Anatomical features of pollinia and caudicle in Epidendrum (Orchidaceae; Epidendroideae)

Abstract

The structural diversity of pollinia is one of the most relevant characters for the species classification in Orchidaceae. In this study, we analyzed the development of the pollinia and caudicle in Epidendrum species belonging to the subgenus Amphyglottium, one of the groups with the most variable morphology of the genus. These species have different pollination strategies (e.g., presence vs. absence of nectar) and grow in different types of habitat. Floral buds and flowers at anthesis were collected, and the usual methodology for performing anatomical studies, scanning microscopy, and confocal microscopy following established protocols. Our investigations revealed that the studied species have bithecal anthers and each theca has two pollinia and two caudicles. No interspecific variation was observed regarding the formation of the male gametophyte, indicating that is a stable character for the genus: the archesporial cells undergo a meiotic process that originates microspores, which remain united in tetrad and pass through asymmetric mitosis to form viable pollen grains. The caudicle is of the appendicular type and shows the male gametophyte formation.