The ultrastructure and reproductive significance of Monoletes (Pteridospermales) pollen

Abstract

The Carboniferous pteridosperm pollen type Monoletes is described from reproductive organs of differing preservational mode and stratigraphie occurrence. The sporoderm is constructed of two zones: an inner thin lamellated nexine and a thicker alveolate sexine. The ultrastructure of the sporoderm in the area of the proximal suture suggests that germination may have taken place from that region. Distal surface grooves are a consistent feature of the grains examined although grain ontogeny, preservation, and tapetal products may mask their presence. Features of sporoderm infrastructure suggest that Monoletes pollen grains may represent a type transitional between wind and insect pollination.