Comparative morphology of fossil and extant leaves of Nelumbonaceae, including a new genus from the Late Cretaceous of Western North America

We describe in detail the foliar architecture of extant Nelumbo and propose a new genus, Exnelumbites Estrada-Ruiz, Upchurch, Wolfe & Cevallos-Ferriz, for recently discovered leaf macrofossils from the Upper Cretaceous (Campanian-Maastrichtian) Olmos Formation of Coahuila, Mexico and Jose Creek Member of the McRae Formation of south-central New Mexico, U. S. A. The fossils described here consist of centrally peltate leaves with 12-13 actinodromous primary veins that terminate in broad glandular teeth of the chloranthoid type. No secondary veins are present on the midvein, and tertiary veins are organized in an alternate percurrent to reticulate pattern. Areolation is of variable shape with four to six sides. The fossil leaves are placed within Nelumbonaceae on the basis of their orbicular shape and centrally peltate organization, the presence of a funnel-form lamina, and especially the absence of secondary venation along the midvein, but are interpreted to be more primitive than extant Nelumbo in having no central disk, a smaller number of primary veins, less highly organized tertiary venation, and predominantly non-hexagonal areolation. The presence of chloranthoid teeth in the fossils is consistent with suggestions that the chloranthoid tooth type is basal to both Proteales and eudicots as a whole. The newly described leaves add to a growing diversity of plant macrofossils from the Cretaceous that are more closely related to Nelumbo than any other extant genus, but are more primitive in their vegetative and reproductive morphology.