THE ROLE OF HYDROPTERIS-PINNATA GEN ET SP-NOV IN RECONSTRUCTING THE CLADISTICS OF HETEROSPOROUS FERNS

Large segments of intact plants that represent a heterosporous fern ha ve been discovered within an aquatic plant community from the Late Cre taceous St. Mary River Formation near Cardston in southern Alberta, Ca nada. Branching rhizomes of Hydropteris pinnata gen. et sp. nov. are 1 -2 mm wide. They produce fronds at intervals of 2-12 mm and bear numer ous elongated roots. Fronds, up to approximately 6 cm long, are pinnat e with subopposite to alternate pinnae that exhibit anastomosing venat ion. Large, multisoral sporocarps occur at the junctures of the rhizom e and frond rachides. Both microsporangiate massulae and megaspore com plexes occur within each sporocarp. Megaspore complexes are assignable to the sporae dispersae genus Parazolla Hall. Microspores are trilete , smooth-walled, and are embedded in episporal material of the massula e. A numerical cladistic analysis indicates that the heterosporous aqu atic ferns are monophyletic, and not as closely related to either schi zaeaceous or hymenophyllaceous ferns as they are to some other filical eans. Systematic revisions are proposed to reflect newly recognized cl adistic relationships within the heterosporous clade, and character or iginations in the evolution of heterosporous aquatic ferns are evaluat ed. Hydropteridaceae fam. nov. is proposed, and included with Salvinia ceae and Azoflaceae in the Hydropteridineae subord. nov., and the Hydr opteridales Willdenow.