 Euphorbias are the only plants known to have this kind of flower head.Nectar glands and nectar that attract pollinators are held in the involucre, a cup-like part below and supporting the cyathium head.The "involucre" in the genus "Euphorbia" is not to be confused with the "involucre" in family Asteraceae members, which is a collection of bracts called phyllaries, which surround and encase the unopened flower head, then support the receptacle under it after the flower head opens.