Exine ultrastructure of in situ Protohaploxypinus from a Permian peltasperm pollen organ, Russian Platform

The fine morphology and exine ultrastructure are studied in pollen grains of Protohaploxypinus-type, which were extracted from a pollen organ of Permotheca striatifera from the upper Permian (Lopingian) Isady locality (Vologda Region, Russia). The pollen grains are bisaccate and striate, with up to ten proximal ribs. The ectexine and endexine differ in ultrastructure and electron density. The ectexine is alveolate; the endexine is more electron-dense and appears homogeneous, though some indices of layering were observed under higher magnifications. The sacci appear protosaccate. Areas that flank the body are a diminished and more regular version of the sacci. In ribs, the ectexine includes an outer continuous layer, a thinner underlying alveolate layer, and an inner layer. Grooves between the ribs either retain the inner homogeneous ectexinal layer resting on the endexine or are lined by the endexine alone. The distal face of the body is covered by the endexine alone. The obtained data are compared with available ultrastructural information on pollen grains of the Protohaploxypinus-type of different origins and with that on other peltasperm pollen types such as Vittatina, Vesicaspora and Cycadopites. The diversity of species of Permotheca is outlined.