Pollen and androecium morphology of the neotropical genus Abatia Ruiz & Pavon (Salicaceae) and their systematic implications

Abatia is a small genus of 11 species in the Salicaceae that occur preferentially in high-elevation regions and has two centers of diversity, the Andes Mountains and the Campos de altitude of the Atlantic Forest. The present study aims to investigate the pollen and androecium morphology in Abatia species, contributing to the systematics of the group. Eight species (A. americana, A. angeliana, A. mantiqueirensis, A. mexicana, A. microphylla, A. parviflora, A. spicata, and A. stellata) were studied from herbarium material. Measurements and pollen characterization were performed by using light (LM) and scanning electron microscopy (SEM) while stamens and staminodes were analyzed only by SEM. Morphological variation was investigated by multivariate statistical analysis. Abatia constitutes a stenopalynous group with all studied species sharing isopolar, small, circular ambipolar, prolate-spheroidal to prolate (P/E = 1.05–1.43) pollen grains in monads. The apertures are zonocolporate, 3-colporate, with long and narrow colpi as ectoapertures and well-defined lalongate endoapertures. The exine is tectate, microreticulate, 0.55–1.15 µm thick, slightly thicker at the apocolpium. Statistical analysis reveals two clusters: Group 1 is formed by species from the Atlantic Forest, and Group 2 by Mexican and Andean ones. All species usually have fewer than 20 stamens per flower with a striate surface and glabrous, basifixed anthers with longitudinal, extrorse dehiscence. Staminodes are present in almost all species (lacking in A. angeliana) and have a glabrous and reticulate surface.