auxin

Auxins (plural of auxin /ˈɔːksɪn/) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essential for plant body development. The Dutch biologist Frits Warmolt Went first described auxins and their role in plant growth in the 1920s. Kenneth V. Thimann became the first to isolate one of these phytohormones and to determine its chemical structure as indole-3-acetic acid (IAA). Went and Thimann co-authored a book on plant hormones, Phytohormones, in 1937.

Native auxins

Indole-3-acetic acid (IAA) is the most abundant and the basic auxin natively occurring and functioning in plants. It generates the majority of auxin effects in intact plants, and is the most potent native auxin.

There are four more endogenously synthesized auxins in plants.
All auxins are compounds with aromatic ring and a carboxylic acid group:

4-Chloroindole-3-acetic acid (4-CI-IAA)

2-phenylacetic acid (PAA)

Indole-3-butyric acid (IBA)

Indole-3-propionic acid (IPA)

For representatives of synthetic auxins, see: Auxin § Synthetic auxins.