Peltaspermalean seed ferns with preserved cuticle from the Upper Triassic Karamay Formation in the Junggar Basin, northwestern China

Abstract

Foliage of a new peltaspermalean seed fern is described on the basis of a large collection of well-preserved plant adpressions with cuticle from the Upper Triassic Karamay Formation in Xinjiang Province, NW China. Pinnae are lanceolate with undulate-dentate margins and with fascicular lateral veins in lobes. Tertiary veins are simple as are interfascicular veins that occur between fascicular lateral veins. Cuticles are thick, amphistomatic, with abaxial and adaxial cuticles being similar to each other and having clear costal and intercostal areas. Stomata are sunken and randomly distributed on both the abaxial and the adaxial cuticle. The stomatal complex is monocyclic and comprises 4–7 subsidiary cells. Papillae are present on ordinary cells and on subsidiary cells surround the stomatal aperture. The adaxial leaf surface has a stomatal index of 3.27 and an average stomatal density of 15permm2, whereas the abaxial surface has a stomatal index of 5.25 and an average stomatal density of 30permm2. This is the first report of the cuticular structure of Scytophyllum from the Junggar Basin, which now enables detailed comparison with other species of the genus from Eurasia. Analysis of the sedimentary succession containing Scytophyllum suggests a humid or seasonally dry environment, but the thick cuticles with sunken stomata and abundant papillae indicate that the plant was adapted to living in water-stressed conditions.