Self-pollination
A great deal of Euphorbia are hermaphroditic, which means they possess both female and male reproductive organs. Although most flowering plants are hermaphrodites, not all can self-pollinate. Eurphorbia, such as the poinsettia, can self-pollinate, and has five sperm producing stamen directly surrounding a single, egg-bearing pistillate. Many Euphorbia grow in extremely dry, desert conditions where pollination agents, such as insects and animals, are scarce. As a result, several Euphorbia species evolved to self-pollinate to perpetuate their species in case they couldn't cross pollinate.
Insects
Most Euphorbia plants are pollinated by insects. The plants' colorful features and perfumes attract insects such as bees, ants and beetles to feed on the nectar of the flowers. While feeding on the nectar, the insects rub against the pollen produced by the stamen and carry it off with them when the leave the plant. The insects carry the pollen to another plant and while they continue feeding, they unknowingly fertilize the flower's pistillate. The relationship between insects and flowers is ancient and is the most common means of pollination.
Animals
Animals such as birds, lizards and amphibians also contribute to Euphorbia pollination, much in the same way as insects. A study by ecologist Hector Godinez-Alvarez, a Universidad Nacional Autonoma De Mexico faculty member, on plant pollination by lizards revealed that lizards are extremely successful pollinators. Lizards forage in Euphorbia plants for nectar very slowly and take their time while feeding. This increases the chances of pollen spreading onto the lizards' snouts and also increases the chances of fertilization. A lizard's slow movements and long feeding time are what make it such a successful pollinator.
Wind Pollination
Wind pollination is a major technique implemented mostly by trees and scentless flowers. Flowers that produce pollen for wind don't produce nectar, which means they don't attract animals and insects. Wind pollinating plants generally grow closely together to maximize efficiency. Most Euphorbia plants don't have the luxury of leaving pollination to the wind, but the castor oil plant is one Euphorbia that does. This plant, which grows in great abundance in the South Mediterranean, is highly resilient to the elements and grows very tall for a Euphorbia -- in some cases, up to 39 feet. Other Euphorbia plants don't reach this height -- the poinsettia, for example, grows from 2 to 12 feet -- and the plants generally are found sparsely in arid areas. Because of this, the other Euphorbia produce nectar to attract insects and animals to maximize the possibility of reproduction.