The Genus Cannabis: Taxonomy and Biochemistry

Marijuana and Hemp have placed a heavy burden on public policymakers.

Wednesday the 3rd of June, 2009

Many believe that by legalizing hemp they are legalizing marijuana. Yet in other countries, governments have accepted the distinction between the two types of Cannabis and, while continuing to penalize the growing of marijuana, have legalized the growing of industrial hemp.

Field Corn and Sweet Corn

Functional distinctions among varieties are commonly recognized. The untrained observer cannot tell the different varieties apart just by looking. Both belong to the genus Zea mays. When sweet corn is planted too near field corn, the resulting cross-pollination reduces the quality of the sweet corn. Companies that grow huge acreages of sweet corn go to great lengths to ensure that an adequate distance separates their fields from corn destined for the grain elevator, or they grow the different varieties at different times. Either way, pollen carrying the dominant gene for starch synthesis is kept clear of cornsilk borne on plants of the recessive (sweet) variety. Commercial producers of planting seed of either variety are very careful to preserve the genetic integrity of their lines from contamination by other varieties. Their genetic resources are assemblages of optimized characteristics—yield, disease resistance, maturity—created through substantial research investment. Breeders of these crops rigorously ensure that their breeding stocks do not become contaminated by the other type, as this would result in a serious decline in the quality factors each tries to enhance. This botanical distinction is reflected even in the academic disciplines that deal with corn. Go to a mid-western land grant university’s agriculture college and ask to speak to a plant breeder about sweet corn and you will be sent to the horticulture department; for field corn you will be directed to the agronomy department.

Opium Poppy and Breadseed Poppy

A similar situation exists with respect to poppies, the popular garden flower of which there are dozens of variants. Recently the U. S. Drug Enforcement Administration has been cracking down on one specific poppy variety grown in backyards for many years, because it says that opium can be extracted from it. Yet the DEA still considers it legal for gardeners to continue to cultivate the many other varieties of Papaver somniferum, even though these are not botanically distinct from the poppy variety that has been outlawed. In similar fashion, the so-called “breadseed poppy” is also a member of the same species, yet the Controlled Substances Act specifically sets aside the poppy seed because of the culinary market. With corn and poppies, we can understand the distinctions among varieties and strains. Until recently, as we shall see, the U. S. federal government also recognized the distinctions among the different varieties of Cannabis.

The Genus Cannabis: Taxonomy and Biochemistry

Scientists who were the first to study the genus Cannabis clearly discerned different species. The father of plant taxonomy, Linnaeus, officially designated the Cannabis genus in 1753 when he founded the binomial system of botanical nomenclature. Linnaeus added the “sativa” appellation (literally, “sown” or “cultivated,” i.e., used in agriculture), indicating the utilitarian nature of the plant. Since his time numerous attempts have been made for a coherent taxonomy of Cannabis. Species designations have come and gone.

In 1889, botanist and plant explorer George Watt wrote about the distinction between types of Cannabis: “A few plants such as the potato, tomato, poppy and hemp seem to have the power of growing with equal luxuriance under almost any climatic condition, changing or modifying some important function as if to adapt themselves to the altered circumstance. As remarked, hemp is perhaps the most notable example of this; hence, it produces a valuable fibre in Europe, while showing little or no tendency to produce the narcotic principle which in Asia constitutes its chief value.”

Dr. Andrew Wright, an agronomist with the University of Wisconsin’s Agriculture Experiment Station and steward of the Wisconsin hemp industry during the first half of the twentieth century, wrote in 1918, “There are three fairly distinct types of hemp: that grown for fibre, that for birdseed and oil, and that for drugs.”

Although these early analysts discerned clear differences among hemp types, taxonomists have had a difficult problem in deciding how to reflect those differences. The key Cannabis species problem derives from the fact that there is no convenient species barrier between the varying types that would allow us to draw a clear line between them. In taxonomy, often the delineating line between species is that they cannot cross-breed. But disparate types of Cannabis can indeed produce fertile offspring, not sexually dysfunctional “mules.” Consequently, a debate has raged within botanical circles as to how many species the genus contains.
At this time botanists generally recognize a unique family of plants they call “Cannabaceae,” under which are classified the genus Cannabis and its closest botanical relative, Humulus, which contains the beer flavouring, hops. The prevailing opinion currently recognizes three species: C. sativa, C. indica, and C. ruderalis. “Industrial” types fall exclusively within C. sativa, although all Cannabis plants contain stem fibre and can have multiple uses in primitive societies where they are indigenous. Recent analytical advances are leading many scientists to believe that a more accurate and satisfying way to differentiate the different forms of Cannabis would be by their biochemical composition.
Cannabis is the only plant genus in which can be found the unique class of molecules known as cannabinoids. Cannabis produces two major cannabinoids— THC (delta-9 tetrahydrocannabinol) and CBD (cannabidiol), and several other minor cannabinoid compounds. THC is responsible for the psychoactive effect. That was demonstrated conclusively in the 1960s. CBD, on the other hand, has recently been shown to block the effect of THC in the nervous system. Cannabis strains of the type used for industrial purposes have relatively high levels of CBD versus THC. Drug strains are high in THC and low to intermediate in CBD.
Smoking hemp, high in CBD and very low in THC, actually has the effect of preventing the marijuana high. Even when the amount of THC in a sample is as high as 2 percent, the psychological high is blocked by as little as 2 percent CBD. Cannabis with THC below 1.0 percent and a CBD/THC ratio greater than one is therefore not capable of inducing a psychoactive effect. Hemp, it turns out, is not only not marijuana, it could be called “antimarijuana.” The balance of cannabinoids i s determined by the genetics of the plant. That it is a stable characteristic of a given genotype (i.e., the individual’s specific genetic complement) was demonstrated by Dr. Paul Mahlberg of Indiana University-Bloomington. In other words, plants do not capriciously alter their cannabinoid profile. Thus, using the chemo type approach, Cannabis variants can be classified on the basis of their THC-CBD balance.
This is accepted by a growing number of scientists. Gabriel Nahas, M.D., Ph.D., writes, “One should still distinguish two principal large groups of varieties of Cannabis sativa, the drug type and the fibre type. In addition to this classical distinction of these two groups, botanists generally accept description consisting of three chemical types: (a) The pure drug type, high THC content (2-6 percent) and lacking CBD [cannabidiol]; (b) The “intermediate type” (predominantly THC); (c) The fibre type (THC<0.25 percent).” Dr. Mahmoud El Sohly, Director of the National Institute on Drug Abuse Marijuana Project at the University of Mississippi-Oxford, which analyses Cannabis samples sent in by law enforcement agencies, explained to the author that his group is currently re-evaluating the data collected since the 1960s. They are taking a new approach that classifies any sample with less than 1.0 percent THC and a CBD to- THC ratio greater than one as “ditchweed,” in order to have a proper discrimination among the samples. This was never done for the data on which the claims of great potency increase are based, from pre-1983 samples.
Interestingly, this same threshold— THC less than 1 percent and the ratio of CBD to THC greater than one —is a prescription for industrial hemp.
Current hemp varieties grown in Canada and Europe are certified to have THC levels below 0.3 percent. The certification system originally developed in Europe to allow for the commercialization of industrial hemp considered the ratio of CBD to THC as well as the absolute percent THC. The original THC threshold was 0.8 percent. When varieties with lower levels of THC were developed by French breeders, the breeders were able to persuade the European Union to reduce the tolerance further, giving the French until recently a de facto monopoly of hemp seed varieties sold in the European Union. In the United States, Cannabis with any detectable trace of THC is illegal. CBD is not considered at all.

Exposing the Myths

Much of the rest of the world quickly and relatively easily moved beyond the debate about hemp and marijuana to focus on how best to reintroduce a crop that at one time was the world’s best selling fibre. The United States is still paralysed by the belief that industrial hemp is a drug crop. This belief has been nurtured by the dissemination of much misinformation. Hemp and Marijuana: Myths & Realities -David P. West, Ph.D. for the North American Industrial Hemp Council (NAIHC) http://www.naihc.org/

132: Dominant or Recessive | 2009 June 3rd | Cannabis HEMP, MEDICINE | Articles, HEMP