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.

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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.

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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?).

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Second, Mary Jane has loose morals. She sleeps around, or, in more scientific terms, cannabis is promiscuous. Most marijuana lineages are able to produce viable offspring by crossing with other lineages.

Third, and then there is human intervention. We've been messing with marijuana for at least 10,000 years—hemp ropes that old have been found in Taiwanese tombs—and that further muddles the taxonomic waters. And we've been cultivating it for different purposes, including food and fiber, as well as for its medicinal and psychoactive effects, creating divergent lineages as we went.

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From its origins in South and Central Asia, the plant is now cultivated on every continent except Antarctica, and humans carried it around the world. Mexican marijuana, for example, didn't occur because a pot seed floated across the ocean, but because Spanish colonists in the 1530s brought seeds with them in a failed effort to establish a fiber hemp industry there. (The hemp experiment may have faltered, but feral marijuana got loose in Mexico nearly five centuries ago, and the rest is history.)

And not only have humans been cultivating and breeding marijuana for millennia, but because marijuana is so promiscuous, the genetic diversity created by human meddling is further increased by human-bred pot's ability to cross-breed with wild or feral strains. Give us a few years of commercial marijuana production in the Midwest, and that feral hemp ("ditch weed") left over from World War II may actually start to get people high.

The Taxonomic Debate

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The standard taxonomy, dating back to Linnaeus, is that marijuana and hemp are a single species, C. sativa, with a number of variants. But in the 19th century, French naturalist Jen-Baptiste Lamarck argued that differences in morphology and chemistry demanded a second species, C. indica, that was shorter, less fibrous and more psychoactive. In the 20th century, U.S. botanist Richard Evans Schultes posited the existence of a third species, C. afghanica.

The standard taxonomy—cannabis is a single species—is favored, but the debate is still alive and grows more heated each time another scientist or researcher makes the argument for multiple species. Small wishes it would go away.

"The issue is exaggerated and tends to mislead people," he said. "I almost feel that it's better not to talk about it anymore."

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Yet neither the demands for more clarity nor the interest of researchers is going away. And scientists are shifting their quests from examinations of plant morphology to looking into molecular structure and genetics.

A decade ago, researchers at Indiana University examined the enzyme-encoding genotypes of 157 marijuana samples and, based on the proportions of CBD and THC levels, argued for two species, C. sativa and C. indica, with six subspecies. One of the researchers, Karl Hillig, later published a broader study suggesting a third species, C. ruderalis.

In 2013, that position got support from botanist Mark Merlin at the University of Hawaii and cannabis researcher Robert Clarke of the International Hemp Association in Amsterdam. In their magisterial work, "Cannabis: Evolution and Ethnobotany," they argued for the three-species position, but concluded there were not six, but seven, subspecies.

Still, the matter remains unresolved. At the same time Hillig and his team at Indiana were advancing the three-species thesis, other researchers were also looking at CBD/THC ratios, and they developed a single species position, but with five different lineages.

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And the work goes on. Canadian botanist Page and his colleagues have published a draft set of the DNA and RNA of a marijuana plant and compared that to the RNA of a hemp plant, finding "tantalizing differences" in the way cannabinoid-controlled genes are expressed. Another botanist, Nolan Kane of the University of Colorado, is working on a "genetic map" that will include complete gene sequencing of some 500 plants. That work could provide "unprecedented" insight into the relationships between the major cannabis lineages, Kane said.

It's not just a matter of semantics. Identifying and defining lineages is important because researchers need to know what they're working with. Most commercially available marijuana is not of a pure lineage, but is hybrid, and while that can make for fast-growing, super-stony smoke, it isn't that useful for scientists.

"Many taxonomic studies and genetic studies work with Cannabis hybrids, and generate inconclusive results," GW Pharma botanist John McPartland explained.

"In the marijuana world, we don't have varieties or registered cultivars—we have these things called strains," Page said, noting that these are informal classifications not associated with genotypes in the same way formal varieties or cultivars are. "You need to put a name on something to research it."

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C. sativa or c. sativa, c. indica, and c. ruderalis? Don't feel bad if you're not sure. Nobody else really is either.

Phillip Smith is editor of the AlterNet Drug Reporter and author of the Drug War Chronicle.