Pollen morphology of Titanotricheae, Beslerieae, and Coronanthereae (Gesnerioideae, Gesneriaceae): the importance of qualitative and quantitative data

Gesnerioideae comprises herbaceous plants, shrubs, or occasionally small trees. It includes 77 genera and more than 1200 species in the New World tropics, divided into five tribes: Titanotricheae, Napeantheae, Beslerieae, Coronanthereae, and Gesnerieae. We investigated the pollen morphology of Titanotricheae (monospecific, Titanotrichum oldhamii), Beslerieae (Besleriinae, four spp.), and Coronanthereae (Coronantherinae, three spp.; Mitrariinae, three spp.) using light microscopy (LM) and scanning electron microscopy (SEM). Pollen grains were described qualitatively and quantitative data were analysed through descriptive and multivariate statistics. The pollen grains of the analysed tribes differ mainly in their size (small, small to medium, medium), type and number of apertures (3[4]-colpate or 3-colporate; endoaperture circular, lalongate or lolongate), exine thickness (very thin, thin or thick), and exine ornamentation (microverrucate, microreticulate or reticulate). The qualitative (pollen description and pollen key) and quantitative data (descriptive and multivariate analysis) allowed us to infer that there is more similarity between the pollen grains of Coronanthera (Coronantherinae, Coronanthereae) and Beslerieae. Concurrently, the monotypic genus Rhabdothamnus (Coronantherinae, Coronanthereae) is more closely related to the monotypic genera Titanotrichum (Titanotricheae), Asteranthera, Mitraria and Sarmienta (Mitrariinae, Coronanthereae). In addition, this study described the pollen morphology of seven of the 11 studied species for the first time, increasing knowledge about the group. The qualitative and quantitative pollen data contribute to a more accurate delimitation of the genera and species within the Gesnerioideae tribes.