Cannabis is a genus of annual flowering plants . It is dioecious, meaning that some plants have male flowers and others have female flowers. Some plants have both male and female flowers. It is wind pollinated. The leaves are palmate, meaning that they form leaflets which radiate from the base of the leaf. The leaflets are serrated . The plant is indigenous to Asia. Cannabis can be identified from similar plants by looking at some of its characteristics .
Cannabis plants have small hairs called trichomes. There are several different types of trichomes . The trichomes on female plants are particularly high in Δ-9-tetrahyocannabinol (THC) content. The purpose of the trichomes is not entirely clear, but may be, in part, to trap insects that would try to eat the plant.
Cannabis belongs to the family Cannabaceae . The family Cannabaceae is composed of flowering plants, and includes hops plants and a type of tree called hackberries, as well as cannabis. The main similarities among the members of this family typically include palmate leaves, dioecious flowers, and wind pollination.
Cannabis is often divided into 3 species—Cannabis sativa, Cannabis indica, and Cannabis ruderalis—but there is significant disagreement about this [4–6]. There are also some named varieties, for example Cannabis indica var. kafristanica, and Cannibis sativa var. spontanea . Each species can interbreed with the other species, leading to hybridization. One of the disagreements is whether this should be one species or different species. One definition of species is one in which a group of organisms can interbreed in nature. Using this definition, some consider cannabis a single species of C. sativa L. (Linnaeus) with subspecies sativa, indica and ruderalis [1, 7]. Others, disagree, arguing that the capacity for hybridization should not be the major determinant for some plants, but rather phytochemical composition, leading to the idea that they should be considered different species .
Cannabis sativa is the most commonly occurring subspecies in the West. It is a tall thin-leaved plant, which flowers under certain light conditions. Flowering is initiated when darkness exceeds 11 h per day . It can grow to 5–18 feet or more, and often has a few branches.
Cannabis indica is more broad-leaved than C. sativa. It is most commonly shorter and has more leaves and buds, giving it a more bushy appearance. The buds tend to be wider. It typically grows 2–4 feet tall, and is compactly branched.
Cannabis ruderalis may have originated from southern Russia. It contains very low THC, so is rarely grown by itself. It has the property of autoflowering: flowers appear as a result of plant age rather than light conditions. It is principally used in hybrids, to enable the hybrid to have the autoflowering property. The plants are smaller than C. sativa and have adapted to colder temperatures than C. sativa. It does not typically grow to be more than 2 feet tall and is unbranched .
It is important to note that there is ongoing hybridization, to create new strains and select desirable characteristics. One of the characteristics frequently chosen is THC content. Between 2000 and 2004, the average THC content of marijuana plants from the Netherlands rose from 8 % to 20 % . A larger multinational view also saw an increase over time, but not as strong as seen in the Netherlands .
While there is some concern with regard to the high THC content of modern hybrids, there is probably no added therapeutic effectiveness. In one study among medical marijuana users in the Netherlands, 3 different preparations of pharmaceutical-grade cultivated cannabis, which have been tested and verified for their components, were compared. The preparations contained 19 % THC, < 1 % cannabidiol (CBD); 12 % THC, < 1 % CBD; or 6 % THC, 7.5 % CBD. Patients were asked to rate 12 adjectives on a scale of 1 to 100, to describe the subjective experiences. They did not find significant differences, except that increased appetite was seen in both the 19 % and 12 % THC preparations (p = 0.03); the feelings of dejection and anxiety were both higher in the high THC group than in the low THC group (p = 0.006 and p = 0.004, respectively) . Another study looked at patients with HIV/AIDS, and compared C. sativa, C. indica, and 2 hybrids. They found significant differences in only in two areas. Cannabis indica had increased energy (mean difference of 1.53) and appetite (mean difference of 1.79) compared with C. sativa and a smaller difference to other marijuana on a visual analogue scale of 1 to 10 .
In an Australian study looking at various constituents of marijuana, the content of total THC varied between 1 % and 40 % in samples tested. CBD varied between 0 % and 6 % .