This is from wikipedia

In general, it is accepted that there are five major classes of plant hormones, some of which are made up of many different chemicals that can vary in structure from one plant to the next.

The chemicals are each grouped together into one of these classes based on their structural similarities and on their effects on plant physiology. (following this is a list of the five major classes)

Other plant hormones and growth regulators are not easily grouped into these classes; they exist naturally or are synthesized by humans or other organisms, including chemicals that inhibit plant growth or interrupt the physiological processes within plants. Each class has positive as well as inhibitory functions, and most often work in tandem with each other, with varying ratios of one or more interplaying to affect growth regulation.

(I highlighted the word many and added sentence in brackets)