ABSTRACT
This chapter presents a brief account of pollen morphological variation observed in various groups of modern and fossil groups of gymnosperms. Fossil gymnospermous pollen have been extensively used in palynostratigraphy, which are of great significance in the exploration of fossil fuels such as coal and oil. Paleobotanical evidence shows that fossil pollen of almost all groups of gymnosperms such as cycads and conifers in addition to extinct pteridosperms have been well preserved in the sediments dating back to the Devonian period. The most outstanding characters of the pollen grains of the cycadofilicales are their large size and pluricellular structure. In Cycadales the pollen grains are small, broadly ellipsoidal, boat shaped, with a single deep longitudinal furrow reaching from end to end, essentially as in the grains of Ginkgo. The pollen grains of the Ginkgoales, like those of the cycads, are notable for their single deep and broad unprotected furrow and their lack of prothallial tissue.
