Hemp (Cannabis sativa L.) fiber can be used for biocomposites, textile, and many other applications.
Sowing density and harvest time are considered important crop management factors influencing fibre quantity and quality in 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. 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).
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.
1. Source: Hemp and Marijuana: Myths & Realities -David P. West, Ph.D. for the North American Industrial Hemp Council (NAIHC) http://www.naihc.org/