Exine morphology and ultrastructure of Duplicisporites from the Triassic of Italy

摘要

A morphological study of dispersed Circumpolles pollen grains from the Upper Triassic of the Southern Alps has been initiated with the genus Duplicisporites. Individual pollen grains were studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Seen with SEM the pollen surface is finely verrucate with low verrucae of different sizes. A sub-equatorial continuous rimula is clearly visible. The proximal trilete scar is small and indistinct. TEM images reveal a bi-layered exine. The ectexine is formed by numerous small, closely packed, granulae subdivided by irregularly-spaced cavities. In the region of the subequatorial canal, the ectexine becomes thinner, about 1/3 of the usual thickness. At places, the ectexine is slightly separated from the underlying endexine. The endexine is prominent and significantly darker than the ectexine. It is homogeneous and of constant thickness. On the basis of its older age, with respect to Classopollis, the present ultrastructural dataset provides information on the possible origin of cheirolepidiaceous-type morphology.