Corolla micromorphology in 12 plant species with different pollination systems

Background: Floral microstructure, with multiple functions, is very important in pollination biology. Questions: Are the expected general characteristics of corolla micromorphology fulfilled in the selected species with different pollination systems? Studied species: Agave americana, Arbutus unedo, Aristolochia paucinervis, Cestrum nocturnum, Cytinus hypocistis subsp. macranthus, C. ruber, Dianthus lusitanus, Grevillea robusta, Musa x paradisiaca, Nicotiana glauca, Stellaria media and Teucrium fruticans. Study site and dates: Southern Spain, 2017-2019. Methods: Floral micromorphological characters were studied by light and scanning electron microscopy and analyzed using different statistical tests. Results: The adaxial side of the corolla lobes in melittophilous, myrmecophilous, psychophilous and sapromyophilous species showed papillose cells, and the same was true of the sphingophilous species Cestrum nocturnum and hummingbird -pollinated Nicotiana glauca. In contrast, tabular cells were observed in the perching -pollinator ornithophilous species Grevillea robusta, the two studied chiropterophilous species, and autogamous Stellaria media. In addition, corolla mesophyll was thicker in chiropterophilous species. Furthermore, differences were detected in cell turgidity (in protogynous Aristolochia paucinervis) and in mesophyll thickness between male and female flowers (Cytinus). Conclusions: Papillose cells were present in corollas in physical contact with pollinators, as expected, but also appeared in corollas of some other species without such contact. We recommend that studies of dichogamous and unisexual species include comparisons of corolla micromorphology between sexual states, as differences may exist in cell turgidity or mesophyll thickness. We also caution against the widespread view that certain types of pollinators do not mechanically interact with the epidermal surface of the corolla.