Floral epidermal structure and flower orientation: Getting to grips with awkward flowers

The petal epidermis has been found to be important in mediating flower-pollinator interactions. Structures produced on the petal surface, in particular cone-shaped papillate (or conical) cells, have been shown to enhance bumblebee preference for flowers. One reason for this increase in preference is that the conical cells facilitate efficient handling of flowers. This is particularly clear when flower architecture requires bees to land on a vertical surface. We therefore tested the hypothesis that flowers that are held vertically show a greater tendency to produce conical cells. Analysis of 183 species finds that there is no significant relationship between the structures on the petal surface and flower orientation. We discuss the multifunctional properties of conical cells and other floral surface structures that may mean that other factors are of equal or greater importance in the relationship between pollinators and petal epidermal form.