Chemotypes

A chemotype is a genetically distinct population or individual within a plant species (or other organisms) that produces a characteristic profile of chemical compounds, particularly secondary metabolites such as terpenes, alkaloids, or phenolics. Chemotypes are defined by a stable predominance of certain chemicals—often in essential oils or resin—while other traits may be similar or identical to those of related populations.

The occurrence of chemotypes arises from genetic variation that influences biosynthetic pathways, and these differences can be influenced by environmental factors such as soil, climate, harvest time, and cultivation practices. Some chemotypes are relatively stable across generations, whereas others may shift in response to changing conditions or stress. Chemotypes are not the same as visible morphological differences, and a single species can harbor multiple chemotypes with little external differentiation.

Common examples include Cannabis sativa, where chemotypes are frequently described by the ratio of delta-9-tetrahydrocannabinol (THC) to cannabidiol (CBD), resulting in high-THC, high-CBD, or intermediate chemotypes. In essential-oil producing plant families such as Lamiaceae, chemotypes differ in dominant terpenes—for instance thymol, carvacrol, linalool, or geraniol—leading to oils with distinct sensory and biological properties. Identification of chemotypes typically relies on chemical profiling using gas chromatography and mass spectrometry, often complemented by genetic data.

Applications of chemotype knowledge include quality control in essential oils, targeted breeding and cultivation, pharmacognosy, and regulatory considerations where chemical composition affects efficacy and safety. Chemotype is a concept distinct from cultivar or variety, emphasizing chemical composition rather than solely morphology.