The number of species that compose the genus Cannabis is often debated. Some experts’ claim that the genus is composed of three distinct species designated Cannabis sativa, Cannabis indica and Cannabis ruderalis (1, 2). Others contend that the genus is composed of a single species—C. sativa L—which exhibits high degrees of variations and heterogeneity within different subpopulations.
According to most current scientific conventions, the plant is usually classified as a single species C. sativa. Historically, most of the groupings or subdivisions in the genus have been made on physical characteristics or uses of the plant. For example, hemp plants are described as tall and skinny do not produce cannabinoids or terpenes (3) are not psychoactive when consumed and are mainly used for the extraction of fiber and oil (4). Indica plants are typically short with broad leafs and generally are associated with sedative effects after consumption. Sativa plants are tall and skinny with narrow leafs, produce high levels of cannabinoids and terpenes and mediate psychoactive effects after consumption. (4). In addition, a large number of so-called Cannabis hybrids (crosses between the three Cannabis types) also exist.
Recent genomic and molecular biological analyses are beginning to provide new insights into the actual classification of the Cannabis genus. At present, there are six whole-genomes assemblies (two each) of three different strains of C. sativa. (4) These include Purple Kush (5, 6); Chemdawg (4) and LA confidential (4). In addition, there are two sativa transcriptomes (whole genome RNA analyses) , four mitochondrial genome assemblies (three sativa and one hemp) [4, 5, 7, 8], 6 chloroplast genome assemblies (5, 7, 9) and over 393 additional genomic resources that are being used to learn more about Cannabis classification (4).
Result of studies using the above mentioned genetic tools suggest that hemp is a distinct group and that two marijuana-type groups may also exist (5, 10, 11). To interpret their results, researchers suggested a naming convention based on leaf phenotypes: narrow-leaf drug type (NLDT) aka sativa, broad-leaf drug type (BLDT) aka indica and hemp (11). While 86% of plants classified as hemp fell into the hemp category, only 19% of popular sativa cultivar/brands fell into the NLDT category (sativa) and 27% of indica strains clustered within the BLDT (indica) group. Interestingly, 36% of so-called hybrid strains fell into the BLDT (indica) group and 62% were placed in the NLDT (sativa) category (4). Further, cultivars/brands that are most popularly reported as 100% sativa can be more closely related to be 100% indica (4).
Thanks to these genomic analyses it appears that the colloquial classifications given to individual Cannabis plants are not accurate. That said, it is important to note that the current genomic classification scheme is based on a small sample size and may not represent the actual genetic variation that exists in the Cannabis genus. To confirm or refute this possibility, more genomic analyses of existing Cannabis cultivars/brands must be performed before the genus can be accurately classified.
While current genomic studies may appear to be a purely academic exercise to some, accurate classification of Cannabis plants will be vitally important as Cannabis growers attempt to validate the identity, quality and properties of the cultivars/brands that they sell for medical or recreational purposes.
- Hillig, K. W., and Mahlberg, P. G. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae) Am. J. 2004; Bot. 91:966–975
- Hillig, K. W. Genetic evidence for speciation in Cannabis (Cannabaceae). Genet. Resources Crop Evol 2005; 52: 161–180
- Small, E, and Cronquist, A. A practical and natural taxonomy for Cannabis. Taxon. 1976; 25:405–435
- Vergara D, Baker, H, Clancy K, Keepers KG, Mendieta JP, Pauli CS, Tittes SB, White KH, Kane,NC Genetic and Genomic Tools for Cannabis sativa, Critical Reviews in Plant Sciences, 2016; 35:5-6, 364-377, DOI:10.1080/07352689.2016.1267496
- van Bakel,H., Stout, J. M., Cote, A. G., Tallon, C. M., Sharpe, A. G., Hughes, T. R., and Page, J. E. The draft genome and transcriptome of Cannabis sativa. Genome Biol. 2011; 12:1241–1250
- Li, R., Zhu, H., Ruan, J., Qian, W., Fang, X., Shi, Z., Li, Y., Li, S., Shan, G., and Kristiansen, K. De novo assembly of human genomes with massively parallel short read sequencing. Genome Res. 2010; 20: 265–272
- Vergara, D.,White, K. H., Keepers, K. G., and Kane, N. C. The complete chloroplast genomes of Cannabis sativa and Humulus lupulus. Mitochondrial DNA Part A 2015; 27: 3793–3794
- White, K. H., Vergara, D., Keepers, K. G., and Kane, N. C. The complete mitochondrial genome for Cannabis sativa. Mitochondrial DNA Part B 2016; 1: 715–716
- Oh, H., Seo, B., Lee, S., Ahn, D.-H., Jo, E., Park, J.-K., and Min,G.-S. Two complete chloroplast genome sequences of Cannabis sativa varieties. Mitochondrial DNA Part A. 2015; 27:2835–2837
- Sawler, J., Stout, J. M., Gardner, K. M., Hudson, D., Vidmar, J., Butler, L., Page, J. E., and Myles, S. The genetic structure of marijuana and hemp. PloS One 2015; 10: e0133292
- Lynch, R. C., Vergara, D., Tittes, S., White, K., Schwartz, C. J., Gibbs, M. J., Ruthenburg, T. C., Land, D. P., and Kane, N.C. Genomic and Chemical Diversity in Cannabis. Crit. Rev. Plant Sci. 2016: 35: 349–363