Cannabis - Taxonomy - Continuing Research

Continuing Research

Molecular analytical techniques developed in the late 20th century are being applied to questions of taxonomic classification. This has resulted in many reclassifications based on evolutionary systematics. Several studies of Random Amplified Polymorphic DNA (RAPD) and other types of genetic markers have been conducted on drug and fiber strains of Cannabis, primarily for plant breeding and forensic purposes. Dutch Cannabis researcher E.P.M. de Meijer and coworkers described some of their RAPD studies as showing an "extremely high" degree of genetic polymorphism between and within populations, suggesting a high degree of potential variation for selection, even in heavily selected hemp cultivars. They also commented that these analyses confirm the continuity of the Cannabis gene pool throughout the studied accessions, and provide further confirmation that the genus comprises a single species, although theirs was not a systematic study per se.

Karl W. Hillig, a graduate student in the laboratory of long-time Cannabis researcher Paul G. Mahlberg at Indiana University, conducted a systematic investigation of genetic, morphological, and chemotaxonomic variation among 157 Cannabis accessions of known geographic origin, including fiber, drug, and feral populations. In 2004, Hillig and Mahlberg published a chemotaxomic analysis of cannabinoid variation in their Cannabis germplasm collection. They used gas chromatography to determine cannabinoid content and to infer allele frequencies of the gene that controls CBD and THC production within the studied populations, and concluded that the patterns of cannabinoid variation support recognition of C. sativa and C. indica as separate species, but not C. ruderalis. The authors assigned fiber/seed landraces and feral populations from Europe, central Asia, and Asia Minor to C. sativa. Narrow-leaflet and wide-leaflet drug accessions, southern and eastern Asian hemp accessions, and feral Himalayan populations were assigned to C. indica. In 2005, Hillig published a genetic analysis of the same set of accessions (this paper was the first in the series, but was delayed in publication), and proposed a three-species classification, recognizing C. sativa, C. indica, and (tentatively) C. ruderalis. In his doctoral dissertation published the same year, Hillig stated that principal components analysis of phenotypic (morphological) traits failed to differentiate the putative species, but that canonical variates analysis resulted in a high degree of discrimination of the putative species and infraspecific taxa. Another paper in the series on chemotaxonomic variation in the terpenoid content of the essential oil of Cannabis revealed that several wide-leaflet drug strains in the collection had relatively high levels of certain sesquiterpene alcohols, including guaiol and isomers of eudesmol, that set them apart from the other putative taxa. Hillig concluded that the patterns of genetic, morphological, and chemotaxonomic variation support recognition of C. sativa and C. indica as separate species. He also concluded there is little support to treat C. ruderalis as a separate species from C. sativa at this time, but more research on wild and weedy populations is needed because they were underrepresented in their collection.

In September 2005, New Scientist reported that researchers at the Canberra Institute of Technology had identified a new type of Cannabis based on analysis of mitochondrial and chloroplast DNA. The New Scientist story, which was picked up by many news agencies and web sites, indicated that the research was to be published in the journal Forensic Science International.

Read more about this topic:  Cannabis, Taxonomy

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