Above is an image of a tree fern frond plant fossil called Diplazites unita (Brongniart, 1822) Cleal, 2015. This plant fossil dates to the Carboniferous (Pennsylvanian) Period between 354 and 290 million years ago. It was found Mazon Creek, Illinois, USA. Like most fossils found at this locality, it was inside a nodule. The layer to fossil was found is the Francis Creek Shale.
The fossil was on display in the Evolving Planet section of The Field Museum of Natural History in Chicago Illinois, USA as of August 2020. Accession number is PP1015. They have quite an extensive collection of Mazon Creek fossils at the exhibit.
The Field Museum produced a visual PDF of some of the fossils found at Mazon Creek. It can be found at this link:
References:
Brongniart, A. (1822): Sur la classification et la distribution des végétaux fossiles ‒ Mémoires du Muséum d’Histoire Naturelle, 8
Cleal, C. J. (2015): The generic taxonomy of Pennsylvanian age marattialean fern frond adpressions. ‒ Palaeontographica, Abteilung B, 292: 1–21.