The endosperm is a tissue produced inside the seeds of most flowering plants following double fertilization. In angiosperms, a double fertilization event initiates the development of two distinct structures, the embryo and endosperm. The endosperm plays an important role in supporting embryonic growth by supplying nutrients, protecting the embryo, and controlling embryo growth by acting as a mechanical barrier during seed development and germination. Its structure and function in the mature dry seed is divergent and specialized among different plant species.

The cells of the endosperm are triploid (3n) and arise from the fusion of the polar nuclei (2n) with the sperm nucleus (n) through a double fertilization event. The development of the endosperm is divergent among plant species. Nonetheless, the comparison of endosperm development between cereals and Arabidopsis displays some similar features. The endosperm is the outermost living layer in the seeds, and its function is influenced by both the embryo and the surrounding environment. The endosperm responds to environmental factors, inducing the expression of Arabidopsis hormone metabolism genes in response to imbibition.

The endosperm also mediates the transfer of nutrients from the mother plant to the embryo, acts as a location for gene imprinting, and is responsible for aborting seeds produced from genetically mismatched parents. In angiosperms, the endosperm contains hormones such as cytokinins, which regulate cellular differentiation and embryonic organ formation. Cereal grains, such as wheat, rice, and corn, are rich in endosperm and are important sources of food for humans and animals.