this info here explains it pretty good.
In 1924, Russian botanist D.E. Janichevsky concluded that
ruderal Cannabis in central Russia is either a variety of
C. sativa or a separate species, and proposed
C. sativa L. var.
ruderalis Janisch. and
Cannabis ruderalis Janisch. as alternative names.
[20] In 1929, renowned plant explorer
Nikolai Vavilov assigned wild or feral populations of
Cannabis in Afghanistan to
C. indica Lam. var.
kafiristanica Vav., and ruderal populations in Europe to
C. sativa L. var.
spontanea Vav.
[23][32] In 1940, Russian botanists Serebriakova and Sizov proposed a complex classification in which they also recognized
C. sativa and
C. indica as separate species. Within
C. sativa they recognized two subspecies:
C. sativa L. subsp.
culta Serebr. (consisting of cultivated plants), and
C. sativa L. subsp.
spontanea (Vav.) Serebr. (consisting of wild or feral plants). Serebriakova and Sizov split the two
C. sativa subspecies into 13 varieties, including four distinct groups within subspecies
culta. However, they did not divide
C. indica into subspecies or varieties.
[20][34] This excessive splitting of
C. sativa proved too unwieldy, and never gained many adherents.
Cannabis ruderalis.
In the 1970s, the taxonomic classification of
Cannabis took on added significance in North America. Laws prohibiting
Cannabis in the United States and Canada specifically named products of
C. sativa as prohibited materials. Enterprising attorneys for the defense in a few drug busts argued that the seized
Cannabis material may not have been
C. sativa, and was therefore not prohibited by law. Attorneys on both sides recruited botanists to provide expert testimony. Among those testifying for the prosecution was Dr. Ernest Small, while
Dr. Richard E. Schultes and others testified for the defense. The botanists engaged in heated debate (outside of court), and both camps impugned the other's integrity.
[27][28] The defense attorneys were not often successful in winning their case, because the intent of the law was clear.
[35]
In 1976, Canadian botanist Ernest Small
[36] and American taxonomist
Arthur Cronquist published a taxonomic revision that recognizes a single species of
Cannabis with two subspecies:
C. sativa L. subsp.
sativa, and
C. sativa L. subsp.
indica (Lam.) Small & Cronq.
[32] The authors hypothesized that the two subspecies diverged primarily as a result of human selection;
C. sativa subsp.
sativa was presumably
selected for traits that enhance fiber or seed production, whereas
C. sativa subsp.
indica was primarily selected for drug production. Within these two subspecies, Small and Cronquist described
C. sativa L. subsp.
sativa var.
spontanea Vav. as a wild or escaped variety of low-intoxicant
Cannabis, and
C. sativa subsp.
indica var.
kafiristanica (Vav.) Small & Cronq. as a wild or escaped variety of the high-intoxicant type. This classification was based on several factors including interfertility, chromosome uniformity, chemotype, and numerical analysis of
phenotypic characters.
[21][32][37]
Professors William Emboden, Loran Anderson, and Harvard botanist
Richard E. Schultes and coworkers also conducted taxonomic studies of
Cannabis in the 1970s, and concluded that stable
morphological differences exist that support recognition of at least three species,
C. sativa,
C. indica, and
C. ruderalis.[38][39][40][41] For Schultes, this was a reversal of his previous interpretation that
Cannabis is monotypic, with only a single species.
[42] According to Schultes' and Anderson's descriptions,
C. sativa is tall and laxly branched with relatively narrow leaflets,
C. indica is shorter, conical in shape, and has relatively wide leaflets, and
C. ruderalis is short, branchless, and grows wild in
central Asia. This taxonomic interpretation was embraced by
Cannabis aficionados who commonly distinguish narrow-leafed "sativa" drug
strains from wide-leafed "indica" drug strains.
[43]