Anther wall formation, microsporogenesis and male gametogenesis of four closely related species in Astereae (Asteraceae): description, comparison and systematic implications

Abstract

The embryological features of microsporangiate wall formation, microsporogenesis and male gametogenesis in Aster subulatus, Kalimeris indica, Heteropappus arenarius and Erigeron annuus are described for the first time. Although external morphology might suggest that these four species differ from each another, we found no distinctly different embryological features. They all share similar characteristics, such as a tetrasporangiate anther, coexisting amoeboid and glandular tapeta, simultaneous cytokinesis (except for 12% occurrence of successive cytokinesis in E. annuus), 3‐celled mature pollen grains and endothecium of anther wall that does not develop fibrous thickenings. Based on the embryological data, we suggest that Kalimeris and Heteropappus may be included within Aster, and that Erigeron is closely related to Aster sensu lato.