Cannabis strains are either pure or Hybrid varieties of Cannabis, typically of C. Sativa and C. Indica. Varieties are developed to intensify specific characteristics of the plant, or to differentiate the strain for the purposes of marketing it more effectively as a drug. Variety names are typically chosen by their growers, and often reflect properties of the plant such as taste, color, smell, or the origin of the variety. Cannabis strains commonly refer to those varieties with recreational and medicinal use. These varieties have been cultivated to contain a high percentage of cannabinoids. Several varieties of Cannabis, known as Hemp, have a very low Cannabinoid content, and are instead grown for their fiber and seed.
Types of varieties
Clone-only variety – The grower may distribute genetically identical clones of the plant. A clone is the only way to propagate a plant while retaining its exact genetic makeup. Nevertheless, the conditions under which the plant is grown will still greatly affect the final product.
Stable seed variety – Creating a genetically stable variety involves selectively choosing male and female cannabis plants and breeding them over the course of multiple generations. The final generation's seeds reliably grow into plants that exhibit the desired characteristics, though some genetic variation will still occur.
Unstable seed varieties – Unstable varieties are produced without numerous generations of breeding. Although they can be produced quickly, plants grown from these seeds may have widely varying characteristics. Commercial seed retailers generally do not distribute unstable seed varieties, though some disreputable shops might. Amateur and third-party growers may, whether knowingly or not, produce unstable derivatives from well known varieties and misleadingly call them by their true variety name.
Wild varieties or landraces – Some varieties, such as Colombian and Thai, refer to cannabis plants found growing wild in certain regions. Typically, these plants are used as bases for the production of more specialized varieties, such as G-13 or Hash.
Major variety types
The two species of the Cannabis genus that are most commonly grown are Cannabis indica and Cannabis sativa. A third species, Cannabis ruderalis is very short and produces only trace amounts of tetrahydrocannabinol (THC), and thus is not commonly grown for industrial, recreational or medicinal use. However, because Cannabis ruderalis flowers independently of the photoperiod and according to age, it has been used to breed autoflowering strains.
Pure sativas are relatively tall (reaching as high as 4.5 meters), with long internodes and branches, and large, narrow-bladed leaves. Pure indica varieties are shorter and bushier, have wider leaflets. They are often favored by indoor growers for their size. Sativas bloom later than indicas, often taking a month or two longer to mature. The subjective effects of sativas and indicas are said to differ, but the ratio of tetrahydrocannabinol (THC) to cannabidiol (CBD) in most named drug varieties of both types is similar (averaging about 200:1). Unlike most commercially developed strains, indica landraces exhibit plants with varying THC/CBD ratios. Avidekel, a medical marijuana strain developed in Israel, has a very low content of THC but a high content of CBD, limiting its recreational value but maximizing medical effect.
In addition to pure indica, sativa, and ruderalis varieties, hybrid varieties with varying ratios of these three types are common. For example, the White Widow hybrid containing about 60% indica and 40% sativa ancestry. These hybrid varieties exhibit traits from both parental types. There are also commercial crossbred hybrids which contain a mix of both ruderalis, indica and/or sativa genes, and are usually autoflowering varieties. "Lowryder" was an early an auto-flowering hybrid that retained the flowering behavior of ruderalis plants, while also producing appreciable amounts of THC and CBD. Autoflowering cannabis varieties have the advantage of being discreet due to their small stature. They also require shorter growing periods, as well as having the additional advantage that they do not rely on a change in the photoperiod to determine when to flower.
In legal markets, such as in Amsterdam, competition puts pressure on breeders to create increasingly attractive varieties to maintain market share. Breeders give their strains distinct and memorable names in order to help differentiate them from their competitors' strains, although they may in fact be very similar.
Popular strains are incorporated into new hybrids, which often bear a similar name to their parent. This phenomenon has occurred with Haze and Sour varieties, amongst others.
Black-market cannabis dealers sometimes falsely advertise their products as being of a certain strain to capitalise on that strains success or reputation.
Breeding new varieties
Breeding requires pollinating a female cannabis plant with male pollen. Although this occurs spontaneously and ubiquitously in nature, the intentional creation of new varieties typically involves selective breeding in a controlled environment.
When cannabis is cultivated for its psychoactive or medicinal properties, male plants will often be separated from females. This prevents the fertilization of the female plants, either to facilitate sinsemilla flowering or to provide more control over which male is chosen. Pollen produced by the male is caught and stored until it is needed.
When a male plant of one strain pollenates a female of another strain, the seeds will be F1 hybrids of the male and female. These offspring will not be identical to their parents. Instead, they will have characteristics of both parents. Repeated breeding results in certain characteristics appearing with greater regularity.
A common technique to stabilize a cannabis variety is called "cubing". A breeder seeking specific traits in the hybrid offspring (for example, greater resin production or tighter node spacing) will breed hybrid plants most exemplifying these characteristics with a parent plant. The same traits are sought in the new inbred offspring, which are then again bred with the original parent plant. This process is called cubing because it usually repeated across three, or possibly more generations before the variety's genetics are acceptably stable.