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Cannabaceae: Mapping the Cannabis Family Tree

May 14, 2020 | by Nicole Gleichmann

Cannabaceae: Mapping the Cannabis Family Tree

Cannabis plants have been a central part of human culture for thousands of years. In fact, cannabis was one of the earliest domesticated plant species. While research into the evolution and genetics of cannabis was stifled for nearly a century, increasing legality is sparking new research into the history of this beneficial and versatile plant.

In this article, we’re going to explore the cannabis family tree, including its evolution and taxonomic classification, for those curious about the history of this medicinal plant.


Cannabis and other genera

Cannabis belongs to the family Cannabaceae, which evolved either alongside or from the family Urticaceae around 34 million years ago. The Cannabaceae family is found throughout most of the world, with the highest abundance throughout temperate regions of the Northern Hemisphere.

Cannabaceae includes roughly 170 species from 10 genera: Cannabis (hemp and marijuana), Humulus (hops), and eight genera that were formerly in the Celtidaceae (or hackberry) family. Prior to the 21st century, the Cannabaceae family was only thought to include the Cannabis and Humulus genera. It wasn’t until 2003 that researchers merged Celtidaceae and Cannabaceae based on genetic evidence.

Even though the Cannabaceae family name was adopted and the Celtidaceae name retired, experts believe that the name Celtidaceae would better reflect the family’s relation because the Cannabaceae lineage derived from the Celtidaceae. However, nomenclatural priority is given to the oldest name, which was Cannabaceae.

If you were to see species from the Cannabis, Humulus, and Celtidaceae genera together, you might be surprised at how different they appear. While Humulus and Cannabis are herbal plants, Celtidaceae species are all trees.

The majority of species in the Cannabaceae family belong to the Celtidaceae family, particularly the Celtis and Trema genera. However, it’s the species belonging to Cannabis and Humulus that possess value to humans as agricultural crops.

Humulus plants are most well-known for their use in brewing beer. They’re also used in other fermentations and as herbal supplements.

Cannabis is the most versatile genera in the Celtidaceae family, industrially speaking. Its various uses include the following:

  • Its nutritious seeds have been cultivated by humans since at least 10,000 years before present (BP).
  • Its fibers have been used for things like fabric since at least 5600 BP.
  • Its resin-rich flowers have been used for religious, medicinal, and recreational use since at least 2700 BP.

Today, hemp plants are cultivated for their seeds and fiber while marijuana plants are grown for their medicinal and recreational properties.


The origins of cannabis

Scientists have known for centuries that cannabis evolved in central Asia, but researchers had to overcome multiple challenges to deduce a more specific location.

Print fossils of cannabis are rare, leaving researchers to examine microfossils of cannabis pollen. Unfortunately, Asian cannabis pollen closely resembles one of its close relatives, the common hop plant, making it difficult to analyze the fossil record. The inconclusive fossil evidence hindered researchers from identifying the exact origin of cannabis, until last year.

In 2019, researchers from the University of Vermont finally narrowed down the origin of cannabis. To do so, the scientists collected data from 155 fossil pollen studies dating back to 1930. Next, they used ecological proxies to separate the hop pollen from the cannabis pollen.

Cannabis plants grow best in sunny areas, the same ecological conditions favored by grasses. Hop plants, however, share their ecological preferences with trees, growing in wooded areas. By analyzing other pollen fossils from the same archaeological dig sites, the scientists identified which fossils were cannabis plants and which were hop plants.

According to their findings, the cannabis center of origin was the northeastern Tibetan Plateau near Qinghai Lake. From there, the cannabis plant dispersed to Europe (around 6 million years ago), eastern China (around 1.2 million years ago), and India (around 33 thousand years ago).


How did cannabis spread across the globe?

To understand how cannabis traveled around the world, we must go back to the time when our ancestors lived as nomadic hunter-gatherers.

Cannabis plants grow best in sunny, warm river valleys in soils with high nitrogen content. These areas are the same habitats where our hunter-gather ancestors thrived.

Because the cannabis plant’s preferable growing conditions were near water in areas with human activity, humans and hemp interacted long before the agricultural revolution.

In these early days, researchers postulate that hunter-gatherers foraged the nutritious cannabis seeds. Because eating large quantities of these seeds could lead to a psychoactive experience, religious use in these early days is feasible.  

As nomadic people traveled, cannabis seeds were dispersed across Asia. Evidence of cannabis exists in 27,000 BP in the Czech Republic and 10,000 BP in Japan.

At some time during human’s interaction with cannabis, this plant began to evolve through artificial selection in a process termed domestication. Over time, humans would selectively breed for traits that produced strong fiber, psychoactive effects, and optimal nutrition.

Hemp fiber was used for clothing and ropes in China at least as far back as 5000 to 6000 years ago. Hemp was a valuable crop in China, being used to create paper, crossbow stings, and ship sails.

Ancient texts tell us of cannabis used as medicine by 4900 BP in China, 3600 BP in India, and 3600 BP in Egypt. During this time and thereafter, cannabis seeds were heavily traded, expanding its habitat throughout Europe, Asia, and eventually to Africa. It wasn’t until the 1600s that cannabis made its appearance in the western hemisphere.

Over this long history, cannabis has been valuable as a source of food, fiber, medicine, religion, and recreation. Its versatility of use is one reason why cannabis has remained an important crop for thousands of years.


Cannabis genus and species

Ask most cannabis afficionados today how many species of cannabis there are and you’ll probably be told there are two: Cannabis sativa and Cannabis indica. Speak with a botanist and you’ll get a much different answer.

Botanical taxonomists have not come to a consensus on the taxonomic classification of cannabis. What makes this matter tricky is this: to differentiate between species, it’s necessary to understand the evolutionary history of a plant. Thanks to the early human intervention in cannabis evolution and dispersal, we simply do not have this information.

Thousands of years of widespread domestication resulted in unaltered wild cannabis plants disappearing. And the cannabis plants that humans breed around the world have been heavily cross-bred and selected for certain traits, resulting in a complicated mixture of genes.

Another challenge facing scientists has been the legal status of cannabis. For decades, research into cannabis has been restricted. These restrictions are only now beginning to loosen, allowing researchers to explore more about the history of this plant.

With the limited data available, some taxonomists argue that all cannabis plants fall under one species, Cannabis sativa. Their argument is that every type of cannabis plant, whether labeled hemp, marijuana, C. sativa, or C. indica, can breed and produce viable offspring. This would classify C. indica as a subspecies of C. sativa.

Yet, others believe that the cannabis genus comprises three distinct species (based on allozyme variations):

  • Cannabis sativa
  • Cannabis indica
  • Cannabis ruderalis


Cannabis sativa
vs. Cannabis indica

While some experts believe that C. indica and C. sativa are different species belonging to the same genus, the way they classify these species is not how you might think.

In popular marijuana culture, cannabis plants with different phenotypes (appearances) and physiological effects have been categorized as either indicas, sativas, or hybrids (a cross between the two).

Sativas are widely believed to create an uplifting, mood-boosting effect when ingested, while indicas offer a calm, sedative feel. According to this theory, sativa plants are tall with narrow leaves and indica plants are short with broad leaves.

According to a genetic study on cannabis published in the journal PLOS ONE, this classification methodology is incorrect.

When the researchers compared the genetic structure of marijuana strains labeled sativa to those labeled indica, there was only a slight correlation. And even though strains labeled “indica” were more similar to one another genetically than to strains labeled “sativa,” this similarity didn’t align with the separate species C. indica and C. sativa.

Instead, they found that hemp plants and marijuana plants to be the true C. indica and C. sativa varieties. Meaning, hemp plants share more of their DNA with the evolutionary C. indica species or subspecies and marijuana plants share more of their DNA with the C. sativa species or subspecies.

The takeaway? Most marijuana that you encounter is primarily C. sativa, whether it’s labeled as an indica or a sativa. But keep in mind that there has been extensive cross-breeding over the years, so even marijuana plants have some C. indica within.

And experts still don’t agree as to whether C. sativa and C. indica are different species or different subspecies belonging to the same species. Today, experts usually consider all cannabis varieties belong to one species, Cannabis sativa.


Final thoughts: how should we classify cannabis?

Without a clear taxonomic classification for cannabis, the question that may come to mind is this: how should we classify different cannabis cultivars?

When it comes to the use of cannabis medicinally and recreationally, it’s most useful to classify cannabis by its chemical makeup, also referred to as its chemotype. The variation and concentration of cannabinoids and terpenes within tell us far more than any umbrella term like “indica” or “sativa.”

 

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