This fossil leaf is from a tree belonging to the genus that includes the familiar sycamore tree of North America and the plane tree of Europe. This type of tree has been studied for its adaptability, with several species found to produce hybrids with one another (De Castro et al., 2013). Fossils of the genus Macginitiea have been found in Cretaceous rocks of Canada, USA, Japan, and Russia, as well as Paleogene and Neogene rocks of North America, Europe, and Asia (Huegele & Correa Narvaez, 2024). Because of its extended stratigraphic range and close similarity with the modern plane tree, it can be considered a good example of morphological stasis in the fossil record. This specimen shows the typical characteristics of Macginitiea wyomingensis leaves, including five narrow to triangular lobes separated by relatively deep sinuses, a serrate margin (although the teeth in this specimen are small), basal divergence of primary veins, and a chevron-like symmetric arrangement of the secondary veins (Huegele & Correa Narvaez, 2024). Manchester (1986) synonimyzed Macginitiea wyomingensis as a comb. nov. of the previously used taxon Platanus wyomingensis. Leaves of this species are among the most common plant remains in some fossil-bearing localities of the Green River Formation (Grande, 1984; MacGinitie, 1969).

References:

De Castro, O., Di Maio, A., Lozada García, J.A., Piacenti, D., Vázquez-Torres, M. and De Luca, P., 2013. Plastid DNA sequencing and nuclear SNP genotyping help resolve the puzzle of central American Platanus. Annals of Botany, 112(3), pp. 589-602. doi:10.1093/aob/mct134.

Grande, L., 1984. Paleontology of the Green River Formation, with a review of the fish fauna. Geological Survey of Wyoming, Bulletin 63, p. 333. (1st ed. 1980.)

Huegele, I.B. and Correa Narvaez, J.E., 2024. Revisiting the Iconic Macginitiea plant and its implications for biogeography, basilaminar lobe development, and evolution in Platanaceae. International Journal of Plant Sciences, 185(2), pp. 138-158. doi:10.1086/728411.

MacGinitie, H.D., 1969. The Eocene Green River flora of northwestern Colorado and northeastern Utah. University of California Publications in Geological Sciences 83, p. 140.

Manchester, S.R., 1986. Vegetative and reproductive morphology of an extinct plane tree (Platanaceae) from the Eocene of western North America. Botanical Gazette, 147(2), pp. 200-226.