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Abstract: The araucarian pollen grain Cyclusphaera radiata Archangelsky is emended based on newly discovered material from the Piedra Clavada Formation of Albian age in Santa Cruz province, Argentina. The general morphology and ultrastructure of the pollen were studied by means of transmitted light, scanning, and transmission electron microscopy. C. radiata is discoid with an equatorial thickening and two large opposite apertures, with radial thickenings in one of them and two central apertural occlusive opercula-like structures. Beneath there is a thick amorphous electron-dense nexine. The combination of characters seen in this pollen type is very unusual, and no parallels are known in fossil or extant gymnosperm grains. Functional interpretation of the apertural exine suggests that the radial thickenings and apertural membranes were involved in harmomegthy, the opercula-like structures in germination, and the apertural nexine perhaps as a strengthening layer. A hypothetical pollination mechanism is also presented for C. radiata. The paleobiogeography of this taxon shows that during the Mesozoic, the plants that produced these grains inhabited an extensive area of Gondwana that included South America, Africa, India and Antarctica. [Copyright &y& Elsevier]

Abstract: A new araucarian pollen cone Alkastrobus peltatus gen. et sp. nov. is described from the Anfiteatro de Ticó Formation (Baqueró Group) of Aptian age in Santa Cruz province, Argentina. The pollen cones are mostly compressions and their microsporangia contain the well-known Cyclusphaera Elsik pollen. The morphology, anatomy and ultrastructure of the pollen cones along with the pollen grains were examined under light, scanning and transmission electron microscopy. An affinity with the Araucariaceae is established on the basis of microsporophyll anatomy and morphology, and comparison of Cyclusphaera with other araucarian pollen grains. In Patagonia during the Cretaceous Period, plants producing Araucariacites, Balmeiopsis and Cyclusphaera pollen lived together. All three types of pollen are found inside microsporangia. Araucariacites, the only type that has survived to the present day, is found in the extant genera Araucaria and Agathis. The new genus confirms the broad diversity that Araucariaceae attained during the Early Cretaceous within western Gondwana. [Copyright &y& Elsevier]