A new heterosporous plant from the Cretaceous of West Siberia

A heterosporous free-sporing plant is described from the Upper Cretaceous o f the Kern' River, West Siberia. The plant produced pinnate sporophylls wit h pinnules bearing a large solitary sporangium containing megaspores and mi crospores. The megaspores are numerous, in tetrahedral tetrads, with membra nous laesural flanges forming an apical neck and the lateral pockets filled with monolete microspores. The plant represents a distinct line in the evo lution of heterosporous pteridophytes with amphisporous sporangia retaining a great number of megaspores and developing an elaborate mechanism of join t dispersal of megaspores and microspores. (C) 1999 Elsevier Science B.V. A ll rights reserved.