A carbohydrate in which two *monosaccharide
units are joined by a glycosidic bond. The commonest disaccharide in plants is *sucrose
. Other common disaccharides include *maltose
. Less common disaccharides include the nonreducing trehalose, composed of two glucose units linked by an α(l-l) glycosidic bond. This is the main free sugar in Selaginella species. Some disaccharides have specific functions, such as the translocation function of sucrose, while others (e.g. cellobiose) are breakdown products of larger molecules.