One of the five major plant hormones that play an important role in plant growth and development. Abscisic acid (ABA) is ubiquitous in higher plants; the highest levels are found in young leaves and developing fruits and seeds. Abscisic acid is also produced by certain algae and by several phytopathogenic fungi. It has been found in the brains of several mammals; however, animals probably do not produce abscisic acid but acquire it from plants in the diet.