Plant 297

Cannabis sativa L. (Cannabaceae)


For thousands of years an intricate cultural canvas has been woven by the complex interactions among cannabis and the peoples with which it has travelled. We are most familiar with cannabis as marijuana, the drug that helps people encounter their gods, escape their daily lives or, perhaps, heal their ailments. But cannabis is also hemp. Hemp sails and ropes linked outposts of empires, and hemp seed oil is both food and lubricant. In China, cannabis has been continuously cultivated, as both fibre and food, for at least 6,000 years, whence its cultivation and use spread globally.

The consensus that drug and fibre both come from the same species has only been reached after centuries of intense botanical discussion. Cannabis sativa is the sole member of the genus Cannabis, although two subspecies are recognized, both of which have wild and cultivated forms. In one subspecies, ssp. sativa, stems and fruits have been selected for fibre, food and oil production, while in the other subspecies, ssp. indica, flowers and leaves have been selected for drug production.

Cannabis is a tall, annual, wind-pollinated herb, with separate male and female plants. The hand-like leaves, with their narrow, serrated leaflets, are immediately recognizable. Strict legislation surrounding cannabis cultivation means living plants are rarely seen, although it occasionally pops up in rubbish dumps and in gardens, and the fleeting, sweetish odour of cannabis smoke is familiar on city streets.

While the Chinese domesticated cannabis for fibre, inhabitants of the Indian subcontinent focused on its drug properties. The psychoactive drug THC (tetrahydrocannabinol) is concentrated in minute glands that cover the flower buds, especially in female plants. Typically, THC content is below 0.3 per cent dry weight but may reach 20 per cent dry weight in some drug-producing cultivars.

Fibre-producing cannabis contains very little THC. The mechanical rather than transcendental properties attracted the Chinese and most early cannabis growers. In the age of sail, keeping a navy afloat meant having a constant supply of hemp for sails and rigging; 'our whole mercantile, as well as royal maritime power, depends on supplying ourselves with cordage' wrote Malachy Postlethwayt, an eighteenth-century trade expert. With a warship needing about 80 tons of hemp, equivalent to the output of 400 acres of land, hemp production competed with food production. Successive British governments were therefore exercised with the strategic problem of hemp procurement. Gradually, maritime uses became redundant as alternatives to hemp emerged.

Further reading

Clarke RC and Merlin MD 2013. Cannabis. Evolution and ethnobotany. University of California Press, Berkeley.

Jiang H-E et al. 2006. A new insight into Cannabis sativa (Cannabaceae) utilization from 2500-year-old Yanghai Tombs, Xinjiang, China. Journal of Ethnopharmacology 108: 414-422.

Small E 1975. On toadstool soup and legal species of marihuana. Plant Science Bulletin 21: 34-39.

Stephen Harris