xylan

alt=|thumb|481x481px|Structure of xylan in hardwood. thumb|481x481px|Plant cell wall is composed of cellulose, hemicellulose, pectin and glycoproteins. Hemicelluloses (a heterogeneous group of polysaccharides) cross-link glycans interlocking the cellulose fibers and form a mesh like structure to deposit other polysaccharides.

Xylan (; ) (CAS number: 9014-63-5) is a type of hemicellulose, a polysaccharide consisting mainly of xylose residues. It is found in plants, in the secondary cell walls of dicots and all cell walls of grasses. Xylan is considered to be the second most abundant plant biopolymer, and the third most abundant polysaccharide on Earth after cellulose and chitin.