Osmunda cinnamomea (Osmundaceae) in the Upper Cretaceous of western North America: Additional evidence for exceptional species longevity among filicalean ferns

The discovery of numerous anatomically preserved fossils in Upper Cretaceou s sediments reveals that essentially modern osmundaceous ferns have inhabit ed southern Alberta, Canada, since the end of the Mesozoic. The Cretaceous fossils consist of small stems that are surrounded by leaf bases and advent itious roots. All of the features of the fossils fall within the ranges of variation for characters of living Osmunda cinnamomea L., and the fossils d isplay all of the specifically diagnostic anatomical characters for this sp ecies. These include an ectophloic, dictyoxylic solenostele that lacks leaf gaps in the phloem, C-shaped frond traces, frond bases with lateral stipul ar expansions, features of the endodermis, and disposition of sclerenchyma tissues in the stem and frond bases. A reexamination of extant specimens an d of previously described fossils from Neogene and Paleocene deposits clari fies the range of variation for specifically diagnostic characters and reve als the more or less continuous presence of O. cinnamomea L. in western Nor th America for at least 70 million years. This article provides an addition al example of a well-characterized fossil filicalean fern that can be confi dently assigned to a species with living representatives. It is becoming in creasingly clear that species longevity for homosporous pteridophytes can b e far greater, and species turnover may be far lower, than expected from ev olutionary models developed for flowering plants.