Anatomically Preserved Ferns from the Late Cretaceous of Western North America. II. Blechnaceae/Dryopteridaceae

Permineralized rhizomes and stipe bases of filicalean ferns occur in the Upper Cretaceous (Campanian) Horseshoe Canyon Formation near the town of Drumheller in southern Alberta, Canada, and these provide an opportunity to describe the first anatomically preserved Mesozoic species of Blechnaceae/Dryopteridaceae. The two new fossil species also provide evidence that modern stelar architecture and stipe anatomy evolved in these families before the end of the Mesozoic. Midlandia nishidae gen. et sp. nov. has an apparently ascending radial rhizome from which stipes diverge in a helical pattern that approaches a 5=8 arrangement. The dictyostele is made up of amphicribral meristeles, and stipe traces consist of two hippocampiform bundles that flank three to four smaller circular bundles. The rhizome of Wessiea oroszii is somewhat smaller, with a dictyostele of five to seven cauline meristeles, from which stipe traces diverge as a pair of hippocampiform bundles. In both species, gaps in the stele are initiated by the divergence of a root trace, whereas stipe traces separate from the sides of the meristeles that flank the gap. The new species show numerous anatomical similarities to living blechnoid and dryopteroid ferns and strongly support hypotheses that these highly derived ferns originated before the Upper Cretaceous.