It might seem like the words “cannabis,” “hemp,” and “marijuana” are thrown around interchangeably. In reality, cannabis falls under two functional groups — hemp and marijuana. In the United States, plants with <0.3% of THC (tetrahydrocannabinol) are considered hemp. Any plant THC concentrations that are higher than 0.3% THC is considered marijuana.

Marijuana is divided into strains and typically assigned to one of three categories; “Sativa”,” Indica” or “Hybrid”.“ Sativa is characterized by uplifting and psychotropic effects. Indica reportedly has more relaxing and sedative effects. Hybrids are the result of breeding Sativa and Indica types, supposedly resulting in intermediate outcomes. Most cannabis users have a preference of the kind of strain they prefer depending on the experience they want to have, which makes these classifications important to consumers.

However, Cannabis is incredibly genetically diverse and most studies that have examined genetic variation within strains have discovered substantial genetic, morphological, and chemical variation. Recent research found only a moderate correlation between the genetic structure of marijuana strains. It reported that marijuana strain names often do not reflect a meaningful genetic identity3. Due to the lack of federal regulations, many Cannabis ‘strains’ lack the level of standardization that producers and consumers are accustomed to with other crop plants, such as genetically well-defined grape or banana varieties.

In the absence of proper genetic characterization, some attempts have been made at chemotype classification of cannabis ‘strains’ based on terpenes. Female Cannabis inflorescences (the main product of medical and recreational Cannabis) are covered in glandular trichomes which accumulate and secrete cannabinoid and terpene-rich resin. While cannabis users value the pharmacologically active cannabinoids of medical grade cannabis. Cannabis resin also contains a variety of terpenes, which are responsible for the characteristic smell and flavor of cannabis flowers. Differences between the pharmaceutical properties of different Cannabis strains have been attributed to interactions (or an ‘entourage effect’) between cannabinoids and terpenes making them a critical component of strain identity.

What are Terpenes?

Terpenes are a large and diverse class of organic compounds, produced by a variety of plants, but are particularly common in pine trees. Terpenes have a strong odor and some studies have shown that they protect the plants that produce them by deterring herbivores and by attracting predators and parasites of herbivores. Terpenes and terpenoids are the primary components of the essential oils of many types of plants (while the term terpenoids is often used interchangeably with “terpenes” terpenoids are modified terpenes containing additional functional groups). An essential oil is a concentrated hydrophobic liquid containing volatile (easily evaporated at normal temperatures) chemical compounds from plants. An essential oil produced by a plant is not “essential” or required for the plants survival. It is “essential” in the sense that it contains the “essence of” the plant’s fragrance—the characteristic fragrance of the plant from which it is derived. In fact the majority of the terpenes found in plants are classified as ‘secondary’ compounds (‘secondary’ because they are not required for basic life functions), that have evolved in plants as a result of selection for increased fitness in a specific environment.

Most of the terpenes found in Cannabis are hydrocarbons (hydrocarbon is an organic compound consisting entirely of hydrogen and carbon), which are the direct products of terpene synthase (TPS) enzymes. In plants, a family of terpene synthases (TPSs) is responsible for the synthesis of the various terpene molecules within the plant.

Several terpenes, including myrcene (a monoterpene), β-caryophyllene (a sesquiterpene), and α-humulene (a sesquiterpene) are the most common among cannabis strains. Other popular compounds include α-pinene (a monoterpene), limonene (a monoterpene), linalool (a monoterpene), bisabolol (a sesquiterpene) and (E)-β-farnesene (a sesquiterpene). Some of these terpenes are quite common in plants. For example, over 200 species of plants produce linalool (a monoterpene), mainly species from the Mint family (mints and herbs), Laurel Family (laurels, cinnamon, rosewood), and Citrus family (oranges, lemons). Myrcene (also a monoterpene) is also found in several plant species, including hops (Humulus lupulus, Cannabaceae), lemongrass (Cymbopogon, Poeaceae), thyme (Thymus serpyllum, Lamiaceae), and mango (Mangifera indica, Anacardiaceae).

Some terpenes (like the ones described above) are common and easy to identify in Cannabis strains. However, there are several ways terpene profiling remains challenging. Many terpenes (especially sesquiterpenes), remain difficult to identify. Additionally, there is substantial variation in terpene composition within Cannabis strains and even within individual plants. Different plant organs produce different quantities of terpenes and terpene composition may change over time as the plant develops and matures. The environment (temperature, water, or UV stress) in which a plant is grown may also influence terpene composition.

In sum, there are several challenges and opportunities for using terpene profiles as “chemotypes” to identify Cannabis strains:

  1. Some terpenes (especially sesquiterpenes), remain difficult to identify. This means that reports of terpene profiles in Cannabis strains may include unknown compounds, rely on unconfirmed identification, or present incomplete profiles.
  2. To improve reproducibility of terpene profiles in Cannabis, terpene profiles should be extracted from a variety of Cannabis genotypes/individuals grown under controlled environmental conditions (controlled temperature, humidity, light etc.)
  3. Terpene profiles should be analyzed over the course of plant development (during seedling, pre-bud, and flowering stages) and from plant tissue collected from multiple organs (stems, leaves, inflorescences).

Full list of scholarly sources mentioned in this article:

  1. Small E, Cronquist A. 1976. A Practical and Natural Taxonomy for Cannabis. Taxon, 25(4): 405-435. https://doi.org/10.2307/1220524
  2. Sawler J, Stout JM, Gardner KM, Hudson D, Vidmar J, Butler L, et al. 2015. The genetic structure of marijuana and hemp. PloS one, 10: e0133292. https://doi.org/10.1371/journal.pone.0133292 PMID: 26308334
  3. Lynch RC, Vergara D, Tittes S, White K, Schwartz CJ, Gibbs MJ, Ruthenburg TC, deCesare K, Land DP, Kane NC. 2016. Genomic and Chemical Diversity in Cannabis. Critical Reviews in Plant Sciences, 35:5-6, 349-363, DOI: 10.1080/07352689.2016.1265363
  4. Russo EB. 2011. Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects. British Journal of Pharmacology, 163: 1344–64. https://doi.org/10.1111/j.1476-5381.2011.01238.x PMID: 21749363
  5. Booth JK , Bohlmann J. 2019. Terpenes in Cannabis sativa – From plant genome to humans. Plant Science, 284: 67-72. https://doi.org/10.1016/j.plantsci.2019.03.022
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