Iridoid is a class of compounds present in plants or animals. Chemically, it is a cyclopenta-(c)-pyran monoterpenoid, and usually exists as glycoside in a limited number of plant families. Biogenetically, iridoid may serve as intermediates in the biosynthesis of alkaloids. Iridoids taste bitter and are usually easy to dissolve in water. A total of 800 iridoids have been identified from plants and animals as of today. Of these, only about 80 iridoids are aglycone (no-sugar).