Pollen cones and in situ pollen of Aegianthus Krassilov from the Middle Jurassic of East Siberia, Russia

Abstract

The paper documents in detail the morphological and epidermal characters of the pollen cones and in situ pollen of Aegianthus based on the study of specimens from the Prisayan Formation (Middle Jurassic) in the Irkutsk Basin (Siberia, Russia). An emended diagnosis is provided and a lectotype is selected for the type species, A. sibiricus, since a holotype/lectotype was not indicated in the previous publications of this species. Resin bodies are found in sporangiophores of A. sibiricus for the first time. The number of sporangia is specified as 10–12 per sporangiophore. This species differs from other Aegianthus species in smooth periclinal cell walls and lacking papillae on the subsidiary cells of the stomata in the abaxial epidermis of the peltate head. A new species, A. irkutensis, is described from the same Prisayan Formation of the Idan locality in the Irkutsk Basin. Unlike A. sibiricus, the cells of the outer epidermis of A. irkutensis are strongly papillate. A. irkutensis differs from other Aegianthus species by smaller resin bodies, numerous and longer sporangia. Pollen cones of both A. sibiricus and A. irkutensis were found in association with leaves of Sphenobaiera. The pollen of A. irkutensis are similar to those of A. sibiricus in morphology and ultrastructure. Pollen grains are boat-shaped, monosulcate. The exine surface is psilate or scabrate in the light microscope, and scabrate to granulate in SEM; the infratectum consists of large granules or columella-like elements. The exine ultrastructure of the Aegianthus pollen under study implies a ginkgoalean or gnetophytalean affinity.