Format: ORAL

Peter K. Endress1

1 Institute of Systematic and Evolutionary Botany, University of Zurich, Zurich, Switzerland

Payer was a pioneer in the microscopic study of floral development based on detailed drawings of different developmental flower stages across many angiosperms. He recognized patterns that appeared to be similar in young stages. Some of these were interpreted as indicating systematic relationships. He assumed that in these flowers the development of the androecium was centrifugal. Only in polyandrous Magnoliales and Ranunculales did he find a centripetal pattern. Later authors improved the observation techniques and the systematic interpretation by phylogenetic analyses. Hirmer worked along similar lines (1918). As a new tool he used microtome sections, which allowed more precise images. Corner emphasized the systematic importance of centrifugal androecia, and unlike other workers, he assumed that this feature was phylogenetically basal, as it occurred in many families of mainly tropical distribution (1949). Corners view also influenced some later macrosystematists to assume that a number of angiosperm orders together were to be treated as the new angiosperm class Dilleniidae. However, with molecular systematic studies it later was shown that the class Dilleniidae had to be discarded (2018). Further progress was the use of scanning electron microscopy for flower development (Endress 1972) and the use of synchrotron radiation x-ray tomography microscopy for visualizing the inside of fossil flowers (Friis et al. 2014). Progress came also with the focus on still earlier developmental stages, when the developing flowers did not yet have any shape, but were only expressed as an activated meristem, only visible using stained microtome sections. Phylogenetic improvement came with global molecular phylogenetics, at first with the gene rbcL (Chase et al. 1993), and then continuously enriched up to the inclusion of all three plant genomes (Soltis et al. 2018). This, in turn, greatly helped to improve the knowledge of structural flower evolution.