The endosperm is an essential part of the seed that sustains embryo development and reserve storage. Several genes that are involved in endosperm differentiation and that have domains of expression arranged along a conserved antero-posterior axis have been isolated in Arabidopsis and in cereals. Endosperm polarity is controlled maternally by chromatin-remodeling complexes. Endosperm development appears to be predominantly under epigenetic controls that might be linked with its evolutionary origin.