Permineralized Ferns from the Middle Eocene Princeton Chert. I. Makotopteris princetonensis Gen. et Sp. Nov. (Athyriaceae).

The occurrence of numerous anatomically preserved specimens of an extinct filicalean fern in the middle Eocene Princeton chert from southern British Columbia, Canada, provides the basis for characterizing a new genus and species of the Athyriaceae. Fossils include narrow horizontal rhizomes with a radial amphiphloic dictyostele and internodes up to 1.5 cm long. Fronds are monomorphic. Adventitious roots are diarch and display a parenchymatous cortex. Stipes diverge in a radial fashion and display two hippocampiform bundles at the base. Distally, the bundles unite into a single trace, and pinnules are produced in an opposite to subopposite arrangement. The stipe, rachis, and pinnules display a continuous U-shaped groove on the adaxial surface. Sori of annulate sporangia are borne below veins on swollen receptacles. The sporangia are characterized by a vertical annulus and a narrow, elongated stalk. Spores are monolete and ellipsoidal, with a psilate exine and a distinctly spiny perispore. Makotopteris princetonensis gen. et sp. nov. significantly increases our knowledge of the fossil record for the Athyriaceae and documents that essentially modern athyrioids were present in the flora of North America by the early Tertiary.