Cannabis () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species being recognized: Cannabis sativa, C. indica, and C. ruderalis. Alternatively, C. ruderalis may be included within C. sativa, or all three may be treated as subspecies of C. sativa, or C. sativa may be accepted as a single undivided species.
The plant is also known as hemp, although this term is usually used to refer only to varieties cultivated for non-drug use. Hemp has long been used for fibre, seeds and their oils, leaves for use as vegetables, and juice. Industrial hemp textile products are made from cannabis plants selected to produce an abundance of fibre.
Cannabis also has a long history of being used for medicinal purposes, and as a recreational drug known by several slang terms, such as marijuana, pot or weed. Various cannabis strains have been bred, often selectively to produce high or low levels of tetrahydrocannabinol (THC), a cannabinoid and the plant's principal psychoactive constituent. Compounds such as hashish and hash oil are extracted from the plant. More recently, there has been interest in other cannabinoids like cannabidiol (CBD), cannabigerol (CBG), and cannabinol (CBN).
Etymology
Cannabis is a Scythian word. The ancient Greeks learned of the use of cannabis by observing Scythian funerals, during which cannabis was consumed. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf (usually seven or nine), depending on variety and growing conditions. At the top of a flowering plant, this number again diminishes to a single leaflet per leaf. The lower leaf pairs usually occur in an opposite leaf arrangement and the upper leaf pairs in an alternate arrangement on the main stem of a mature plant.
The leaves have a peculiar and diagnostic venation pattern (which varies slightly among varieties) that allows for easy identification of Cannabis leaves from unrelated species with similar leaves. As is common in serrated leaves, each serration has a central vein extending to its tip, but in Cannabis this originates from lower down the central vein of the leaflet, typically opposite to the position of the second notch down. This means that on its way from the midrib of the leaflet to the point of the serration, the vein serving the tip of the serration passes close by the intervening notch. Sometimes the vein will pass tangentially to the notch, but often will pass by at a small distance; when the latter happens a spur vein (or occasionally two) branches off and joins the leaf margin at the deepest point of the notch. Tiny samples of Cannabis also can be identified with precision by microscopic examination of leaf cells and similar features, requiring special equipment and expertise.
Reproduction
All known strains of Cannabis are wind-pollinated and the fruit is an achene. Most strains of Cannabis are short day plants, having imperfect flowers, with staminate "male" and pistillate "female" flowers occurring on separate plants. "At a very early period the Chinese recognized the Cannabis plant as dioecious", and the (c. 3rd century BCE) Erya dictionary defined xi 枲 "male Cannabis" and fu 莩 (or ju 苴) "female Cannabis". Male flowers are normally borne on loose panicles, and female flowers are borne on racemes.
Many monoecious varieties have also been described, in which individual plants bear both male and female flowers. (Although monoecious plants are often referred to as "hermaphrodites", true hermaphrodites – which are less common in Cannabis – bear staminate and pistillate structures together on individual flowers, whereas monoecious plants bear male and female flowers at different locations on the same plant.) Subdioecy (the occurrence of monoecious individuals and dioecious individuals within the same population) is widespread. Many populations have been described as sexually labile.
As a result of intensive selection in cultivation, Cannabis exhibits many sexual phenotypes that can be described in terms of the ratio of female to male flowers occurring in the individual, or typical in the cultivar. Dioecious varieties are preferred for drug production, where the fruits (produced by female flowers) are used. Dioecious varieties are also preferred for textile fiber production, whereas monoecious varieties are preferred for pulp and paper production. It has been suggested that the presence of monoecy can be used to differentiate licit crops of monoecious hemp from illicit drug crops, Soon thereafter, Schaffner disputed Hirata's interpretation, and published results from his own studies of sex reversal in hemp, concluding that an X:A system was in use and that furthermore sex was strongly influenced by environmental conditions.
Since the 1920s, a number of sex determination models have been proposed for Cannabis. Ainsworth describes sex determination in the genus as using "an X/autosome dosage type". According to other researchers, no modern karyotype of Cannabis had been published as of 1996. Proponents of the XY system state that Y chromosome is slightly larger than the X, but difficult to differentiate cytologically.
More recently, Sakamoto and various co-authors have used random amplification of polymorphic DNA (RAPD) to isolate several genetic marker sequences that they name Male-Associated DNA in Cannabis (MADC), and which they interpret as indirect evidence of a male chromosome. Several other research groups have reported identification of male-associated markers using RAPD and amplified fragment length polymorphism. Ainsworth commented on these findings, stating,