I'm really curious about the broad subject of sativa vs. indica, genomes, landrace, and what it actually means to be 100% sativa or 100% indica. Here's a helpful start to the discussion, from Kevin McKernan's Kannapedia: (underlines added)
Cannabis Sativa vs. Indica
The most accepted way of distinguishing indica versus sativa is by appearance, or what scientists refer to as morphology. Sativa plants are tall, loosely branched and have long, narrow leaves. They are usually grown outdoors and can reach heights of up to 20 feet. Indica plants are short, densely branched and have wider leaves. They are better suited for growing indoors. However, no scientific study has confirmed these differences, and there is some doubt about their accuracy. In fact, history suggests a much simpler difference between indica and sativa. The original classification of Cannabis indica was made by French biologist Jean-Baptiste Lamarck in 1785. Lamarck observed that certain marijuana plants from India were intoxicating and could be made into hashish. But traditional hemp crops, which were more common in Europe, had no mind-altering effect. He came up with the name Cannabis indica to distinguish Indian cannabis from European hemp, which was known at the time as Cannabis sativa. Likewise, Cannabis indica was specifically recognized as a therapeutic in Western medicine during the 1800s. Scientists that have studied the differences between indica and sativa have come up with a number of theories based on genetics. The prevailing theory focuses on the genetic production of THC and CBD, which is why indica plants have high THC:CBD ratios and sativa plants have high CBD:THC ratios. Many strains produce varying amounts of both enzymes due to hybridization, or cross breeding, of the gene pools; this explains why some sativas are rich in THC and some indicas are not.
This is saying that the commonly accepted difference in the morphology—i.e. the plant size, shape, and leaf structure—is not a reliable determinant of sativa vs. indica. Instead, chemotypic differences are important, meaning the ratios of the cannabinoids, chiefly THC and CBD.
I think what they are referring to as the "prevailing theory" is from a scientific article titled,
A chemotaxonomic analysis of cannabinoid variation in Cannabis (Cannabaceae), by Hillig and Mahlberg, 2004.
From the Hillig/Mahlberg article (underlines added):
"This study confirms that the THC/CBD ratio of individual
Cannabis plants can be assigned to one of three discrete chemotypes. The limits between chemotypes coincide with those reported by
Vollner et al. (1986). As expected, plants with
high levels of THC were common within the two drug biotypes of C. indica. However, plants with relatively high levels of THC were also common within the hemp and feral biotypes of this species. In contrast, most plants assigned to
C. sativa had relatively low levels of THC. Because chemotype I, II, and III plants were found in both species, the chemotype of an individual plant is of limited use for chemotaxonomic determination of species
membership."
This is drawing a distinction, saying that it's common to find high THC in plants classified as indica, whereas most plants classified as sativa have relatively low levels of THC. So, this is making reference to "original" sativas, i.e. pure landraces and feral (wild) sativas, as opposed to modern-day sativas that contain genetics from indicas.
But, they are also saying that this distinction isn't sufficient to determine "species
membership"—i.e. sativa vs. indica. To resolve this, the authors look specifically at chemotype I (type one). Before we consider chemotype I, here are the cannabis "biotypes" from the Hillig/Mahlberg article...
Table 1. Taxonomic circumscription of the Cannabis germplasm collection based on a previous analysis of allozyme allele frequencies. The assignment of accessions to putative taxa was previously published (Hillig, 2004)
* Narrow-leaflet drug (NLD) strains from the Indian subcontinent and other drug producing regions.
Now, looking specifically at chemotype I, which is high THC and very low CBD... (underlines added)...
"It was estimated that chemotype I individuals comprised <25% of each population for all but two of the 89 accessions
assigned to C. sativa and >25% of each population for all but four of the 62 accessions
assigned to C. indica. This appears to be a reasonable guideline for differentiation of the two species, in conjunction with other taxonomic traits. The advantage of this approach over the method of Small and Cronquist (1976) for differentiating
sativa from
indica (regardless of taxonomic rank) is that
the frequency of chemotype I plants in a given population is stable from one generation to the next (assuming Hardy–Weinberg equilibrium) and not influenced by biotic and abiotic factors that affect the quantitative production of cannabinoids.
For populations that have been purposely selected for a fixed chemotype, geographic origin and morphological traits are better indicators of species
membership (Hillig, 2004, in press)."
* Accession refers to the plant materials collected from a particular area. I think this means, you could have an accession containing many individuals of a particular variety or strain, representing various phenotypes.
This is making an estimation that, 98% of the accessions assigned to the sativa species indicate
less than 25% of populations are chemotype I individuals (high THC, very low CBD). And, 91% of the accessions assigned to indica indicate
more than 25% of the populations are chemotype I individuals. This supports the idea that "original" sativas—i.e. hemp landraces and wild sativas from eastern Europe—are low in THC. Similarly, "original" indicas—i.e. those listed in Table 1 above as
indica (either indica hemp landraces, wild indicas, narrow-leaf "drug" strains, or wide-leaf "drug" strains) are high/higher in THC.
***
Some CONCLUSIONS**:
- Original sativas were tall, narrow leaf plants with low THC and varying amounts of CBD, originating from Europe, Asia Minor (Turkey), and Central Asia—not south, east (China), or southeast Asia.
- Original indicas were short, wide leaf plants with high THC, originating from south Asia and east Asia (China), including India, Nepal, Afghanistan, and Pakistan.
- It makes sense that the high-THC sativas that were developed in southeast Asia (e.g. Thailand) were tall-growing, narrow-leaf strains, hybridized with high-THC indica strains.
- What we consider as a modern-day sativa isn't the same as the original sativas. Modern-day, high-THC sativas are the result of hybridization.
- Type II and Type III strains, containing high amounts of CBD, are likely the result of breeding with original (or close to original) sativa genetics, or breeding with hybrids that contain original sativa genetics.
- Sativas are actually the original CBD plants! This explains why many or most of the high-grade, type III CBD strains are classified as sativas. (High-grade meaning in the 15-20% CBD range.)
** I have omitted any discussion of ruderalis.
Next I'll attempt to relate all this to landraces, and comment on sativa/indica in terms of effects rather than either morphology or chemotypes. And, I'll try to bring it all together and answer the question, what does it really mean to be 100% sativa or 100% indica?
