Cannabinoids are terpenophenolic compounds unique to
Cannabis. They are produced by glandular trichomes that occur on most aerial surfaces of the plant (Dayanandan and Kaufman, 1976
; Turner et al., 1978
). Approximately 61 cannabinoids are known to exist, although some of these are breakdown products or artifacts (Schultes and Hofmann, 1980
; Turner et al., 1980
).
The cannabinoids discussed in this paper are biosynthesized in an acidic (carboxylated) form and are decarboxylated upon heating and drying of harvested plant material (Doorenbos et al., 1971 ). They are here referred to in their decarboxylated form. Cannabigerol (CBG) is the direct precursor of cannabichromene (CBC), cannabidiol (CBD), and
9-tetrahydrocannabinol (THC) (Taura et al., 1995 , 1996 ; Morimoto et al., 1997 ). A homologous series of compounds with propyl side-chains is biosynthesized from cannabigerovarin (CBGV), including cannabivarichromene (CBCV), cannabidivarin (CBDV), and
9-tetrahydrocannabivarin (THCV), respectively (Fig. 1A–D) (Schultes and Hofmann, 1980 ). THC and/or CBD are generally produced in greatest abundance. However, THCV and less commonly CBDV may exceed the levels of THC and/or CBD in some plants (Baker et al., 1980 ). THC and THCV are primarily responsible for the euphoric effects of marijuana and hashish (McPartland and Russo, 2001 ).
Chemotaxonomy has a long history of use in the delimitation of
Cannabis taxa. Lamarck (1785)
emphasized the greater inebriant potential of
C. indica Lam. when he differentiated it from
C. sativa L. Names and descriptions of other putative species of
Cannabis have been published (reviewed in Schultes et al., 1974
; Small and Cronquist, 1976
). Of these, only
C. ruderalis Janisch. is commonly accepted.
Small (1979a) considered the amount of THC produced by Cannabis to be an "extremely important" taxonomic character and used gas chromatography (GC) to differentiate indica strains from sativa strains on the basis of their THC content (Small and Beckstead, 1973a , b ; Small et al., 1975 ; Small and Cronquist, 1976 ). Small and Cronquist (1976) favored a monospecific concept and assigned these two taxa to subspecies of C. sativa.
Numerous biochemical studies of
Cannabis plants grown from achenes ("seeds") of known geographic origin have been reported (Fetterman et al., 1971
; Fetterman and Turner, 1972
; Nordal and Braenden, 1973
; Small and Beckstead, 1973a
, b
; Turner et al., 1973
; Turner and Hadley, 1973a
, 1974
; Boucher et al., 1974
; Holley et al., 1975
; Small et al., 1975
; Rowan and Fairbairn, 1977
; Beutler and Der Marderosian, 1978
; Clark and Bohm, 1979
; Turner et al., 1979
; Fournier and Paris, 1980
; Hemphill et al., 1980
; Veszki et al., 1980
; de Meijer et al., 1992
). Forensic studies of
Cannabis examined marijuana and hashish samples of known origin, grown in a range of environments (Jenkins and Patterson, 1973
; Poddar et al., 1973
; Baker et al., 1980
, 1982
; Barni-Comparini et al., 1984
; Brenneisen and ElSohly, 1988
). In studies that used packed columns for gas chromatographic separations, CBC may sometimes have been mistaken for CBD because of their close retention times (Small and Beckstead, 1973a
; Turner and Hadley, 1973b
). Most botanical and forensic studies of
Cannabis lack voucher specimens for taxonomic identification. A notable exception is the systematic/forensic investigation by Small and coworkers that is referred to extensively herein (Small and Beckstead, 1973a
, b
; Small et al., 1975
; Small and Cronquist, 1976
; Small, 1979a
, b
).
The cannabinoid content of different strains of Cannabis is associated with their geographic origins. Extracts of Cannabis indica ("Indian hemp") were commonly used in Western medicine, while the common hemp of Europe was generally regarded as unsuitable for medicinal use (Winek, 1977 ). Small and Beckstead (1973a , b ) observed that most strains in their collection that produced high levels of THC originated from latitudes south of 30°N. They detected elevated levels of a cannabinoid presumed to be cannabigerol monomethylether (CBGM) in strains from northeast Asia. High levels of THCV were reported in Cannabis strains from southern Africa, India, Nepal, and eastern Asia (Merkus, 1971 ; Fetterman and Turner, 1972 ; Turner et al., 1973 ; Boucher et al., 1974 ; Baker et al., 1980 ).
The amounts of CBD and THC in an individual
Cannabis plant can be characterized both qualitatively and quantitatively (Hemphill et al., 1980
; Hillig, 2002
; Mandolino et al., 2003
).
Qualitative characterization involves determining a plant's THC/CBD ratio (the inverse ratio is sometimes used) and assigning it to a discrete chemical phenotype (chemotype). Fetterman et al. (1971) recognized two chemotypes: a THC/CBD ratio >1.0 characteristic of "drug-type" plants, and a THC/ CBD ratio <1.0 characteristic of "fiber-type" plants. Small and Beckstead (1973a , b ) also recognized an intermediate chemotype. According to their system of classification (that is used herein), chemotype I plants have a high THC/CBD ratio (>>1.0), chemotype II plants have an intermediate ratio (close to 1.0), and chemotype III plants have a low THC/CBD ratio (<<1.0).
The THC/CBD chemotype of a plant is determined at a young age and is stable beyond the seedling stage throughout the life of the plant (Barni-Comparini et al., 1984 ; Vogelmann et al., 1988 ).
In addition to the qualitative determination of THC/CBD chemotype, a plant can be characterized by the quantitative levels of cannabinoids within its tissues. These levels are likely determined by the interaction of several genes with a plant's environment. Numerous biotic and abiotic factors affect cannabinoid production including the
sex and maturity of the plant (Doorenbos et al.,1971
; Fetterman et al., 1971
; Small et al., 1975
),
daylight length (Valle et al., 1978
)
, ambient temperature (Bazzaz et al., 1975
)
, nutrient availability (Coffman and Gentner, 1977
; Bócsa et al., 1997
)
, and ultraviolet light intensity (Lydon et al., 1987
; Pate, 1994
)
. Quantitative levels of cannabinoids also vary among different tissues within a plant (Fetterman et al., 1971
; Hemphill et al., 1980
).
The amount of CBD or THC in the mature inflorescence of a pistillate plant (Cannabis is dioecious) may exceed 10.0% of its dry weight (d.w.), while the amount of these cannabinoids in the primary leaves is often <1.0% (Baker et al., 1982
; Barni-Comparini et al., 1984
).
