50 Years of Cannabis Breeding: From the Hippie Strain to the Hexaploid

In the 1970s, botanists could not even agree on whether cannabis was one species or several. Today there are plants with three times as many chromosome sets as the original, and, in a first study, up to 65 percent more total cannabinoids. How we got here is a short history of plant breeding in fast-forward.

The Start: A Plant Nobody Really Knew

In 1976, two botanists drew a line under a 250-year-old debate. Ernest Small and Arthur Cronquist published a paper in the journal Taxon with the plain title “A practical and natural taxonomy for Cannabis” (Small & Cronquist, 1976). Their conclusion: there is only one biological species, Cannabis sativa L., with two subspecies and a wild and a cultivated variety each. The labels “Sativa” and “Indica” marketed today are, taxonomically, more of a marketing construct than a botanical finding, a view that contemporary reviews confirm (McPartland, 2018).

What existed as breeding at that time ran largely underground. In California and the Netherlands, hobby breeders crossed landraces (regional, naturally adapted original strains) from Afghanistan, Mexico and Thailand and named the results Skunk #1, Northern Lights or Haze. Scientific genetics happened in parallel elsewhere: on fiber hemp in Wageningen, on industrial hemp in Bologna.

The Mendel Turn: One Locus Governs the THC-CBD Ratio

In 2003, Etienne de Meijer and his Italian team delivered one of the most important findings in cannabis genetics. In the journal Genetics, they showed that the ratio of THC to CBD in a plant is controlled by a single locus with two co-dominant alleles (de Meijer et al., 2003). That sounds technical, but in plain terms it means: cross a THC-dominant with a CBD-dominant plant and you can predict the cannabinoid profile of the offspring like Mendel’s peas.

That opened the door to targeted variety development. Not by chance, a first wave of CBD-dominant hemp varieties appeared on the market in the years that followed, and the idea of cleanly defining “chemical varieties” or chemotypes became the standard (Russo, 2019).

2011: Cannabis Gets a Genome

The next big leap came out of Toronto. Harm van Bakel and colleagues sequenced the genome of the drug strain Purple Kush in 2011 and compared it with the fiber hemp Finola (van Bakel et al., 2011). The result: around 534 megabases, 30,000 genes and, at the molecular level, clear differences in the cannabinoid biosynthesis pathways. Four years later, a team in Canada backed this up with marker data: hemp and marijuana are genetically clearly separate populations, but variety names often correlate surprisingly poorly with the underlying genetics (Sawler et al., 2015).

Then, in 2018, the keystone: a high-resolution map showed that the genes for THC and CBD synthase sit in extremely rearranged genome regions, packed with jumping elements (Laverty et al., 2019). That explains why cannabinoid profiles can vary so strongly between varieties, and it provides the basis for modern marker-assisted selection. The fiber hemp field kept pace in parallel with its own reviews and Wageningen programs (Salentijn et al., 2014).

Domestication: Older and More East Asian Than Thought

For a long time, Central Asia counted as the cradle of cannabis. In 2021, Guangpeng Ren and colleagues presented a resequencing of 110 accessions worldwide in Science Advances and shifted the story eastward (Ren et al., 2021). Cannabis was, accordingly, domesticated around 12,000 years ago in East Asia; the sativa– and indica-type lines known today are the result of later selection. The original wild forms are largely extinct, which makes highland landraces from Afghanistan and the Hindu Kush a genetic treasure (McPartland & Small, 2020).

If you want the full picture of genome research, you will find the roadmap in a review article: available assemblies, GWAS studies, sex determination, cannabinoid clusters (Hurgobin et al., 2020). The Cannabis sativa of 2026 is genetically better understood than many classic crops.

Polyploids: The Latest Wave

That leaves the current trend, and it is old and new at once. Polyploidy means a plant has three (triploid), four (tetraploid) or even six (hexaploid) chromosome sets instead of the usual two. This has worked in many crops for decades; in cannabis there were attempts early on, but it stayed a niche (Parsons et al., 2019).

Triploids have a practical charm: they are largely sterile and barely form seeds. For flower production that is a real advantage: no unwanted pollination and more even flower mass. A controlled study from Connecticut confirmed in 2024 that triploid cannabis plants keep pace with diploids in growth and flower yield, but their seed formation is dramatically reduced (Kurtz et al., 2024).

And then comes the latest paper, fresh from Korea: Tae Hyun Ha and his team presented the first stable hexaploid cannabis plants in early 2026 (Ha et al., 2026). With an optimized colchicine treatment and multi-generation selfing, they arrived at plants whose hexaploid status is cleanly confirmed by flow cytometry and chromosome counting. The study reports roughly 65 percent higher total cannabinoid content, about 60 percent more plant height and 2.7 times the dry flower mass compared with diploids. Whether this holds up in practice is for follow-up research to show, but the trend is clear.

What Has Changed in 50 Years

The plant is the same, what we know about it is not. In 1976 there was an argument over whether cannabis is one species. In 2026, cannabinoid profiles can be dialed in by marker selection, the domestication history reconstructed and varieties bred with triple the chromosome count. What remains open: most variety names on the market still correlate poorly with the actual genetics, and the diversity of the original landraces is under threat (Andre et al., 2016). So keep an eye on the next wave of cannabis research. It will probably not come from Wageningen or Toronto, but from where polyploids, domestication genetics and variety identity meet.

Take-Aways

  • One species, many chemotypes: cannabis is botanically a single species; the THC-CBD ratio depends on a single locus.
  • Genome since 2011, map since 2018: modern cannabis breeding is marker-assisted and no longer gut feeling.
  • Domestication in East Asia, around 12,000 years ago, not in Central Asia as long assumed.
  • Polyploids are the current playing field: triploids (sterile, high-yielding) are established, hexaploids just fresh in the race, with higher cannabinoid values reported in a first study.
  • Variety names are not genetics: what is sold as “Skunk”, “OG Kush” or “Indica” says little about the actual genetic relationship.

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