Pollen morphology of Poaceae (Poales) in the Azores, Portugal

Abstract

The objective of this study was to expand knowledge on the Poaceae and morphologically describe pollen grains of species occurring in the Azores Archipelago, Portugal. Pollen grains from each species under study were subjected to standard acetolysis, mounting of at least three permanent slides of each species for observations and measurement of pollen grains under light and scanning electron microscope. With regard to pollen morphology, all pollen grains were arranged as monads, with a single pore-type aperture – monoporate, featuring annulus and operculum; and outline in polar view circular, sub-circular and ovalate. Most species featured pollen size small, except for Agrostis stolonifera with pollen size very small, Brachypodium sylvaticum with pollen size medium, Zea mays with pollen size large. Species endemic to the archipelago show ornamentation pattern ranging between areolate-microechinate, microechinate, microrugulate-microechinate and verrucate-microechinate, most of which feature exine surface areolate-microechinate. Among endemic species, Rostraria azorica stood out for its oblate-spheroidal shape, whereas most species showed prolate-spheroidal shape.