XVI International Botanical Congess

This paper focuses on a particular layer of the pollen wall which develops on the proximal face of the endexine, prior to vacuolate stage. It was described under different terms such as granular-fibrillar layer or radial oriented fibrillar vesicles, referring to its ultrastructure. This granular layer has often been interpreted as part of the endexine or the intine. During development, however, the granular material shows an ontogeny that is different from both intine and endexine. Observations suggest that its formation is mediated by the ER units that are in close connection with the plasmalemma. Our ontogenetic observations from several species are used to illustrate the widespread occurrence of this layer and its homologous nature throughout the angiosperms. A phylogenetic hypothesis is suggested to explain the current observations.