Plant hormones—or phytohormones—are chemical molecules that modulate one or more physiological processes of a plant. In animals, hormones are often produced in specific glands and circulated via the circulatory system. However, plants lack hormone-producing glands.

Hormones can be classified into three main types based on their chemical structures: steroids, peptides, and amines. Their actions are mediated by the specific receptors they bind to on target cells.

Hormones are classified into four main groups: steroids, eicosanoids, amino acid-based derivatives, and peptide hormones.
Steroids and eicosanoids fall under the category of lipid-soluble hormones. Steroids are derived from cholesterol and feature four interconnected carbon rings with variable side chains. Notable examples include estradiol from ovaries and testosterone from testes, exemplifying the critical roles of these lipid-soluble hormones in reproductive physiology. Eicosanoids, derived...