What is "phytochemical"

Phytochemical \Phy`to*chem"ic*al\, a. Relating to phytochemistry.
--R. Hunt.

a. Of or pertaining to phytochemistry n. 1 Any chemical substance characteristic of plants. 2 Any chemical or nutrient derived from a plant source; a phytonutrient.

Phytochemicals are chemical compounds that occur naturally in plants (phyto means "plant" in Greek). Some are responsible for color and other organoleptic properties, such as the deep purple of blueberries and the smell of garlic. Phytochemicals may have biological significance, for example carotenoids or flavonoids, but are not established as essential nutrients. There may be as many as 4,000 different phytochemicals.