19.1 Introduction
The cannabis plant (Cannabis sativaL.), a member of the family Cannabaceae, has
been cultivated by humans since the beginning of recorded history—it’s use as a
medicinal and mood altering agent dates back to 7000 B.C. (Elsohly and Slade 2005 ;
Mechoulam 2005 ; Clarke and Merlin 2013 ). Wild and cultivated forms of the can-
nabis plant exhibit considerable morphological variation. Some taxonomic studies of
the genus suggest a monotypic genus,C. sativaLam, while other researchers have
suggested thatCannabisis comprised of three species—Cannabis sativaL,C. indica
Lam andC. ruderalisJanisch, also sometimes referred to as“indica”,“sativa”, and
“ruderalis”sub-species withinC. sativa(Schultes et al. 1974 ; Small and Cronquist
1976 ; Hillig 2005 ; Potter 2009 ; Chandra et al. 2013 ; Sawler et al. 2015 ). Among the
three sub-species,sativaandindicaare cultivated by marihuana growers, and they
have different chemotypes and show different effects on the human body when con-
sumed. By comparison, hemp, also classified asC. sativa,is morphologically indis-
tinguishable from marijuana but is grown for itsfibre and seed, and contains little to no
mood altering chemicals (Sawler et al. 2015 ; Small 2015 ).
19.2 Origins of Genetic Diversity in Cannabis
The origin of cannabis is believed to be central Asia, northwest Himalayas and
possibly eastern China (summarized in Hillig 2005 ), geographic areas where hops
(Humulus lupulusL.), the closest relative to cannabis, is also reported to have
originated from (Potter 2009 ). It is thought that the cannabis plants were spread
from this region to areas north and south of the mountain range. Scientists are
uncertain whether this spread resulted from humans cultivating and selecting plants
for seed,fibre, and its medicinal qualities (Small and Cronquist 1976 ), or whether
spread from its origin occurred prior to human intervention (Hillig 2005 ).
Nevertheless, it is widely assumed that the Himalayas helped the gene pool of
cannabis diverge (Hillig 2005 ). Spread of the plants northward and westward from
the origin and as far south as northern Africa, is believed to have resulted in a
population described as“sativa”. Spread of plants to equatorial Africa, eastward to
Pakistan, Afghanistan, and China and later to Latin America, gave rise to popu-
lations known as “indica”. Finally, the “ruderalis” group which consist of
low-potency ruderal (road-side) plants are mostly found in Eastern Europe (Potter
2009 ) and Central Asia (Hillig 2005 ). This sub-species contains plants that are
weedy and not used forfibre or seed production.
The movement and establishment of cannabis plants in different geographic
regions is believed to have resulted in the evolution of indigenous“landrace”
strains. These landraces (or highly diverse local genetic populations) are often
described by their geographic origin e.g.‘Kilmanjaro’originates from East Africa.
396 Z.K. Punja et al.