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The leaves have a peculiar and diagnostic venation pattern that enables persons poorly familiar with the plant to distinguish a cannabis leaf from unrelated species that have confusingly similar leaves (see illustration). Within these two subspecies, Small and Cronquist described C. This taxonomic interpretation was embraced by Cannabis aficionados who commonly distinguish narrow-leafed "sativa" strains from wide-leafed "indica" strains.As is common in serrated leaves, each serration has a central vein extending to its tip. The authors hypothesized that the two subspecies diverged primarily as a result of human selection; C. sativa was presumably selected for traits that enhance fiber or seed production, whereas C. Molecular analytical techniques developed in the late 20th century are being applied to questions of taxonomic classification. de Meijer and coworkers described some of their RAPD studies as showing an "extremely high" degree of genetic polymorphism between and within populations, suggesting a high degree of potential variation for selection, even in heavily selected hemp cultivars. In his doctoral dissertation published the same year, Hillig stated that principal components analysis of phenotypic (morphological) traits failed to differentiate the putative species, but that canonical variates analysis resulted in a high degree of discrimination of the putative species and infraspecific taxa.

Many plants have been selectively bred to produce a maximum of THC (cannabinoids), which is obtained by curing the flowers. as a wild or escaped variety of the high-intoxicant type.In North America, cannabis, in the form of hemp, was grown for use in rope, clothing and paper. In 1940, Russian botanists Serebriakova and Sizov proposed a complex classification in which they also recognized C. The term hemp is used to name the durable soft fiber from the Cannabis plant stem (stalk).He considered the genus to be monotypic, having just a single species that he named Cannabis sativa L. stands for Linnaeus, and indicates the authority who first named the species). Cannabis sativa cultivars are used for fibers due to their long stems; Sativa varieties may grow more than six metres tall.Three species may be recognized: Cannabis sativa, Cannabis indica, and Cannabis ruderalis; C. sativa; or all three may be treated as subspecies of a single species, C. Cannabis has long been used for hemp fibre, for hemp oils, for medicinal purposes, and as a recreational drug.Industrial hemp products are made from cannabis plants selected to produce an abundance of fiber.At the top of a flowering plant, this number again diminishes to a single leaflet per leaf. Schultes and coworkers also conducted taxonomic studies of Cannabis in the 1970s, and concluded that stable morphological differences exist that support recognition of at least three species, C. indica is shorter, conical in shape, and has relatively wide leaflets, and C.

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. ruderalis is short, branchless, and grows wild in central Asia.

Cannabis normally has imperfect flowers, with staminate "male" and pistillate "female" flowers occurring on separate plants. Cannabis plants produce a group of chemicals called cannabinoids, which produce mental and physical effects when consumed. sativa subspecies into 13 varieties, including four distinct groups within subspecies culta. Laws prohibiting Cannabis in the United States and Canada specifically named products of C. Enterprising attorneys for the defense in a few drug busts argued that the seized Cannabis material may not have been C. Attorneys on both sides recruited botanists to provide expert testimony. Ruderalis is the informal name for the short plants that grow wild in Europe and central Asia.

Although monoecious plants are often referred to as "hermaphrodites", true hermaphrodites (which are less common) bear staminate and pistillate structures together on individual flowers, whereas monoecious plants bear male and female flowers at different locations on the same plant. Cannabinoids, terpenoids, and other compounds are secreted by glandular trichomes that occur most abundantly on the floral calyxes and bracts of female plants. Breeders, seed companies, and cultivators of drug type Cannabis often describe the ancestry or gross phenotypic characteristics of cultivars by categorizing them as "pure indica", "mostly indica", "indica/sativa", "mostly sativa", or "pure sativa". Cannabis is a popular recreational drug around the world, only behind alcohol, caffeine and tobacco.

However, the serration vein originates from lower down the central vein of the leaflet, typically opposite to the position of, not the first notch down, but the next notch. This has resulted in many reclassifications based on evolutionary systematics. They also commented that these analyses confirm the continuity of the Cannabis gene pool throughout the studied accessions, and provide further confirmation that the genus consists of a single species, although theirs was not a systematic study per se. Hillig, a graduate student in the laboratory of long-time Cannabis researcher Paul G. Another paper in the series on chemotaxonomic variation in the terpenoid content of the essential oil of Cannabis revealed that several wide-leaflet drug strains in the collection had relatively high levels of certain sesquiterpene alcohols, including guaiol and isomers of eudesmol, that set them apart from the other putative taxa. He also concluded there is little support to treat C. sativa at this time, but more research on wild and weedy populations is needed because they were underrepresented in their collection.

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. Several studies of Random Amplified Polymorphic DNA (RAPD) and other types of genetic markers have been conducted on drug and fiber strains of Cannabis, primarily for plant breeding and forensic purposes. Mahlberg at Indiana University, conducted a systematic investigation of genetic, morphological, and chemotaxonomic variation among 157 Cannabis accessions of known geographic origin, including fiber, drug, and feral populations. The authors assigned fiber/seed landraces and feral populations from Europe, central Asia, and Asia Minor to C. Narrow-leaflet and wide-leaflet drug accessions, southern and eastern Asian hemp accessions, and feral Himalayan populations were assigned to C. In 2005, Hillig published a genetic analysis of the same set of accessions (this paper was the first in the series, but was delayed in publication), and proposed a three-species classification, recognizing C. Hillig concluded that the patterns of genetic, morphological, and chemotaxonomic variation support recognition of C. In September 2005, New Scientist reported that researchers at the Canberra Institute of Technology had identified a new type of Cannabis based on analysis of mitochondrial and chloroplast DNA.

Lamarck based his description of the newly named species on plant specimens collected in India. In the early 20th century, the single-species concept was still widely accepted, except in the Soviet Union where Cannabis continued to be the subject of active taxonomic study. Janichevsky concluded that ruderal Cannabis in central Russia is either a variety of C. Cannabis for industrial uses is valuable in tens of thousands of commercial products, especially as fibre ranging from paper, cordage, construction material and textiles in general, to clothing. It also is a useful source of foodstuffs (hemp milk, hemp seed, hemp oil) and biofuels.