Azolla reproductive structures in the Cenozoic of West Siberia

Reproductive structures (megaspore complexes and partly massulae) of 22 species of Azolla Lamarck (Azollaceae, Salviniales, Pteridophyta) are recorded from the Eocene–Holocene of West Siberia. Descriptions are provided and the distribution is traced for the species Azolla filiculoides Lamarck, A. incerta V. P. Nikitin, sp. nov., A. monilifera P. A. Nikitin ex P. I. Dorofeev, and A. tomentosa P. A. Nikitin from the section Azolla G. H. Mettenius, the species Azolla aspera P. I. Dorofeev, A. nana P. I. Dorofeev, A. nikitinii P. I. Dorofeev, A. pseudopinnata P. A. Nikitin, A. suchorukovii P. I. Dorofeev, and A. ventricosa P. A. Nikitin ex P. I. Dorofeev from the section Rhizosperma (F. Meyen) G. H. Mettenius, the species Azolla aculeata V. P. Nikitin, sp. nov., A. atava V. P. Nikitin, sp. nov., and A. cluthiana V. P. Nikitin, sp. nov. from the section Trisepta K. Fowler, as well as the species Azolla asiatica V. P. Nikitin, sp. nov., A. gracilis V. P. Nikitin, sp. nov., A. juganica V. P. Nikitin, sp. nov., A. macrocephala V. P. Nikitin, sp. nov., A. minuta V. P. Nikitin, sp. nov., A. sibirica P. I. Dorofeev, A. theganica V. P. Nikitin, sp. nov., A. tumida V. P. Nikitin, sp. nov., and A. verruculosa V. P. Nikitin, sp. nov., whose affinity to the sections Rhizosperma or Trisepta currently cannot be determined.