Acta Palaeobotanica 44(1): 3–35, 2004

Morphology and ultrastructure of some monosaccate pollen grains of Cordaitina Samoilovich 1953 from the Permian of Russia

Summary: Cordaitina pollen grains from three localities of the Perm Region (Kungurian Stage) of Cis Urals and Tunguska Basin (Kazanian? Stage) of Siberia were studied under LM, SEM, and TEM. The pollen grains are monosaccate, circular elliptical, with a small trilete or monolete scar, which is occasionally lacking. The saccus appears smooth under SEM, finely reticulate under LM, reflecting in transmitted light the interior partitions occasionally superimposed by the surface folds. The saccus is filled with rather loose alveolate structure with mostly radial ectexinal partitions that reach the endexine in the protosaccate type of pollen grains. Alternatively, the partitions, or some of them, are unrooted forming an intermediate protosaccate/eusaccate infrastructure. This variation is gradational rather than discrete and is correlated with the thickness of the saccus ectexine: the thicker sacci tend to be more definitely eusaccate. A finely punctate LM view of the corpus reflects a peculiar crochet like sculpture formed of interlaced threads or rugae (under SEM), which are confacered here as a diagnostic feature of the Permian Cordaitina. In TEM micrographs, the ectexine attenuates confacerably towards the polar regions, while its outermost layer, the tectum, becomes finely undulate forming the crochet like pattern. The innermost layer, or endexine, is relatively thin over the distal face and at the saccus/corpus border increasing proximally and attaining the maximal thickness towards the proximal scar. It is interrupted at the borders of the proximal laesurae. Distally the endexine appears dense and homogeneous, although proximally, and especially over the proximal scar, it becomes loose, layered, formed either of vaguely defined lamellae or of fine granules. This differentiation suggests an ontogenetic layering of the endexine. The ultrastructural data indicate proximal rather than distal germination placing the Permian Cordaitina in the prepollen grade. The potential palynotaxonomic significance of the type of sculpture, saccus infrastructure and apertural morphology is discussed.

Keywords: pollen grains, pollen ultrastructure, gymnosperms, cordaites, Permian, Russia