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 f ilicalean fern in the middle Eocene Princeton chert from southern British C olumbia, Canada, provides the basis for characterizing a new genus and spec ies of the Athyriaceae. Fossils include narrow horizontal rhizomes with a r adial amphiphloic dictyostele and internodes up to 1.5 cm long. Fronds are monomorphic. Adventitious roots are diarch and display a parenchymatous cor tex. Stipes diverge in a radial fashion and display two hippocampiform bund les at the base. Distally, the bundles unite into a single trace, and pinnu les are produced in an opposite to subopposite arrangement. The stipe, rach is, and pinnules display a continuous U-shaped groove on the adaxial surfac e. Sori of annulate sporangia are borne below veins on swollen receptacles. The sporangia are characterized by a vertical annulus and a narrow, elonga ted stalk. Spores are monolete and ellipsoidal, with a psilate exine and a distinctly spiny perispore, Makotopteris princetonensis gen. et sp. nov. si gnificantly increases our knowledge of the fossil record for the Athyriacea e and documents that essentially modern athyrioids were present in the flor a of North America by the early Tertiary.