Conantiopteris schuchmanii, gen. et sp nov., and the role of fossils in resolving the phylogeny of Cyatheaceae s.l.

A permineralized tree fern from the Lower Cretaceous (Aptian) near Cottonwo od, California is described as Conantiopteris schuchmanii gen. et sp, nov. The specimen, 23.2 cm long and 11.7 cm wide, shows helically arranged persi stent frond bases embedded in adventitious roots, and is clothed by multice llular trichomes, A parenchymatous pith with mucilaginous cells and sclerot ic nests is surrounded by an amphiphloic distyostele, parenchymatous inner cortex, and outer sclerenchymatous cortex. Sclerenchyma also surrounds the cauline vasculature and leaf traces. Medullary and cortical bundles are abs ent, Phloem contains both axially elongated and tangential sieve elements. Frond bases are oval in outline with three vascular bundles, including an u ndulating abaxial are and an adaxial pair. Protoxylem of the stipe is endar ch and is associated with cavity parenchyma. These characters are indicativ e of tree fern affinities. A cladistic analysis using trunk characters of b oth living and fossil tree ferns was conducted to help establish relationsh ips of the new species and other fossil ferns, and to test hypotheses of ge neral tree fern relationships. Additional analyses of living taxa only were also performed. Results from the analysis using both living and fossil tax a compare favorably with those that included only living species when eithe r morphological characters or molecular sequences of the chloroplast gene r bcL are utilized. Although there are variations in the topologies of the va rious trees, results indicate that the new genus is nested among a paraphyl etic assemblage of dicksoniaceous, lophosoriaceous, and metaxyaceous specie s that subtend a monophyletic Cyatheaceae s.s.