Mediterranean Spurge

Euphorbia characias

Like all members of the Euphorbia family Spurges have unisexual flowers. In other words they both male and female flowers on the same plant. Wikipedia tells me that the male flowers have a stamen and the female flowers have a pistil. The flowers do not have sepals, petals or nectar.
Nectar that attracts pollinators is held in a separate cup like structure below.

Euphorbias are the only plants known to have this kind of flower head.

Spurges also have a milky white sap which is irritant and believed to have evolved to deter grazing animals.