Cannabis sativa, also known as hemp, is a species of Cannabis. It is a dioecious, annual herb. It has been used by humans throughout recorded history for its fiber, for its psychological and physiological potential as a source of drug material, and for the nourishment and oil of its seeds. Different parts of the herb have different uses and different varieties are cultivated in different ways, and harvested at different times, depending on the purpose for which the herb is grown.
The tough fiber of the plant, cultivated as hemp, has numerous textile uses. Its seed, chiefly used as caged-bird feed, is a valuable source of protein, energy, and long-chain fatty acids, and also contain oil that can be used to make paints, varnishes and soaps.
Most concentrated in the resin of female plant are psychoactive and physiologically active chemical compounds known as cannabinoids that are consumed for recreational, medicinal, and spiritual purposes. When so used, preparations of flowers and leaves, sometimes called marijuana, and preparations derived from resinous extract, sometimes called hashish, are usually consumed by inhaling a vapor released by smoking or heating, or by oral ingestion. Historically, tinctures, teas, and ointments were also common preparations.
Some botanists assign the drug strains of Cannabis to a separate species, Cannabis indica (Hillig, K.W. and P. G. Mahlberg. 2004. A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae). American Journal of Botany 91: 966-975). Others consider all Cannabis plants to belong to the species Cannabis sativa (Small, E. and A. Cronquist. A practical and natural taxonomy for Cannabis. Taxon 25: 405-435).
Cannabis reproduces sexually. The flowers of the female plant, in cannabis usually called buds, are arranged in racemes and can produce hundreds of seeds. Males reach sexual maturity several weeks prior to females. Although genetics disposes a plant to become male, environmental factors, including the diurnal light cycle, can alter the sex. Natural hermaphrodites, with both male and female parts, are either sterile or fertile but artificially induced hermaphrodites can have fully functional reproductive organs. 'Feminized' seed sold by many commercial seed suppliers are derived from artificially hermaphrodytic females that lack the male gene or by treating the seeds with hormones or silver thiosulfate.
A cannabis plant in the vegetative growth phase of its life cycle can thrive under twenty-four hour daylight conditions, although some growers advocate a small rest period to avoid overstressing the plant. Flowering usually occurs when darkness exceeds eleven hours per day. The flowering cycle can last anywhere between six to twelve weeks, depending on the strain and environmental conditions.
In soil, the optimum pH for the plant is 6.5 to 7.2. In hydroponic growing, the nutrient solution is best at 5.2 to 5.8, making cannabis well-suited to hydroponics because this pH range is hostile to most bacteria and fungi.
Broadly, there are three main Cultivar Groups of cannabis that are cultivated today:
- Cultivars primarily cultivated for their fibre, characterized by long stems and little branching.
- Cultivars grown for seed from which hemp oil is extracted.
- Cultivars grown for medicinal or recreational purposes. A nominal if not legal distinction is often made between hemp, with concentrations of psychoactive compounds far too low to be useful for that purpose, and marijuana.
Though the main psychoactive chemical compound in cannabis is Delta-9-tetrahydrocannabinol (THC), the plant is known to contain about sixty cannabinoids. One other cannabinoid of particularly high concentration in some plants is cannabidiol (CBD), which is not psychoactive but modifies the effect of THC. Differences in the chemical composition of cannabis varieties may produce different effects in humans. Synthetic THC, called dronabinol, does not contain CBD, CBN, or other cannabinoids, which is one reason why its pharmacological effects may differ significantly from those of cannabis preparations.
Most commonly available marijuana contains below 8% THC. Selective breeding and modern cultivation techniques like hydroponics have produced varieties with more than 15% THC. With varieties containing below 2% THC, such as those specifically cultivated for use as hemp, smoking may produce lightheadedness or mild headache but not inebriation. The THC content is also affected by the sex of the plant, with female plants generating substantially more resin than their male counterparts. Seedless varieties derived from unpollinated female plants have high THC content and are traditionally known as sinsemilla (Spanish: "without seed").