Cultivar
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A cultivar is a group of cultivated plants selected for particular characteristics and able to keep those characteristics when propagated by defined means. The word, a contraction of "cultivated variety", is governed by the International Code of Nomenclature for Cultivated Plants (ICNCP), which treats a cultivar as the basic unit of classification for plants in cultivation and requires it to be distinct from other cultivars, uniform in its selected traits and stable, so that those traits persist through the propagation used to maintain it.[1] A cultivar name pairs the botanical name with a cultivar epithet, as in Cannabis 'Finola'.
In Cannabis the cultivar sits among several overlapping ways of naming plant groups that are often confused. It differs from a landrace, a locally adapted population maintained by farmers without formal selection; from a botanical variety, a rank of the wild-plant nomenclatural code applied to naturally occurring forms; from the vernacular strain, a market term with no standing in either code; and from a chemovar, a grouping by measured cannabinoid and terpene chemistry rather than by breeding history. Most Cannabis sold as named "strains" has never been registered or verified as a cultivar, and genetic studies have repeatedly found that shared names do not guarantee shared ancestry.
Whether a plant group qualifies as a cultivar carries practical weight. It determines how the group can be protected under plant breeders' rights, how reliably a grower can reproduce it, and how conservation programmes weigh it against the landraces from which cultivars are ultimately drawn.
Definition and nomenclature
The cultivar concept applies to plants whose distinguishing features are held in place by cultivation rather than by natural range. Under the ICNCP a cultivar must be distinguishable from any other cultivar by one or more characters, uniform in those characters within the limits of its breeding system, and stable, so that the characters survive the cycles of propagation used to reproduce it.[1][2] Those requirements can be met by very different kinds of plant group: a seed-propagated line bred to a fixed type, a single clone multiplied from cuttings, or the controlled cross of two parent lines remade each generation to give a uniform result.
A cultivar is named by attaching a cultivar epithet to the name of the genus or species. The epithet is written in roman type inside single quotation marks with each word capitalised, as in Cannabis 'Finola' or Cannabis sativa 'Carmagnola'. Under the code, epithets coined since 1959 must be in a modern language rather than Latin, and those coined since 1996 are limited in length, which is why recent names read as ordinary words instead of botanical Latin.[2] Where several cultivars share a defined character they may be gathered into a cultivar Group, a formal category the code provides for the broad, loose assemblages that growers describe as a "family" or "line".[3]
This apparatus is separate from the botanical ranks used for wild plants. The International Code of Nomenclature for algae, fungi, and plants governs categories such as subspecies, variety (varietas) and forma, which describe naturally occurring variation and are anchored to herbarium type specimens. A cultivar is instead defined by human selection and documented by a standard description rather than a type specimen.[4][2] The word "variety" bridges the two codes and so invites confusion: in agriculture and plant-protection law a variety is in effect a cultivar, the unit a breeder registers, whereas in botany a variety is the wild-plant rank varietas. The two are set by different processes, and a single Cannabis plant can answer to both, belonging to the botanical variety indica while also, if bred to a stable type and registered, carrying a cultivar name.
Cultivar, landrace and botanical variety
The three formal ways of grouping Cannabis plants differ less in the plants themselves than in how the groups are made and kept. A landrace is a population that has adapted to a locality over generations of cultivation and reselection by farmers; because selection is loose and pollination largely open, it stays internally diverse and is recognised as a population, not as a single repeatable type.[5][6] That variability is not a defect but the mechanism by which a landrace keeps adapting to its place, and it is exactly what a cultivar gives up.[7]
A cultivar is the outcome of tightening that process. Deliberate selection, controlled pollination and a defined propagation method narrow a variable population down to a uniform, repeatable product.[7][3] The uniformity gained is also diversity lost, and that standing variation is what lets a landrace track a changing environment, a trade-off that underlies why landraces and cultivars are conserved differently (see below).
The botanical variety occupies a third position. It is a rank of the wild-plant code applied to naturally occurring forms set apart by heritable morphology and geography, such as the narrow-leaflet and broad-leaflet drug plants that a widely cited revision assigns to Cannabis sativa subspecies indica.[4][3] A botanical variety is not the product of a breeding programme, and naming one implies nothing about uniformity in the horticultural sense. The same population can therefore be described three ways over its history: as a wild or weedy botanical variety, as the landrace that farmers select from it, and as the cultivar eventually bred out of that landrace.
| Grouping | Governing code | Basis of the group | Within-group uniformity | Maintained by | Example |
|---|---|---|---|---|---|
| Cultivar | ICNCP | deliberate human selection | high; distinct, uniform, stable | defined seed or clonal propagation | Cannabis 'Finola' |
| Botanical variety (varietas) | wild-plant code (ICN) | heritable morphology and geography | not implied | natural reproduction in range | C. sativa subsp. indica var. afghanica |
| Landrace | none; informal | local adaptation under farmer selection | low to moderate; variable by design | farmer seed-saving and reselection | Hindu Kush charas landraces |
| "Strain" | none; vernacular | market and consumer naming | none guaranteed | commercial seed or clone lines | "OG Kush" |
| Chemovar / chemotype | none; chemical | measured cannabinoid and terpene profile | chemical, not genetic, by definition | re-measurement of chemistry | Type I, THC-dominant |
"Strain" as a vernacular term
The word most consumers use, strain, has no standing in either nomenclatural code. It is borrowed from microbiology, where it denotes a genetic line of a microorganism, and applied loosely to named Cannabis products.[citation needed] Its survival is commercial rather than botanical, and the names attached to it are not backed by the distinctness, uniformity and stability that a cultivar name asserts.[8]
Genetic surveys have shown how weakly these names track ancestry. A study genotyping marijuana and hemp found that plants sold under the same strain name were in some pairings less alike than plants carrying different names, and that a strain's advertised split between "sativa" and "indica" corresponded only weakly to its measured genome-wide ancestry.[9] A later study using a larger marker set recovered the same pattern, with samples of a single named strain sometimes resolving into distinct genetic clusters, an outcome consistent with the same name being applied by different growers to unrelated plants.[8] Because the crop has sat outside the variety-registration systems that certify other horticultural plants, a buyer has had no independent authority to appeal to: the label is the only claim, and nothing tests it.[8]
Chemical data point the same way. A survey of tens of thousands of commercial samples found the great majority to be THC-dominant whatever the "sativa", "indica" or "hybrid" label they carried, and resolved only a few recurring terpene profiles that likewise crossed the label boundaries.[10] The authors of these studies conclude that a commercial strain name is an unreliable guide to either the genetics or the chemistry of the plant in the packet.[8][10]
Chemovar and chemotype
A cultivar is a breeding category; a chemovar, or chemotype, is a chemical one. Two plants of the same cultivar can express different amounts of the same compounds depending on how they are grown, so chemical grouping cuts across breeding identity rather than tracking it.[11][12] Because both the effects and the legal status of a Cannabis plant follow its chemistry, the chemical grouping is often the more useful of the two, and analytical laboratories increasingly report a chemovar profile in place of a strain name.[11]
The established chemical scheme sorts plants by the ratio of the two major cannabinoids. Type I is dominated by tetrahydrocannabinol (THC), Type III by cannabidiol (CBD), and Type II carries both in comparable amounts; further classes cover plants dominated by cannabigerol (Type IV) or almost free of cannabinoids (Type V).[3] The THC-to-CBD balance is largely set by a single genetic locus at which codominant alleles direct the biosynthetic enzymes toward one cannabinoid or the other, so a plant's chemotype is substantially inherited and can be fixed by breeding; it is this predictability that lets regulators draw the boundary between hemp and drug Cannabis at a fixed THC percentage.[13][3]
Terpene composition adds a second chemical axis. Profiling of commercial material resolves a small number of recurring terpene groupings, led by compounds such as myrcene, limonene, caryophyllene and terpinolene, and these groupings cut across the cannabinoid types and across the names the material is sold under.[10] The proposal that terpenes shape the effect of the cannabinoids alongside which they occur, sometimes called an entourage effect, is one reason chemovar description has moved toward reporting the full cannabinoid and terpene profile rather than THC content alone.[14][11] Because growing conditions move these profiles, a chemovar describes a plant as measured rather than a fixed property of its lineage; that dependence of expressed chemistry on environment is an instance of phenotypic plasticity, and it is one reason a single cultivar cannot be assumed to deliver one chemotype across sites and seasons.[11]
Sativa and indica as cultivar categories
The commonest folk classification of drug Cannabis splits it into "sativa", "indica" and "hybrid" types, a vocabulary that predates and largely ignores the formal categories above. In trade usage the labels are meant to signal both a plant's build, tall and narrow-leafletted against short and broad-leafletted, and the character of its effect, with "sativa" sold as stimulating and "indica" as sedating.[4]
The link between the two has not held up. The physician and cannabis researcher Ethan Russo has argued that a plant's height, branching and leaf shape give no reliable guide to its chemistry, and that only assay of the actual cannabinoids and terpenes can establish what a plant will do.[15] Genomic work points the same way: generations of interbreeding have mixed the ancestries the labels once tracked, leaving "sativa" and "indica" as poor predictors of either genome-wide ancestry or chemical output.[16][9] The morphological contrast the terms capture is real, and is treated more precisely as the narrow-leaflet and broad-leaflet drug biotypes in Cannabis taxonomy and Cannabis indica; as cultivar categories, though, the folk labels carry little of the distinctness they seem to promise, which is why formal treatments set them aside in favour of chemotype and documented lineage.
From landrace to cultivar: breeding and stabilisation
Cultivars are drawn out of landraces by degrees. The oldest method is mass selection, in which a grower saves seed from the plants that best show a wanted trait and discards the rest; repeated over seasons it shifts a population without ever making it uniform, and it is the process by which farmers turned wild Cannabis into the regional landraces that later breeding drew on.[7][17] Formal cultivar breeding tightens selection further and pairs it with control over pollination.
Uniformity is reached by cutting genetic variability down and then holding it fixed. Repeated self-pollination or crossing between close relatives yields inbred lines that breed true; backcrossing moves a single wanted trait from one line into an established one by crossing back to the recurrent parent over several generations while keeping the rest of that parent's makeup.[7] Crossing two distinct inbred lines gives a first-generation hybrid population that is uniform and often more vigorous than either parent, an expression of hybrid vigour; that uniformity lasts only for the one generation, so such a cultivar is reproduced by remaking the cross rather than by saving its seed.[7][3]
Two features of Cannabis shape how its cultivars are held. Because the plant is normally dioecious, a seed crop involves two parents and some variability, whereas fibre and grain hemp breeders select monoecious lines so that a crop carries one sex expression and ripens evenly.[3][17] Breeders also work the plant's expression of sex to keep drug-type lines uniform, treating female plants so that they shed pollen and their seed yields only female offspring, and they select day-neutral autoflowering plants, a recessive character carried into cultivated stock from ruderal populations, to make flowering independent of daylength.[7]
How a cultivar is propagated then decides how faithfully it persists. A clone, taken as a cutting from a single mother plant, carries that plant's genotype unchanged and so reproduces a drug-type cultivar exactly, which is why most named drug-type Cannabis is kept clonally; the cost is that clonal stock accumulates viruses and other pathogens over successive passages and must be maintained as living plants rather than stored as seed.[7] A seed-propagated cultivar stores and ships easily and sheds its pathogens with each generation, but it only holds its type if it is a fixed inbred line or a remade first-generation cross; the open-pollinated seed of a hybrid segregates and loses uniformity within a single generation.[7][3]
Cannabis cultivar types
Registered and named Cannabis cultivars fall into a few broad purposes that track the plant's historical uses. Fibre hemp cultivars are selected for tall, little-branched stems with a high proportion of bast fibre and low cannabinoid content; grain cultivars for heavy, early-ripening seed; and dual-purpose cultivars for a workable compromise between the two.[3][17] A more recent class of hemp cultivar is selected for high CBD with THC held below the legal hemp threshold, a Type III chemotype grown for extraction rather than fibre or grain.[3] Long-standing European fibre and grain cultivars such as 'Carmagnola', 'Futura 75', 'Finola' and 'USO 31' are kept in national and regional variety catalogues, which is what gives them the documented, reproducible identity that most drug-type material lacks.
Drug-type cultivars are the products of the modern breeding set out above, selected for cannabinoid and terpene profile, yield and flowering time, then propagated mostly as clones. They are far more numerous than registered hemp cultivars but far less often documented, so the great majority exist as commercial names rather than as verified cultivars.[8] To bring some order to the range, Small's revision gathers cultivated Cannabis into a small set of cultivar Groups defined by use and chemistry, separating fibre and grain hemp from the narrow-leaflet and broad-leaflet drug plants; the scheme draws on genetic evidence for distinct hemp, drug and ruderal gene pools and is one attempt to give the informal market categories a footing in the cultivated-plant code.[3][18]
Distinctness, uniformity and stability
The formal test a plant group must pass to be registered as a cultivar is distinctness, uniformity and stability, usually shortened to DUS: it must be clearly distinguishable from existing cultivars, consistent in its selected characters within each generation, and unchanged across the generations of propagation used to maintain it.[1] A national authority examines a candidate against these criteria, often by growing it out beside reference cultivars, and where it passes, the breeder can be granted plant breeders' rights, a protection co-ordinated internationally through the International Union for the Protection of New Varieties of Plants that gives exclusive control over propagating and selling the variety for a set term. The DUS description filed at registration then doubles as the reference against which later plants claiming the cultivar's name can be checked.
Cannabis has largely sat outside this machinery, and unevenly. Fibre and grain hemp, treated as an ordinary agricultural crop, is registered and protected in the usual way and appears in national and regional variety lists. Drug-type Cannabis has until recently been shut out of most variety-protection systems by prohibition, and its clonal, undocumented breeding leaves few lines with the examination record registration requires.[8] The result is the identity problem already described: with neither registration nor a certifying authority, a named drug-type variety cannot be independently confirmed. Proposals to close the gap turn on genetic fingerprinting and chemical profiling, which would let a reference genotype and chemovar stand in for the DUS description that most drug-type cultivars have never been given.[8][9]
Conservation implications
The cultivar and the landrace mark two ends of a conservation problem. A cultivar is uniform, documented and, once registered, subject to intellectual property rights, which makes it easy to reproduce but narrow in the diversity it holds. A landrace carries the standing genetic diversity that adaptation draws on, but it exists only while farmers keep growing it and is lost when cultivation stops or when uniform cultivars crowd it out.[7][4]
For Cannabis the risk falls hardest on the drug-type landraces of southern and central Asia, whose distinctness is eroding as commercial cultivars spread and as prohibition disrupts traditional cultivation. A classification of these endangered populations argues for treating them under the botanical code as varieties worth conserving in their own right, apart from the cultivars bred out of them, and for capturing their diversity in ex situ collections before it goes.[4] The distinction between a landrace and a cultivar decides what a conservation programme is trying to keep: a living and variable population, or a fixed and repeatable line.[7]
See also
References
- ↑ 1.0 1.1 1.2 Brickell, C.D.; Alexander, C.; Cubey, J.J.; David, J.C.; Hoffman, M.H.A.; Leslie, A.C.; Malécot, V.; Jin, X., eds. (2016). International Code of Nomenclature for Cultivated Plants. Scripta Horticulturae. Vol. 18 (9th ed.). International Society for Horticultural Science.
- ↑ 2.0 2.1 2.2 Pollio, Antonino (2016). "The name of Cannabis: a short guide for nonbotanists". Cannabis and Cannabinoid Research. 1 (1): 234–238. doi:10.1089/can.2016.0027.
- ↑ 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 Small, Ernest (2015). "Evolution and classification of Cannabis sativa (marijuana, hemp) in relation to human utilization". The Botanical Review. 81 (3): 189–294. doi:10.1007/s12229-015-9157-3.
- ↑ 4.0 4.1 4.2 4.3 4.4 McPartland, John M.; Small, Ernest (2020). "A classification of endangered high-THC cannabis (Cannabis sativa subsp. indica) domesticates and their wild relatives". PhytoKeys. 144: 81–112. doi:10.3897/phytokeys.144.46700.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ↑ Zeven, A.C. (1998). "Landraces: a review of definitions and classifications". Euphytica. 104 (2): 127–139. doi:10.1023/A:1018683119237.
- ↑ Camacho Villa, T.C.; Maxted, N.; Scholten, M.; Ford-Lloyd, B. (2005). "Defining and identifying crop landraces". Plant Genetic Resources. 3 (3): 373–384. doi:10.1079/PGR200591.
- ↑ 7.00 7.01 7.02 7.03 7.04 7.05 7.06 7.07 7.08 7.09 Clarke, Robert C.; Merlin, Mark D. (2013). Cannabis: Evolution and Ethnobotany. University of California Press. ISBN 978-0-520-27048-0.
- ↑ 8.0 8.1 8.2 8.3 8.4 8.5 8.6 Schwabe, Anna L.; McGlaughlin, Mitchell E. (2019). "Genetic tools weed out misconceptions of strain reliability in Cannabis sativa: implications for a budding industry". Journal of Cannabis Research. 1 (1): 3. doi:10.1186/s42238-019-0001-1.
{{cite journal}}: CS1 maint: unflagged free DOI (link) - ↑ 9.0 9.1 9.2 Sawler, Jason; Stout, Jake M.; Gardner, Kyle M.; Hudson, Darryl; Vidmar, John; Butler, Laura; Page, Jonathan E.; Myles, Sean (2015). "The genetic structure of marijuana and hemp". PLOS ONE. 10 (8): e0133292. doi:10.1371/journal.pone.0133292.
{{cite journal}}: CS1 maint: article number as page number (link) CS1 maint: unflagged free DOI (link) - ↑ 10.0 10.1 10.2 Smith, Christiana J.; Vergara, Daniela; Keegan, Brian; Jikomes, Nick (2022). "The phytochemical diversity of commercial Cannabis in the United States". PLOS ONE. 17 (5): e0267498. doi:10.1371/journal.pone.0267498.
{{cite journal}}: CS1 maint: article number as page number (link) CS1 maint: unflagged free DOI (link) - ↑ 11.0 11.1 11.2 11.3 Hazekamp, Arno; Tejkalová, Katerina; Papadimitriou, Stelios (2016). "Cannabis: from cultivar to chemovar II – a metabolomics approach to cannabis classification". Cannabis and Cannabinoid Research. 1 (1): 202–215. doi:10.1089/can.2016.0017.
- ↑ Hazekamp, Arno; Fischedick, Justin T. (2012). "Cannabis – from cultivar to chemovar". Drug Testing and Analysis. 4 (7–8): 660–667. doi:10.1002/dta.407.
- ↑ de Meijer, E.P.M.; Bagatta, M.; Carboni, A.; Crucitti, P.; Moliterni, V.M.C.; Ranalli, P.; Mandolino, G. (2003). "The inheritance of chemical phenotype in Cannabis sativa L.". Genetics. 163 (1): 335–346. doi:10.1093/genetics/163.1.335.
- ↑ Russo, Ethan B. (2011). "Taming THC: potential cannabis synergy and phytocannabinoid-terpenoid entourage effects". British Journal of Pharmacology. 163 (7): 1344–1364. doi:10.1111/j.1476-5381.2011.01238.x.
- ↑ Piomelli, Daniele; Russo, Ethan B. (2016). "The Cannabis sativa versus Cannabis indica debate: an interview with Ethan Russo, MD". Cannabis and Cannabinoid Research. 1 (1): 44–46. doi:10.1089/can.2015.29003.ebr.
- ↑ Lynch, Ryan C.; Vergara, Daniela; Tittes, Silas; White, Kristin; Schwartz, C.J.; Gibbs, Matthew J.; Ruthenburg, Travis C.; deCesare, Kymron; Land, Donald P.; Kane, Nolan C. (2016). "Genomic and chemical diversity in Cannabis". Critical Reviews in Plant Sciences. 35 (5–6): 349–363. doi:10.1080/07352689.2016.1265363.
- ↑ 17.0 17.1 17.2 de Meijer, E.P.M.; van der Kamp, H.J.; van Eeuwijk, F.A. (1992). "Characterisation of Cannabis accessions with regard to cannabinoid content in relation to other plant characters". Euphytica. 62 (3): 187–200. doi:10.1007/BF00041753.
- ↑ Hillig, Karl W. (2005). "Genetic evidence for speciation in Cannabis (Cannabaceae)". Genetic Resources and Crop Evolution. 52 (2): 161–180. doi:10.1007/s10722-003-4452-y.