The openness of a flower and its number of flower‐visitor species

Using a sample of 1,403 flowering plant species, we tested the hypothesis that flower openness and flower‐visitor generalization level of a plant species correlate positively. The “flower‐visitor generalization level” L n of a flowering plant species n , here defined as number of flower‐visiting animal species attracted to the flowers of n in a given study site, varied enormously among plant species. Its frequency distribution was extremely skewed. Within a study site, L also increased with number of flower‐visitor species A . In order to correct for this, we expressed L relatively, as the proportion of the total flower‐visitor fauna in a study site that visited a given plant species (relative generalization level, L / A ). We listed the top‐10 most generalized species (both according to L and L / A ) in the “world”, i.e., out of our sample of 1,403 plant species. Flower openness is defined as accessibility to the interior of the flower. We placed the blossom classes of Fægri & van der Pijl along a gradient, albeit not very well defined, of decreasing flower openness (dish‐bowl, bell‐funnel, head‐brush, tube, gullet, flag) and tested for any relationship to their generalization level. The classes differed slightly but significantly in their level of L / A . Tube, bell‐funnel, and dish‐bowl had the highest generalization level and flag, gullet, and head‐brush the lowest. Thus, flower openness and generalization level were not correlated. We discuss other factors influencing generalization level such as accessibility to pollen and nectar, morphology and behavior of visitor, and species diversity of the different functional types of visitors.