Preliminary insight of pollen morphology of the Amazonian members of subtribe Columneineae (Gesneriaceae): details of morphological variation and pollen types

Columneinae, a morphologically diverse Neotropical group of Gesneriaceae Rich & Juss. ex DC., is strongly supported as a monophyletic, but many of the genera are weekly supported and lack diagnostic characters at the generic level. Predominantly distributed in the Andes and Amazon biomes, this group has not been evaluated from a palynological context. To address this gap and initiate comprehensive pollen studies within Columneinae, we conducted analyses on 28 species belonging to the genera Centrosolenia Benth., Chrysothemis Decne., Columnea L., Drymonia Mart., Glossoloma Hanst., Lesia J.L.Clark & J.F.Sm., Nautilocalyx Linden., and Trichodrymonia Oerst. Pollen grains were subjected to acetolysis, measurement, and light microscopy, with select species also examined under scanning electron microscopy. Quantitative data underwent statistical analysis tailored to the sample size and multivariate analysis. Variability was observed in size, shape, aperture type, aperture number, ectoaperture length, endoaperture shape, and exine ornamentation. The diverse morphological features led to the identification of distinct pollen types within Columneinae clades. Our findings suggest that eurypalynous pollen grains define most Columneinae and that stenopalynous pollen grains define Chrysothemis; however, comprehensive palynological studies involving a broader array of species within the subtribe are imperative to enhance our understanding of its palynology.