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From Wikipedia, the free encyclopedia
This article is about the plant genus. For use as a psychoactive drug, see Cannabis (drug). For other uses, see Cannabis (disambiguation).
Cannabis (/ˈkænəbɪs/) is a genus of flowering plants that includes three putative varieties, Cannabis sativa, Cannabis indica, and Cannabis ruderalis. These three taxa are indigenous to Central Asia, and South Asia. Cannabis has long been used for fibre (hemp), for seed and seed oils, for medicinal purposes, and as a recreational drug. Industrial hemp products are made from Cannabis plants selected to produce an abundance of fiber. To satisfy the UN Narcotics Convention, some Cannabis strains have been bred to produce minimal levels of THC, the principal psychoactive constituent responsible for the “high” associated with marijuana. Marijuana consists of the dried flowers of Cannabis plants selectively bred to produce high levels of THC and other psychoactive cannabinoids. Various extracts including hashish and hash oil are also produced from the plant.
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 (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 that enables persons poorly familiar with the plant to distinguish a Cannabis leaf from unrelated species that have confusingly similar leaves (see illustration). As is common in serrated leaves, each serration has a central vein extending to its tip. 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 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 actually pass tangent to the notch, but often it will pass by at a small distance, and when that happens a spur vein (occasionally a pair of such spur veins) branches off and joins the leaf margin at the deepest point of the notch. This venation pattern varies slightly among varieties, but in general it enables one to tell Cannabis leaves from superficially similar leaves without difficulty and without special equipment. Tiny samples of Cannabis plants also can be identified with precision by microscopic examination of leaf cells and similar features, but that requires special expertise and equipment.
Cannabis normally has imperfect flowers, with staminate “male” and pistillate “female” flowers occurring on separate plants. It is not unusual, however, for individual plants to bear both male and female flowers. Although monoecious plants are often referred to as “hermaphrodites,” true hermaphrodites (which are less common) bear staminate and pistillate structures on individual flowers, whereas monoecious plants bear male and female flowers at different locations on the same plant. Male flowers are normally borne on loose panicles, and female flowers are borne on racemes. “At a very early period the Chinese recognized the Cannabis plant as dioecious,” and the (ca. 3rd century BCE) Erya dictionary defined xi 枲 “male Cannabis” and fu 莩 (or ju 苴) “female Cannabis”.
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 (= C. ruderalis), which is commonly described as “auto-flowering” and may be day-neutral.
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