Anther and pollen development and their relevance in delimiting the Neotropical species of the Malveae tribe (Malvaceae)

Abstract

Recent phylogenetic studies support the monophyly of the tribe Malveae, with floral morphology providing the main basis for clade delimitation. However, embryological data remain underexplored despite their potential contribution to phylogenetic inference. In this study, we analyzed the embryological development of 12 Neotropical Malveae species to investigate anther ontogeny, microsporogenesis, and microgametogenesis. Floral buds and flowers at different stages of development were collected, and standard methodologies for optical microscopy and confocal laser scanning microscopy were employed. The anther wall pattern corresponds to the dicotyledonous type, with unistratified epidermis, endothecium with ring thickening, an ephemeral middle layer, and a binuclear tapetum of the nonsyncytial invasive type. Microsporogenesis involves simultaneous meiosis, resulting in tetrahedral tetrads. After microspore maturation, microgametogenesis begins, with microspore undergoing asymmetric mitosis, giving rise to vegetative and generative cells. Mature pollen grains are bicellular and contain an abundance of starch. The uniformity in the developmental patterns observed among the analyzed species suggests the presence of shared characteristics that may serve as phylogenetic markers. This strengthens the evidence of a close evolutionary relationship among members of the Malveae tribe and highlights the importance of ontogeny in understanding phylogenetic relationships and delimiting clades in Malvaceae.