CRITICAL PALEOBIOLOGICAL DATA FOR THE CONSERVATION OF ENDANGERED SPECIES: DAWN REDWOOD AS AN EXAMPLE

The plant genus Metasequoia has an abundant fossil record from every continent of the Northern Hemisphere since the Cretaceous; yet a single living species, Metasequoia glyptostroboides (Dawn Redwood) with a small native population restricted in south-central China, is listed as an endangered paleoendemic species facing serious challenges under the effects of anthropogenic climate change.

Two types of cuticles, the even type and the uneven type, have been characterized in its native living population with the vast majority of trees having uneven type cuticles. The even type is rarely found: Only a single tree in Paomu Village, Luota Town, Longshan County, Hunan Province, China (the “Paomu Tree”) and occasionally from some high branches of mature trees or juvenile seedlings. On the contrary, fossils all over the world are represented by the even type until recent reports of rare occurrence of the uneven type in Miocene fossils from Yunnan and Inner Mongolia in China. Competing hypotheses exist regarding the origin and relationship of these two cuticular types–whether they were caused by mutation(s) of certain genes or by different ecological conditions. Whether the Paomu Tree is a relic of fossil ancestors or the result of environmental or developmental factors has critical implications in the conservation plan for this species. Characterization of different cuticular types and a better understanding of the origin, development, and evolution of the rare cuticular type observed in the Paomu tree will only come from paleobiology data. We applied a cleared leaf epidermis (CLE) method that partially removes mesophyll tissues to separate the adaxial and abaxial epidermises of both cuticular types in both modern and fossil samples. This method allows us to observe their micromorphological characteristics and accurately measure 3D dimensions of key epidermal features, which was difficult in uneven type cuticles by other methods. A quantitative study of cuticular types in an ancient Metasequoia population during the warming middle Miocene climate under near future CO₂ levels will not only solve the Paomu tree mystery but also help better manage the conservation of the Dawn Redwood and other critically endangered plant species under a rapid rate of anthropogenic climate change.