Comparative Pollination Ecology of Five European Euphorbia Species.

Premise of research. Flowers of the genus Euphorbia are arranged in a unique type of inflorescence called cyathia, packed into more or less dense synflorescences. These synflorescences can be showy or inconspicuous, suggesting different pollination strategies. Methodology. We described and compared the morphology, color, scent, and insect guilds visiting the synflorescences of five European Euphorbia species, two with inconspicuous synflorescences and three with showy ones. Pivotal results. All five species present their reproductive structures openly, with easily accessible nectaries. In the inconspicuous E. peplus and E. dulcis , there was little color contrast between the reproductive parts and the vegetative parts. Both species attracted low numbers of insects (Diptera and Hymenoptera), and these insects carried little (E. peplus) or no (E. dulcis) pollen. We did not detect any floral scent for E. peplus. In the showy E. amygdaloides , E. virgata , and E. verrucosa , the color of the reproductive parts and of the relatively large nectaries was standing out clearly against vegetative organs. These species attracted up to 14 times more insects (Diptera, Hymenoptera, Coleoptera) than the inconspicuous species, and these insects carried larger amounts of pollen on their bodies. In E. verrucosa , nearly half of the pollinators were sawflies from the genus Tenthredo feeding and mating on the synflorescences. All Euphorbia species except E. peplus were also visited by ants. However, the role of ants as pollinators remains to be tested. Finally, E. peplus and E. dulcis can reproduce without insect pollination, whereas among the showy species, E. virgata did not produce seeds when pollinators were excluded. Conclusions. We found that all study species had similar generalist pollination systems, with the showy species attracting significantly more insects and the inconspicuous species being largely independent of insect visits for reproduction. Our study tentatively indicates that the degree of entomophily seems positively correlated with showiness and size of attractive and rewarding organs. [ABSTRACT FROM AUTHOR]