The spore/pollen walls of embryophytes have multiple layers and components that are laid down in a regulated manner during spore/pollen development. Layers containing the macromolecule sporopollenin are the component enabling the resistance of the spore/pollen wall to numerous environmental factors that make life on land challenging. Sporopollenin is highly resistant to physical, chemical and biological degradation procedures.
Consequently, its precise chemical composition, structure and biosynthetic route have not yet been ascertained (Meuter-Gerhards et al. 1999). Traditional convention asserts that sporopollenin is a polymer of carotenoid esters (Cronk 2009). However, modern purification, degradation and analytical techniques have shown that it is comprised of polyhydroxylated unbranched aliphatic units with small quantities of oxygenated aromatic rings and phenylpropanoids (Ahlers et al. 1999; Domínguez et al. 1999).