Introduced by Pierre Franchomme in 1975 and formalized in the European Union in 2006 with the adoption of the regulation REACH, a chemotype (sometimes chemovar) is a chemically distinct entity in a plant

Plant

Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

 or microorganism

Microorganism

A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...

, with differences in the composition of the secondary metabolites. Minor genetic

Genetics

Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....

 and epigenetic changes with little or no effect on morphology may produce large changes in the chemical phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

.

A good example of a plant with many chemotypes is Thymus vulgaris

Thymus vulgaris

Thymus vulgaris or common thyme is a low growing herbaceous plant, sometimes becoming somewhat woody. It is native to southern Europe, where it is often cultivated as a culinary herb....

. While largely indistinguishable in appearance, specimens of T. vulgaris may be assigned to one of six different chemotypes, depending on whether the primary component of the essential oil

Essential oil

An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...

 is thymol

Thymol

Thymol is a natural monoterpene phenol derivative of cymene, C10H14O, isomeric with carvacrol, found in oil of thyme, and extracted from Thymus vulgaris and various other kinds of plants as a white crystalline substance of a pleasant aromatic odor and strong antiseptic properties...

, carvacrol

Carvacrol

Carvacrol, or cymophenol, C6H3CH3, is a monoterpenoid phenol. It has a characteristic pungent, warm odor of oregano and a pizza-like taste.- Natural occurrence :...

, linalool, geraniol

Geraniol

Geraniol is a monoterpenoid and an alcohol. It is the primary part of rose oil, palmarosa oil, and citronella oil . It also occurs in small quantities in geranium, lemon, and many other essential oils. It appears as a clear to pale-yellow oil that is insoluble in water, but soluble in most common...

, thujanol-4 or terpineol

Terpineol

Terpineol is a naturally occurring monoterpene alcohol that has been isolated from a variety of sources such as cajuput oil, pine oil, and petitgrain oil. There are three isomers, alpha-, beta-, and gamma-terpineol, the last two differing only by the location of the double bond...

. Such chemotypes may be indicated as Thymus vulgaris ct. thymol (red thyme), or Thymus vulgaris ct. geraniol (sweet thyme), etc. Such an indication has no taxonomic standing, also see ecotype

Ecotype

In evolutionary ecology, an ecotype,Greek: οίκος = home and τύπος = type, coined by Göte Turesson in 1922 sometimes called ecospecies, describes a genetically distinct geographic variety, population or race within species , which is adapted to specific environmental conditions.Typically, ecotypes...

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