Cannabis
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, 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, cannabigerol, and cannabinol.
Etymology
Cannabis is a Scythian word. The ancient Greeks learned of the use of cannabis by observing Scythian funerals, during which cannabis was consumed. In Akkadian, cannabis was known as qunubu. It has been claimed by a few scholars that he word was adopted in to the Hebrew language as qaneh bosem, however there is little real backing for this view, and other plants have been proposed being named that.Description
Cannabis is an annual, dioecious, flowering herb. The leaves are palmately compound or digitate, with serrate leaflets. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf, 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 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 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, with the possible exception of C. sativa subsp. sativa var. spontanea, which is commonly described as "auto-flowering" and may be day-neutral.Cannabis is predominantly dioecious, 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 Erya dictionary defined xi 枲 "male Cannabis" and fu 莩 "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. Subdioecy 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 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, but sativa strains often produce monoecious individuals, which is possibly as a result of inbreeding.
Sex determination
Cannabis has been described as having one of the most complicated mechanisms of sex determination among the dioecious plants. Many models have been proposed to explain sex determination in Cannabis.Genetic sex determinitaion
Based on studies of sex reversal in hemp, it was first reported by K. Hirata in 1924 that an XY sex-determination system is present. At the time, the XY system was the only known system of sex determination. The X:A system was first described in Drosophila spp in 1925. 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 then, many different types of sex determination systems have been discovered, particularly in plants. Dioecy is relatively uncommon in the plant kingdom, and a very low percentage of dioecious plant species have been determined to use the XY system. In most cases where the XY system is found it is believed to have evolved recently and independently.
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".
The question of whether heteromorphic sex chromosomes are indeed present is most conveniently answered if such chromosomes were clearly visible in a karyotype. Cannabis was one of the first plant species to be karyotyped; however, this was in a period when karyotype preparation was primitive by modern standards. Heteromorphic sex chromosomes were reported to occur in staminate individuals of dioecious "Kentucky" hemp, but were not found in pistillate individuals of the same variety. Dioecious "Kentucky" hemp was assumed to use an XY mechanism. Heterosomes were not observed in analyzed individuals of monoecious "Kentucky" hemp, nor in an unidentified German cultivar. These varieties were assumed to have sex chromosome composition XX. 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 to isolate several genetic marker sequences that they name Male-Associated DNA in Cannabis, 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,
A polymerase chain reaction-based method for the detection of female-associated DNA polymorphisms by genotyping has been developed.
Environmental sex determination
Environmental sex determination is known to occur in a variety of species. Many researchers have suggested that sex in Cannabis is determined or strongly influenced by environmental factors. Experiments with plant hormone treatment has revealed that treatment with auxin and ethylene have feminizing effects while treat with cytokinins and gibberellins have masculinizing effects.Inducing sex-reversal of Cannabis is agriculturally useful because it allows hybridizing plants of the same genetic sex, producing seeds that are genetically single-sexed, which is in turn useful in the cannabinoid-focused sectors as they use female flowers as raw material. Many sex-reversal agents bear no resemblance to plant hormones and work through unknown mechanisms. For example, masculinization is most commonly induced with a variety of silver compounds, including silver thiosulfate, silver nitrate, and colloidal silver. Other masculinization compounds include aminoethoxyvinylglycine and cobalt chloride. Practical feminizing compounds include ethephon.
Induced sex-reversal does not remove all effects of genetic sex. Induced sex-reversal produces defects such as decreased pollen viability and germinability. Still, enough viable pollens are produced through this method for it to be useful.
Chemistry
Cannabis plants produce a large number of chemicals as part of their defense against herbivory. One group of these is called cannabinoids, which induce mental and physical effects when consumed.Cannabinoids, terpenes, terpenoids, and other compounds are secreted by glandular trichomes that occur most abundantly on the floral calyxes and bracts of female plants.