New species of Sphenobaiera Florin (Ginkgoales) from the Lower Cretaceous of Transbaikalia

Two new species of Sphenobaiera from the Baisa locality and Chernovskoe coal mine (Lower Cretaceous, Transbaikalia) are described. The cuticle of these plants inhabiting different environments differs significantly. Leaves of S. starukhiniae sp. nov. have a very thin cuticle, almost not sunken, open, nonprotected stomata, while the leaves of S. vitimica sp. nov. have relatively thick and strong cuticle, well-developed papillae overhang the sunken stomata. Guard cells of both species usually have fine radial striations. Apparently, the first plant dwelt in wet habitats, and the second, in the areas with a temporary shortage of water. This reconstruction is confirmed by sedimentological data, coal-bearing sediments (where S. starukhiniae sp. nov. was found) formed in swampy areas, carbonate deposits (S. vitimica sp. nov. was collected in marls of the Baisa locality), in the droughty one. It is not improbable that the cuticular features revealed of these two species contributed to more efficient water exchange and allowed plants to exist in these different environments.