A plant's cuticle is the boundary layer between the plant and its environment, and is one of the key innovations that occurred during the evolution of land plants. Over the last 400 million years the plant cuticle has evolved to become a complex and multifunctional interface, consisting mainly of insoluble polymers such as cutin (a polyester matrix) and (in some species) cutan, plus polysaccharides such as cellulose. Waxes are a major component of the cuticle that are either embedded into the cutin matrix (intracuticular waxes) or deposited onto the cuticle surface (epicuticular waxes). The major function of the cuticle is to serve as a highly efficient barrier against uncontrolled water loss and to reduce leaching of organic and inorganic substances from the leaf interior, and waxes are the main determinants of these properties.