to other genera and does not form a clade along with Acmopyle. The detailed seed cone morpho-anatomy of these three relict genera and affinities with other podocarps are poorly known. This study aims to understand the seed cone morpho-anatomy and affinities among these three disjunct relict genera and with other podocarps. Methods We comparatively analysed the seed cone morpho-anatomical traits of the three podocarps genera and used ancestral state reconstruction to understand the evolution of these traits. Key Results We described the seed cone morpho-anatomical structures of the three relict genera in detail. The three genera produce aggregated multiovulate cones. Both Microcachrys and Saxegothaea has an asymmetrical free cup-like epimatium. Both species of Pherosphaera lack epimatium. The ancestral state reconstruction implies that the presence of epimatium is an ancestral trait in podocarps and independently lost in Pherosphaera and Phyllocladus. The seed cones are fleshy in Microcachrys and non-fleshy in Saxegothaea and Pherosphaera. The seed cone macrofossils of both extinct and living podocarps also show the presence of epimatium and fleshiness in podocarps. Conclusions Altogether, the morpho-anatomy suggests Pherosphaera, Microcachrys and Saxegothaea present affinities with each other and other podocarps but the reconstruction of ancestral seed cone in Podcarpaceae is quite complex due to multiple convergent evolutions of several structures. These structures (e.g. epimatium, aril, receptaculum) are of low taxonomic value but of great evolutionary and ecologically significance and are responsive adaptations to ever-changing environmental conditions.