According to LIPID MAPS classification, sterol lipids are further divided into sterols, steroids, bile acids and derivatives. Sterols occur in the membranes of plants, animals, and microorganisms and are termed phytosterols, zoosterols, and mycosterols, respectively. While cholesterol (CHO) is the major sterol of vertebrates, ergosterol (ERG) plays a key role in fungi. Plants usually possess more complex sterol compositions.