Several Plant Taxa with Reticulate-Veined Leaves Through the Mesozoic Time Period

Venation architectures and cuticular micromorphology of leaf fossils play important roles in higher-level taxonomic segregation, as these characters are broadly fixed within major plant clades. Some common fossil plant taxa are characterized by similar-shaped leaves or leaflets and anastomosing venation to such an extent that examples have commonly been assigned to the wrong taxon in past studies where fragmentary or ill-preserved material is available. Our reanalysis of the macro- and micromorphology of Sagenopteris and Anthrophyopsis leaves reveals important differences that help segregate taxa even on the basis of incomplete specimens. Anthrophyopsis has distinctive alignments of vein cross-connections in the outer lamina and paracytic stomata consistent with those of Bennettitales. Sagenopteris has more consistently evanescent midribs and surficial anomocytic or stephanocytic stomata with weakly modified subsidiary cells. Considering the putatively close relationship of Caytoniales (Sagenopteris) and Bennettitales (Anthrophyopsis) resolved as members of the ‘glossophyte’ clade in some past phylogenetic studies, cuticular features suggest that they are not closely related. Temporo-spatial analysis of Anthrophyopsis suggest it confined to the Upper Triassic, while Sagenopteris surviving the end-Triassic mass extinction and became one of the dominant gymnosperms in the aftermath of biotic crisis but also failed to reach the Cenozoic period.