Cannabis (/ˈkænəbɪs/)[2] is a genus of flowering plants in the family Cannabaceae. The number of species within the genus is disputed. Three species may be recognized: Cannabis sativa, C. indica, and C. ruderalis. Alternatively, C. ruderalis may be included within C. sativa, all three may be treated as subspecies of C. sativa,[1][3][4][5] or C. sativa may be accepted as a single undivided species.[6] The genus is widely accepted as being indigenous to and originating from Asia.[7][8][9]
The plant is also known as hemp, although this term is often used to refer only to varieties of Cannabis cultivated for non-drug use. Cannabis has long been used for hemp fibre, hemp seeds and their oils, hemp leaves for use as vegetables and as juice, medicinal purposes, and as a recreational drug. Industrial hemp products are made from cannabis plants selected to produce an abundance of fibre. 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.[10]
Cannabis is an annual, dioecious, flowering herb. The leaves are palmately compound or digitate, with serrate leaflets.[11] 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.[12]
All known strains of Cannabis are wind-pollinated[13] and the fruit is an achene.[14] Most strains of Cannabis are short day plants,[13] with the possible exception of C. sativa subsp. sativa var. spontanea (= C. ruderalis), which is commonly described as "auto-flowering" and may be day-neutral.
Cannabis is predominantly dioecious,[13][15] having imperfect flowers, with staminate "male" and pistillate "female" flowers occurring on separate plants.[16] "At a very early period the Chinese recognized the Cannabis plant as dioecious",[17] and the (c. 3rd century BCE) Erya dictionary defined xi 枲 "male Cannabis" and fu 莩 (or ju 苴) "female Cannabis".[18] Male flowers are normally borne on loose panicles, and female flowers are borne on racemes.[19]