Cannabis sativa
Cannabis sativa is a herb that has been used by humans throughout recorded history for its fiber, known as hemp, for its psychological and physiological effects and for the nourishment of its oil-bearing seeds. Different parts of the plant have different uses, and different varieties are cultivated in different ways and harvested at different times, depending on the purpose for which it is grown.

# Species, subspecies, and varieties
The following taxonomic treatment of Cannabis was published in 1976 by Ernest Small and Arthur Cronquist.  Other taxonomic treatments of Cannabis are valid, and utilized by some botanists.

## C. sativa subsp. sativa

### C. sativa subsp. sativa var. sativa
Correct name: Cannabis sativa L. subsp. sativa var. sativa
This taxon includes hemp landraces and cultivars grown for fiber or seed production.  Fiber strains are usually tall and unbranched.  Seed strains are often shorter, and may be branched or unbranched.  Some strains are monoecious.  Plants of certified industrial hemp strains produce a relatively high ratio of CBD to THC (about 20:1), and are not suitable for drug use.

### C. sativa subsp. sativa var. spontanea
Correct name: Cannabis sativa L. subsp. sativa var. spontanea (Vavilov) Small & Cronq.
Synonym: C. ruderalis Janisch.
This taxon includes wild or feral Cannabis plants.  In the absence of selective breeding, these plants have lost many of the traits they were originally selected for, and have acclimatized to their locales.  Plants of this type are often short, branchless, and early-flowering.  The plants usually have low levels of cannabinoids, and a low ratio of THC to CBD, and thus are of little use as a source of drugs.  However, so-called "indica" drug strains are sometimes cross-bred with "ruderalis" to produce high THC plants having the hardiness and reduced height of "ruderalis".
The term "ruderal" was originally used in the former Soviet Union to describe populations of hemp that had escaped cultivation and adapted to the surrounding region.  Plants of this type are widespread throughout central and eastern Europe, including Lithuania, Belarus, Latvia, and Estonia.  Similar populations can be found in most of the areas where hemp cultivation was once prevalent.  The most notable region in North America is the midwest, though populations occur sporadically throughout the United States and Canada. These plants have escaped from cultivation more recently, and often grow larger than the ruderal plants in Europe.
Cannabis users often call this feral Cannabis "ditch weed."  Outside of its native range, it is regarded as an invasive plant.  Despite years of government-sponsored eradication programs, these feral plants still remain in bountiful abundance.
It has several times been proposed that this taxon be recognized as a distinct species, called C. ruderalis.

## C. sativa subsp. indica

### C. sativa subsp. indica var. indica
Correct name: Cannabis sativa L. subsp. indica (Lam.) Small & Cronq. var. indica (Lam.) Wehmer
Synonym: C. indica Lam.
This taxon includes two types of Cannabis cultivated for drug production, commonly referred to by Cannabis aficionados as "sativa" and "indica".
Narrow-leafed "sativa" drug strains and landraces are native to the Indian subcontinent, and are also cultivated in Africa, South and Central America, the Caribbean basin, and in other marijuana producing regions.  These strains are usually tall, laxly branched, and relatively late-maturing.  They have largely been replaced by so-called "indica/sativa" hybrids by commercial Cannabis growers because the hybrids often yield a larger crop in a shorter period of time.
Wide-leafed "indica" drug strains are traditionally cultivated in northwest India, Afghanistan, and Pakistan for the production of hashish, and may have originated in the Hindu-Kush or Tian Shan mountain range.  Due to the often harsh and variable climate of those regions, these strains and landraces are better suited for cultivation in temperate climates.  Plants of this type are relatively short, conical, and densely branched, having characteristcally wide leaflets, and tend to produce a lower ratio of THC to CBD than the narrow-leafed drug strains   Although many commercially available varieties are genetically fixed to produce relatively high levels of THC and low levels of CBD (which is not psychoactive), some users report more of a "stoned" and less of a "high" effect from these varieties compared to the narrow-leafed strains.  Differences in the terpenoid content of the essential oil may account for some of these differences.
Anecdotal evidence suggests that when used recreationally, highs from "sativa" strains tend to produce clearer, "cerebral" highs, whereas highs from "indica" strains produce more "druggy" body highs, with emphasis on drowsiness, slight loss of motor coordination, and increase appetite ("munchies"). To date, no undisputable chemical or pharmacological basis for these differing effects has been discovered.
It has often been proposed that this taxon be recognized as a distinct species, C. indica.  Most recently, on the basis of genetic, morphological, and chemotaxonomic analyses, Hillig assigned both the narrow-leaflet and wide-leaflet drug "biotypes", as well as southern and eastern Asian hemp (fiber/seed) landraces and wild Himalayan populations, to C. indica.

### C. sativa subsp. indica var. kafiristanica
Correct name: Cannabis sativa L. subsp. indica (Lam.) Small & Cronq. var. kafiristanica (Vavilov) Small & Cronq.
Synonym: C. indica Lam. var. kafiristanica Vavilov.
This taxon includes wild or feral plants, mostly confined to the Indian subcontinent and other regions where Cannabis is grown for drug use and has escaped from cultivation.  Individual plants may have low, similar, or high levels of THC relative to CBD.  Plants with relatively high levels of 9-tetrahydrocannabidivarin (THCV) and/or cannabidivarin (CBDV) are also common in this group.  Compared with wild or feral plants of var. spontanea, plants of this taxon are often taller and more branched. The achenes are usually very small.  The inflorescenses of pistillate plants are often elongated, and the fruits (achenes) drop off the plants as they mature.

# Common uses
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. The flowers (and to a much lesser extent the leaves, stems, and seeds) contain psychoactive and physiologically active chemical compounds known as cannabinoids that are consumed for recreational, medicinal, and spiritual purposes. When so used, preparations of flowers (marijuana) and leaves  and preparations derived from resinous extract (hashish) are consumed by smoking, vaporizing and oral ingestion. Historically, tinctures, teas, and ointments have also been common preparations.

# Plant physiology
Cannabis reproduces sexually. The flowers of the female plant are arranged in racemes and can produce hundreds of seeds. Males plants shed their pollen and die several weeks prior to seed ripening on the female plants. Although genetic factors dispose a plant to become male or female, environmental factors including the diurnal light cycle can alter sexual expression. Naturally occurring monoecious plants, with both male and female parts, are either sterile or fertile but artificially induced "hermaphrodites" (a commonly used misnomer) 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 requires 18 hour light, 6 hour dark (more than 12 hours of light to stay vegetative). Flowering usually occurs when darkness exceeds 12 hours per day, and water is cut down The flowering cycle can last anywhere between four to six 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.
- Cultivars primarily cultivated for their fiber, 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 industrial hemp, with concentrations of psychoactive compounds far too low to be useful for that purpose, and marijuana.

# Pharmacology
Although the main psychoactive chemical compound in Cannabis is 9-tetrahydrocannabinol (THC), the plant is known to contain about sixty cannabinoids; however, most of these "minor" cannabinoids are only produced in trace amounts. Besides THC, another cannabinoid produced in high concentrations by some plants is cannabidiol (CBD), which is not psychoactive but has recently been shown to block the effect of THC in the nervous system. 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 natural Cannabis preparations.
Most commonly available Cannabis contains below 8% THC. Selective breeding and modern cultivation techniques like hydroponics have produced varieties with more than 15% THC. With varieties containing below 1% THC, such as those specifically cultivated for use as hemp, smoking may produce lightheadedness or mild headache but not intoxication. The THC content is also affected by the sex of the plant, with female plants generating substantially more resin than their male counterparts. Seedless floral clusters derived from unpollinated female plants usually have a higher THC content than seeded inflorescences, and are commonly known as sinsemilla (Spanish: "without seed").