Cannabis Systematics at the Levels of Family, Genus, and Species

Abstract

New concepts are reviewed in Cannabis systematics, including phylogenetics and nomenclature. The family Cannabaceae now includes Cannabis, Humulus, and eight genera formerly in the Celtidaceae. Grouping Cannabis, Humulus, and Celtis actually goes back 250 years. Print fossil of the extinct genus Dorofeevia (=Humularia) reveals that Cannabis lost a sibling perhaps 20 million years ago (mya). Cannabis print fossils are rare (n=3 worldwide), making it difficult to determine when and where she evolved. A molecular clock analysis with chloroplast DNA (cpDNA) suggests Cannabis and Humulus diverged 27.8 mya. Microfossil (fossil pollen) data point to a center of origin in the northeastern Tibetan Plateau. Fossil pollen indicates that Cannabis dispersed to Europe by 1.8-1.2 mya. Mapping pollen distribution over time suggests that European Cannabis went through repeated genetic bottlenecks, when the population shrank during range contractions. Genetic drift in this population likely initiated allopatric differences between European Cannabis sativa (cannabidiol [CBD]>Δ⁹-tetrahydrocannabinol [THC]) and Asian Cannabis indica (THC>CBD). DNA barcode analysis supports the separation of these taxa at a subspecies level, and recognizing the formal nomenclature of C. sativa subsp. sativa and C. sativa subsp. indica. Herbarium specimens reveal that field botanists during the 18th-20th centuries applied these names to their collections rather capriciously. This may have skewed taxonomic determinations by Vavilov and Schultes, ultimately giving rise to today's vernacular taxonomy of "Sativa" and "Indica," which totally misaligns with formal C. sativa and C. indica. Ubiquitous interbreeding and hybridization of "Sativa" and "Indica" has rendered their distinctions almost meaningless.

Keywords: Cannabaceae; Cannabis sativa; barcode; center of origin; molecular clock; palynology.

FIG. 1.

Macrofossils identified as Cannabis (not to scale). (A, B) Are from Friedrich, and (C) Is from Palamarev. (A, B) Reproduced from a publication whose copyright has expired; (C) Reproduced courtesy of Vladimir Bozukov, Bulgarian Academy of Sciences.

FIG. 2.

Phylogenetic tree used for calculating divergence dates.

FIG. 3.

Taxon names applied by field botanists. Locations of “C. sativa” labeled alphanumerically, s1, s2, and so on. Locations of “C. indica” labeled alphanumerically, i1, i2, and so on. Locations of other Cannabis taxa labeled alphanumerically, x1, x2, and so on. Base map shows the boundaries of 10 floristic regions (Takhtajan 1986). Map adapted from McPartland and Guy, which links alphanumerical sites with literature citations.

FIG. 4.

Cannabis vernacular taxonomy, image adapted from Anderson, courtesy of the Harvard University Herbaria and Botany Libraries.