The cannabis plant is often referred to as Cannabis sativa.
Most experts consider that there is only one type although some talk about Cannabis indica and Cannabis ruderalis as separate species.
The plant is annual that will grow successfully in a wide range of soils in both tropical and temperate regions.
Plants grown in mountainous regions tend to be shorter and stockier and typically flower several weeks earlier than plants grown closer to sea level.
Plants grown for drug use have traditionally been cultivated outdoors in hot climates.
In temperate climates, and even when grown under glass, summers may not be long enough to allow full development of the flowering parts.
Apart from the fibrous stem, which was once used for rope manufacture and is still used for other purposes, the two main drug products have been herbal cannabis and cannabis resin.
In the past 10 to 20 years, a number of horticultural developments such as propagation by cuttings, hydroponics and artificial control of "day" length using special lights have led to the widespread development of indoor cultivation of cannabis.
The plant is the only known natural source of cannabinoids which are to be found in the special glands situated mostly around the flowering parts.
Herbal cannabis or grass: is the dried flowering tops with or without variable amounts of leaves, stems and seeds.
Sinsimilla (Spanish for without seeds): refers to seedless flowering tops which have the greatest concentration of THC (tetrahydrocannabino) but the term has more or less been replaced by the term "skunk".
Low grade herbal cannabis often contains more of the leaves which contain less THC than the flowering tops.
Skunk: is the common name given to varieties of cannabis that have cross bred Cannabis sativa with Cannabis indica strains.
The name derives from the smell given to the first cross breed.
These varities have been developed for three key attributes, firstly to produce plants that have shorter flowering periods, secondly to increase yield and thirdly to increase potency.
However the potency levels are also heavily dependent on the skill of the grower and the amount of sunshine.
In European climates skunk varieties tend to be grown indoors under artificial lights, often hydroponically.
Cannabis resin: is obtained by sieving or otherwise separating and compressing the flowering tops.
This the most common type of recreational cannabis in the UK representing around 70% (IDMU) of the UK market.
The cheapest variety is called soap bar which originates from Morocco and is often adulterated with a wide range of chemicals and substances.
Soap bar averages around 4-5% THC. However throughout the last few decades specialty resins that average over 20% have been available although in limited supply.
Cannabis (hash) oil is a derived product made by extraction of THC from either herbal cannabis or cannabis resin.
Hash oil is the most potent form of recreational cannabis with THC levels ranging from 35 to over 50%.
However there has never been a significant demand for it and thus it remains relatively rare
Hydroponics: A method of growing a plant in water containing dilute nutrients. Often artificial lighting is used to provide optimum control. Many vegetables are commercially grown this way.
Cannabinoids: The major active principle in all cannabis products is Delta 9-tetrahydrocannabinol (THC).
Although sometimes known as dronabinol (an international non-proprietary name), naturally occurring Delta 9-tetrahydrocannabinol is not chemically identical to synthetic dronabinol.
Other closely related substances that occur in cannabis include Cannabidiol (CBD) and, in aged samples, cannabinol (CBN) both of which have quite different pharmacological effects to THC.
Other compounds include the cannabivarins and cannabichromenes; they are all collectively known as cannabinoids.