Cuticle micro- and ultrastructure of Suturovagina Chow et Tsao (Cheirolepidiaceae): Taxonomic and palaeoecological implications

• Cuticles of the controversial genus Suturovagina were studied with multiple methods.
• The genus is characterized by extremely thick cuticle and unique stomatal structure.
• It differs markedly from Pseudofrenelopsis and other genera of the Cheirolepidiaceae.
• The stomatal apparatus bears tiers of subsidiary cells with guard cells at the bottom.
• Cuticle micro- and ultrastructures provide new evidence for an xerothermic climate.

Heterophyllous coniferous genera belonging to the family Cheirolepidiaceae are not always easily distinguished from one another morphologically. The taxonomically controversial genus Suturovagina from the Cretaceous of East China was studied by ultra-thin sectioning and examination under scanning and transmission electron microscopes. A detailed comparison between this genus and Pseudofrenelopsis was made based on cuticle micro- and ultrastructure as well as gross morphology. Suturovagina intermedia is among the few fossil coniferous plants for which cuticle and stomatal structures have been examined using both scanning and transmission electron microscopes and reconstructed using statistical data. Despite a slight overlap in gross morphology of leafy shoot , Suturovagina intermedia is well distinguished from Pseudofrenelopsis and all other cheirolepidiaceous conifers in cuticle and stomata micro- and ultrastructure, especially in the very deep stomatal chamber composed of tiers of subsidiary cells. The characteristic stomatal structure and the extremely thick cuticle with a wavy polylamellate layer in the cuticle proper also provide additional evidence for an xerothermic environment for the plant-bearing formation. The informative results of this study suggest that the potential taxonomic and palaeoecological significance of these features should not be neglected.