Indole-3-acetic acid (
IAA) is the most common, naturally-occurring,
plant hormone of the
auxin class. It is the best known of the auxins, and has been the subject of extensive studies by plant physiologists. Chemically, IAA is a
carboxylic acid in which the
carboxyl group is attached through a
methylene group to the C-3 position of an
indole ring. In appearance, IAA is a colorless solid.