Pollen morphology applied to species delimitation of Myrsine (Myrsinoideae-Primulaceae)

Abstract

Myrsine, a genus in the family Primulaceae, includes closely related species whose taxonomic identification is difficult. Morphological analysis of pollen grains has provided key information for the classification of Primulaceae, helping clarify the taxonomy of several genera, subgenera, and species. However, a detailed study of pollen morphology in Myrsine was still lacking. Therefore, in this study, we investigated the potential of pollen characters to be used for the specific delimitation of Myrsine. Acetolyzed pollen grains were examined using light microscopy and non-acetolyzed pollen grains were analyzed by scanning electron microscopy. Pollen grains and monads of all analyzed species were isopolar, small to medium in size, and prolate spheroidal, subprolate, or prolate in shape, with (3)-4-colporate apertures, regular colpi or loxocolpi, and reticulate-granulate, granulate, rugulate-granulate, or microreticulate exine. Species considered difficult to identify based on other morphological traits were successfully distinguished using quantitative and qualitative pollen characters, confirming the importance of pollen morphology as a source of taxonomic information. Also, Myrsine stands out among genera of the subfamily Myrsinoideae because it shows great interspecific pollen variation, including two class sizes of pollen grains, three types of exine ornamentation, and exclusive loxocolporate pollen with inconspicuous endoapertures. This is the first report of loxocolporate pollen in Primulaceae.