Cannabis sativa vs cannabis indica

Is all marijuana from a singles species, cannabis sativa? Or are there three distinct species: cannabis sativa, cannabis indica, and cannabis ruderalis?

Weed connoisseurs have long grappled with the issue as, intent on their pursuit of a more perfect buzz, they have now built up a couple of generations' worth of experience with plant breeding, hybridization and cross-pollination. That was pretty much all in the pursuit of getting high, but in the past couple of decades, interest has also turned to cannabinoids other than THC, such as cannabidiol (CBD), with all its apparent medicinal properties, not to mention increased interest in industrial hemp.

Now, as marijuana increasingly moves out from the shadows and into a regulatory - as opposed to prohibitionist - environment, the question becomes ever more pressing, and not just for stoners. With the commercialization of cannabis already well underway in California, Colorado, Washington and other states, and its medicalization advancing worldwide, governments and the scientific research community are facing rising demands for taxonomic clarity.

Canadian government botanist Ernest Small's research on the natural range of THC concentrations helped the Canadian set standards that allowed the classification of plants with less than 0.3 percent THC as hemp, not marijuana, creating groups of plants with stable characteristics, and registering them as formal hemp cultivars. Now farmers in those countries can grow hemp without fear of running afoul of drug laws.

Creating that chemical threshold was a pragmatic and useful response, but a settled taxonomy would allow researchers, regulators, growers and consumers to use a clear and common language to describe the plant.

Talking about cannabis taxonomy "is really talking about the ability of countries to rationally regulate important drugs and products," Small explained to Nature. But his research allowed governments to skirt the taxonomy question, and that could be a good thing.

"It's complicated taxonomically because of its intimate relationship with humans over a long period of time," explained University of British Columbia botanist Jonathan Page. And that's not the only reason.

First, pot is old. Cannabis diverged from the hops plant, humulus, around 28 million years ago, according to a genetic analysis by researchers at London-based GW Pharmaceuticals, the manufacturers of Sativex, a whole plant cannabis medicine. That means it's had millions of years to evolve, with geographical and environmental diversity playing an as yet unclear role in the development of distinct lineages (or are they species?).

The differences between the two species are evident to the naked eye. Sativas typically are tall and lanky, with long narrow leaves, while indicas are shorter, stouter, bushier, and have thicker, stubbier leaves. That, says Krymon deCesare, chief research director at Steep Hill Halent Lab in Oakland, is because the two cannabis species developed in different environments.