The Cannabis Family Tree – Cannabaceae and Phylogenetics
The sometimes-confusing world of taxonomy helps botanists to understand the phylogenetic journey of a plant. In this article, we explore the phylogeny (evolutionary relationships) of cannabis and its evolution into the Cannabaceae family. We talk about cannabis ancestors and close relatives, and other members of the Cannabaceae family.
The task of categorizing and cataloguing the billions of plant species that have existed on our planet since the dawn of life is a huge and vastly complex one. Prior to the development of genetic testing, classification on the basis of perceived similarity was the only way to assign a plant to its correct taxon.
Now that we have developed the study of phylogenetics (evolutionary relationships between groups of organisms), we have some basis for classifying plants according to their genetic similarities — but that does not provide a problem-free approach to such a complex task.
Cannabis within the cladistic system
However, we can at least begin to classify plants according to a cladistic system. The cladistic system relies on the presence of a single common ancestor. In this way, every clade (branch) of the phylogenetic tree contains the descendants of a single common ancestor. When many plants share a common ancestor, they are said to be monophyletic.
According to the Integrated Taxonomic Information System (ITIS), the species Cannabis sativa L. belongs to the genus Cannabis, which belongs to the Cannabaceae family. The Cannabaceae family, along with three other families, make up the (informal) suborder, Urticalean rosids, of the order Rosales. Along with the Urticalean rosids, another five families belong to the Rosales order; these include Rosaceae (rose) and Rhamnaceae (buckthorn).
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The complex and confusing world of plant taxonomy
The Rosales order belongs to the informal subclass (or superorder) Rosanae (or Rosidae), a huge clade that comprises almost one quarter of all flowering plants. These ‘rosids’ belong to the Magnoliopsida or Eudicot class, which is a member of the Angiospermae infradivision. In turn, these belong to the subdivision of Spermatophytina, of the division of Tracheophyta, of the infrakingdom Streptophyta or Embryophyta (land plants), of the Viridiplantae (green plant) subkingdom.
The Viridiplantae phylum consists of green algae as well as all land plants. Along with the phyla of Rhodophyta (red algae) and Glaucophytes (freshwater microalgae), it makes up the Archaeplastida kingdom, which is also known as Plantae sensu lato — meaning “plants in the broader sense”.
The issue of whether Archaeplastida is in fact a higher clade comprised of the kingdoms of Viridiplantae etc. is somewhat controversial.
Characteristics of the various taxa
Viridiplantae differ from other phyla in the Archaeplastida clade in that they produce both chlorophyll a and b, giving them their usual green colour; Rhodophyta and Glaucophytes produce just chlorophyll a.
Embryophyta comprise all land plants, and are believed to have diverged from green algae around 540 million years ago (Ma).
Tracheophyta, or vascular plants, contain fibrous tissue to conduct water and minerals, and include mosses and ferns as well as flowering plants. Spermatophytina are vascular plants that produce seeds, and are believed to have diverged from non-seed-bearing plants around 319 Ma.
Angiospermae are classified thus due to their shared characteristic of bearing seeds enclosed in protective structures; they all bear flowers, which later produce the seed-containing fruit, and appeared on the fossil record around 192 Ma. Eudicots are angiosperms that express two embryonic leaves, as opposed to monocots that produce just one. Eudicots also exhibit a characteristic three-grooved pattern on the pollen grain.
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The Rosidae superorder and the Rosaceae family
The Rosidae are believed to have appeared 108-121 Ma, and are usually characterised by their showy flowers—the Urticalean rosids are notable exceptions to this rule. Research has shown that the more recent evolutionary divergences have tended towards non-showiness, as wind-pollination became more prevalent. The Rosales order comprises a huge variety of evergreen and deciduous trees, shrubs, vines and herbs: for example, the Rosaceae family contains an incredible variety of important species including peach, apple, strawberry, almond, and of course rose.
The relatively recent Urticalean rosids
Thought to be relatively recent offshoots of the phylogenetic tree, the Urticalean rosids are characterised by their often non-showy and mostly unisexual flowers (although elm flowers are usually bisexual). As well as the Cannabaceae, the Urticales include the Urticaceae (nettle), Ulmaceae (elm), and Moraceae (mulberry or fig) families. Male flowers are inconspicuous and contain no petals, only sepals; female ovaries contain a single ovule, and produce a single seed.
Urticalean rosids exhibit huge variation in morphology and biogeography, and have developed some striking adaptations. Plants are usually wind-pollinated, although several Moraceae family members are insect-pollinated. Several species within the nettle family have the unique ability to explosively disperse pollen into the wind. Fruits may be hard, dry achenes, as in cannabis; fleshy drupes, as with hackberry; fleshy synconiums, unique to figs; or compound clusters as found in mulberry. Interestingly, several mulberry species are thought to contain mild hallucinogenic properties, and high-quality fibre can be obtained from the bark.
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The confusing classification of the Cannabaceae family
The 170 or so members of the Cannabaceae family have few characteristics that are distinct from the Urticales as a whole. DNA evidence has shown that all are related, and certainly humulus (hops) and cannabis share obvious similarities with regard to floral structure. Both contain terpenoids, accounting for their similar fragrance, but humulus is a vine (climbing plant) and cannabis is herbaceous. The Celtis (hackberry) genus is relatively dissimilar: Celtis species are usually tall deciduous trees, with simple leaves, unlike the compound palmate leaves found in humulus and cannabis. Celtis trees are usually not dioecious and although flowers are usually unisexual, they are found on the same plant.
Despite the many differences, the male flowers of many Celtis species bear a striking resemblance to those of cannabis. Other similarities between members of the Cannabaceae family include stipule-bearing leaves (in cannabis, the stipules are the two tiny shoots at the base of each leaf), and cystoliths, or enlarged leaf cells containing crystals of calcium carbonate.
Other noteworthy Cannabaceae plants
Although it is commonly believed that Cannabis and Humulus are the only two Cannabaceae genera with any commercial value, there are several other species that are of great value in the regions in which they are indigenous.
Various Celtis species are cultivated either for timber or as ornamentals, such as the protected South African tree, C. Africana. It’s attractive, fast-growing and frost- and drought-resistant. Its abundant flowers and small, sweet fruits also attract a variety of birds and insects to the garden.
C. sinensis from East Asia and C. australis from southern Europe are also widely cultivated for these purposes.
Trema orientalis, a common species distributed throughout the tropical and warm temperate regions of Africa, Asia and Oceania, has abundant uses. Many indigenous populations refer to it as the “charcoal tree”, as one of its uses is for charcoal production. Its wood burns quickly and easily, and is also useful for making paper and pulp, due to the high tensile strength of the fibres.
The fibres of the bark are used to make rope or twine, and the sap exuded can be used to waterproof fishing lines. It is also used as animal fodder. Interestingly, T. orientalis has various traditional medicinal uses, many of which are quite similar to those of Cannabis—it is used to treat dysentery, inflammation, sore throats, and asthma, among other things, and has shown promising results in preliminary trials as a blood-sugar stabiliser in diabetes.
Aphananthe aspera, an East Asian species also known as the Muku tree, is a highly-prized ornamental traditionally used in Chinese classical gardens. A. aspera is also useful as a source of fibre and wood, and its leaves are used as fine sandpaper for polishing wooden and similar objects. A particularly fine, seven-trunked A. aspera is listed as one of South Korea’s natural monuments; this sixteen-metre specimen is believed to be around three hundred years old.
Are cannabinoids unique to Cannabis?
The Cannabis genus is apparently unique within the Cannabaceae family for containing cannabinoids. There is evidence to suggest that cannabimimetics – cannabinoid-like compounds – are found in other plant species, particularly echinacea, which is a member of the Asterid subclass, and must therefore have evolved separately to cannabis for millions of years. This may imply that a proto-cannabinoid system existed in a common ancestor of both plants, prior to the divergence of the Rosid and Asterid clades around 126 Ma.
However, as far as current knowledge goes, no other plant species produces THC or CBD. These cannabinoids are specific to the cannabis plant. There are companies who claim to have produced CBD from sources such as limonene from citrus fruit, and the bark of evergreens from Southeast Asia, but as yet, no independent peer-reviewed science has emerged to verify these claims.
Given the great improbability of a new plant species containing a fully functional phytocannabinoid system suddenly springing into existence, gradual evolution of complex cannabinoid systems from more rudimentary lineages seems to be the only plausible explanation. Traces of early Cannabaceae species have been found in Cretaceous fossils dating from up to 93.5 Ma, but there is no concrete evidence as to when the Cannabis genus diverged.
The fact that no close living relatives of cannabis show evidence of a cannabinoid system is surprising, but as research continues, more cannabinoid-containing plants may be discovered. This may necessitate further reshuffling of the complex and confusing system of plant classification.What is the evolutionary story of cannabis? We explore this mystery through phylogenetics (evolutionary relationships) and the cannabis family tree.
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 21 st 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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