Genetic Resources and Crop Evolution

, Volume 63, Issue 2, pp 349–359 | Cite as

Size matters: evolution of large drug-secreting resin glands in elite pharmaceutical strains of Cannabis sativa (marijuana)

  • Ernest SmallEmail author
  • Steve G. U. Naraine
Research Article


Most tetrahydrocannabinol (THC) of Cannabis sativa is located in the resin heads of capitate-stalked glandular trichomes. We found that after harvest the resin heads shrink in diameter in exponential decay fashion under ambient room conditions, losing about 15 % in the first month, rising to 24 % over the first year, 32 % by 50 years, and 34 % after a century. An equation accounting for the asymptotic curve descriptive of the progression of shrinkage was determined [original gland head diameter in microns = observed diameter divided by (0.5255 + 0.4745 multiplied by time in days to the power −0.1185)], so that if the age of a specimen is known, the original diameter of the gland heads in the fresh state can be extrapolated. This equation was employed to compare gland head size in samples of different ages. A sample of high-THC medical marijuana strains marketed under license possessed resin head diameters averaging 129 μm, while a sample of low-THC industrial hemp cultivars possessed gland head diameters averaging 80 μm. The mean volume of the resin heads of the narcotic strains was more than four times larger than that of the industrial hemp strains. This is the first documented report of a consistent morphological separator of elite narcotic strains and non-narcotic plants. Most recognized strains of marijuana were bred clandestinely and illicitly during the last half century. The occurrence of large resin gland heads in a sample of officially marketed pharmaceutical strains is an obvious correlate of selection for higher quantity of resin production.


Cannabinoids Cannabis sativa Glandular trichomes Hemp Marijuana THC 



We thank Nicholas Boileau, Brenda Brookes and Tanya Antle for technical assistance.


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Authors and Affiliations

  1. 1.Science and Technology BranchAgriculture and Agri-Food CanadaOttawaCanada
  2. 2.Department of Chemistry and BiologyRyerson UniversityTorontoCanada

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