Cannabis Systematics at the Levels of Family, Genus, and Species
John M. McPartland
Cannabis and Cannabinoid Research, 2018, Volume 3.1, 203-
Doi : 10.1089/can.2018.0039
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] >D9-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; center of origin; barcode; molecular clock; palynology
Taxonomy includes classification (the identification and categorization of organisms) and nomenclature
(the naming and describing of organisms). Taxonomy, in the light of evolution, becomes systematics: the evolutional relationships among living things. Classification, in the light of evolution, becomes phylogenetics: the genealogical study of relationships among individuals and groups in a nested hierarchy.
This review of Cannabis systematics will consist of four sections: (1) the family Cannabaceae with the recent addition of former Celtidaceae; (2) the genus Cannabis, and when and where she evolved; (3) the species Cannabis sativa, including two subspecies: C. sativa subsp. sativa and C. sativa subsp. indica; (4). the vernacular taxonomy of ‘‘Sativa’’ and ‘‘Indica.’’
The Family Cannabaceae
The family Cannabaceae currently consists of Cannabis and Humulus, plus eight genera formerly in the Celtidaceae: Celtis, Pteroceltis, Aphananthe, Chaetachme, Gironniera, Lozanella, Trema, and Parasponia.1 Some botanists combine Parasponia and Trema, but Parasponia species uniquely form nitrogen-fixing nodules in symbiosis with rhizobial bacteria. This trait is shared only by legumes. In contrast, other Cannabaceae form a symbiosis with arbuscular mycorrhizal fungi, including Cannabis.2 Family Cannabaceae now includes about 170 species.
Cesalpino3 first elucidated taxonomic affinities between Cannabis and her sister genus Humulus in
1583. Before him, botanists classified Cannabis with phylogenetically unrelated plants based on leaf shape, human usage, and other totally artificial characters. Cesalpino was an Aristotelian essentialist; he reasoned that plants should be classified by the morphology of their most essential functions—reproduction (flowers and fruits), and nutrition (xylem and phloem). Schultes4 summarizes, ‘‘the earliest trend in taxonomic works was to include Cannabis in the Urticaceae; that in the last half of the last century [19th] and the early part of this century [20th], most authorities favoured the Moraceae; that the modern tendency appears to maintain the family Cannabaceae as separate from these.’’ Schultes is widely quoted or paraphrased, but he presented a simplified history of taxonomy.
Early taxonomists lumped together members of the Urticaceae, Moraceae, and Cannabaceae, and referred to these amalgamated entities by a variety of names. For example, Adanson5 lumped 11 genera in 1763: Cannabis, Humulus, Celtis, two Urticaceae genera, four Moraceae genera, and two unrelated genera. His accuracy (percentage of genera now placed in Cannabaceae, Urticaceae, or Moraceae) was 9 out of 11, or 82%. Some other early concepts are presented in Table 1.
Adanson5 was more accurate than Linnaeus,6 but Lamarck7 outdid them both—although only Adanson accurately combined Cannabis, Humulus, and Celtis. Lamarck7 first placed Cannabis and Humulus in Moraceae (although using French instead of Latin, as Figuiers), and de Jussieu8 first placed Cannabis and Humulus in Urticaceae (spelling it Urticae).
Several 18th century taxonomists followed Adanson and grouped Cannabis, Humulus, and Celtis,11–13 but Adanson’s concept lost recognition thereafter. Batsch9 first segregated Cannabis and Humulus into their own subfamily. Martynov10 elevated the pair to a family rank, and coined the name Cannabaceae. Subsequent botanists, unaware of Martynov, coined Cannabineae15 and Cannabinaceae.16 These incorrect spellings still appear in the literature. Others continued to place Cannabis into the Urticaceae or Moraceae.17,18
Not until the mid-20th century has Cannabaceae come into common usage.19