Chemotype

A chemotype, from chemical type, is a chemically distinct variant of a plant population within a species, characterized by a specific dominant secondary metabolite profile. Chemotypes are defined by the composition of the plant's essential oils or other secondary metabolites rather than by visible morphological traits. They represent a chemical phenotype that can reflect genetic differences, environmental influences, or an interaction of both.

Identification is usually performed by analytical methods such as gas chromatography–mass spectrometry (GC-MS) to determine the relative abundance of constituents in the plant's essential oil or extracts. A species may contain several chemotypes, each named for its hallmark compound, for example thymol-type thyme or carvacrol-type thyme; in Cannabis sativa, chemotypes have been described by dominant cannabinoids (THC, CBD, etc.).

Chemotypes may be relatively stable across generations under similar growing conditions, but environmental factors such as soil, climate, harvest time, and plant part used can shift the chemical profile. Thus chemotypes are not necessarily equivalent to botanical varieties or cultivars, which are defined by genetics or horticultural traits alone.

Applications of the chemotype concept include taxonomy, pharmacognosy, agriculture, and essential oil production. It helps identify appropriate plant material for medicines or fragrances and informs breeding and cultivation strategies. The concept is also used in chemotaxonomy and biodiversity studies to understand chemical diversity within a species.