SPORODERM ULTRASTRUCTURE IN EARLY CRETACEOUS PROANGIOSPERMS

Abstract

The exine ultrastructures of pollen extracted from sporangia of Loricanthus resinifer and Baisianthus ramosus from the Early Cretaceous Baisa locality (eastern Transbaikalia) were examined. The pollen are small, with a broad furrow and a granular (Baisianthus) or granular-columellar (Loricanthus) infratectum. In the apertural region, both a thin foot layer and endexine are revealed. The latter is homogeneous and irregularly thickened in Baisianthus and lamellate and uniform in thickness in Loricanthus. The presence of both granular and columella-like elements in the infratectum and the relative development of the foot layer and endexine distinguish the pollen grains under study from those in the majority of Mesozoic gymnosperms. The ultrastructural sporoderm characters in the investigated species agree with the proangiospermous evolutionary grade.