Abstract
E. albomarginata, E. Capitellata and E. hyssopifolia together attract over 200 spp. of insect visitors of their cyathia; bees that are oligolectic on Euphorbia figure prominently among these in both number of species and abundance of individuals. E. albomarginata, a mat-forming plant, attracts 3 times as many species as the erect species E. capitellata and E. hyssopitfolia. All insects pollinate the plants by mess and soil behavior. Bees are more effective pollinators than other insects by virtue of their frequent movement on cyathia and their ability to carry pollen. Bees are abundant on the large, conspicuous cyathia of E. albomarginata and E. capitellata, but are less common on the sma-l, inconspicuous cyathia of E. hyssopifolia. Plant growth form (mat vs. erect) probably exerts a major influence on the number of insect visitors, but cyathial size determines the abundance of effective pollinators. These species of Euphorbia have not evolved in response to their associated bees, despite the important role of the bees in the pollination ecology of the plants.

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