MORPHOLOGY AND ULTRASTRUCTURE OF THE PERMIAN TAENIATE POLLEN GENERA HAMIAPOLLENITES AND VITTATINA

Taeniate pollen form a morphologically distinct assemblage of 20-25 fossil pollen genera and over 100 recognized species united by possession of thick stripes in the pollen wall. Recovered from every continent and in rocks ranging in age from the Early Carboniferous to the Cretaceous, with its greatest diversity in the Permian, taeniate pollen document an early phase of explosive diversification among seed-bearing terrestrial plants. Despite their ubiquity and biostratigraphic utility, taeniate pollen remain poorly understood. Most taeniate pollen taxa have been identified only from grains dispersed in sediments, but taeniate pollen have been identified in pollen organs or in micropyles of ovules/seeds. These fossils demonstrate that Paleozoic taeniate grains were produced by at least three different groups of seed plants—conifers that are extant, and peltasperms and glossopterids that are extinct. The shapes of all phylogenetic trees for seed plants strongly support the independent evolution of taeniate pollen in these three groups.

Only nine species of taeniate grains in six genera have been examined ultrastructurally using transmission electron microscopy (TEM). However none are from North America or from the Early Permian making any new information important. In this study we document the morphology and ultrastructure of two common and widespread genera, Hamiapollenites Wilson, 1962, emend. Tschudy et Kosanke, 1966 and Vittatina (Luber, 1940) Wilson, 1962, based on dispersed pollen grains from the Wellington (Leonardian) and Flowerpot (Guadalupian) formations of Oklahoma. We use single-grain techniques to examine numerous examples of both genera using light microscopy, (LM), scanning electron microscopy (SEM), TEM, and focused-ion beam scanning electron microscopy (FIB-SEM). The agreement between TEM and FIB-SEM sections are investigated. Results are compared to previous analyses of taeniate pollen sections, including Vittatina, from the Late Permian of Russia and Australia, and are contrasted with extant gnetalean taeniate forms. Our results have implications for identifying close relatives and group-assignments and ultimately for integrating pollen into character-based phylogenetic hypotheses.