Palynology of Bromelioideae, a highly diverse subfamily within Bromeliaceae

Abstract Bromelioideae exhibits high variability in pollen characters and is therefore eurypalynous. Palynological studies have described numerous genera within the subfamily, contributing to a more precise circumscription at generic and infrageneric levels. However, most studies have focused on surface analyses or observations of the sporoderm in pollen grains lacking cytoplasmic content (lux obscuritas microscopy). As a result, characters describing internal structures that are not resistant to acetolysis, such as the intine, have been less frequently addressed. This study aimed to describe the pollen types found in Bromelioideae by analysing the sporoderm surface and stratification patterns using a combination of anatomical techniques, acetolytic treatment, and scanning electron microscopy. The results confirmed the palynological diversity of Bromelioideae, revealing variations in pollen size, shape, dispersal unit, aperture number, ornamentation, and infratectum types. Differences were also observed in sporoderm stratification, aperture type, and aperture margins. The intine exhibited remarkable diversity, being predominantly stratified into three layers, with distinct patterns observed in some species. A structurally unique feature was identified in diporate grains, here referred to as the pseudoannulus.