The ultrastructure of some Rhaetian Circumpolles from southern England Ultrastructure of some Rhaetian Circumpolles

The morphology and exine ultrastructure of Classopollis torosus, C. meyeriana and Geopollis zwolinskae are studied from the Cotham Member of the Lilstock Formation (Penarth Group) in southern England. The palynological assemblage that allows dating the deposits to the Rhaetian is outlined. Although the Circumpolles pollen grains under study show variations in the exine ultrastructure, some common characters support their origin from the same plant group, the Cheirolepidiaceae. An infratectum formed by large granulae arranged mostly in one row and sandwiched between the tectum and endexine is considered as the key character of the pollen grains under study. Ultrastructural transformations within Circumpolles are discussed. The origin of Classopollis-producing plants from any plant group with saccate pollen and alveolate ectexine is considered much less probable than from a group with non-saccate pollen with granular ectexine.