Cannabis is, for all practical purposes, the only plant that produces significant amounts of delta-9-tetrahydrocannabinol (THC). No other species in nature has been confirmed to accumulate THC at levels anywhere close to what cannabis achieves in its resinous flower clusters. That said, the broader world of “cannabinoid chemistry” extends well beyond a single genus. A handful of unrelated plants produce molecules that are structurally similar to THC or that interact with the same receptors in the human body, and at least one South African daisy relative assembles cannabinoid precursors through an entirely independent evolutionary pathway. The picture is more interesting and more complicated than a simple list of species.
How Cannabis Makes THC
THC does not appear in the cannabis plant ready-made. The plant first builds a precursor molecule called cannabigerolic acid, or CBGA, by combining two chemical building blocks from different metabolic pathways. CBGA is the shared starting material for all of the plant’s major cannabinoids. From there, a dedicated enzyme called THCA synthase converts CBGA into tetrahydrocannabinolic acid (THCA), the acidic form of THC that the living plant actually stockpiles.1PubMed Central. The biosynthesis of the cannabinoids Parallel enzymes shunt CBGA toward other endpoints: CBDA synthase produces cannabidiolic acid (the precursor to CBD), and yet another enzyme leads to cannabichromenic acid (CBCA).2Horticulture Research. Cannabis sativa: origin and history, glandular trichome development, and cannabinoid biosynthesis
The “active” THC that people associate with cannabis actually forms after harvest. THCA converts into THC through a simple heat-driven process called decarboxylation, which is why smoking, vaping, or baking cannabis releases the psychoactive compound. Fresh, living cannabis flower contains almost entirely THCA, not THC itself.2Horticulture Research. Cannabis sativa: origin and history, glandular trichome development, and cannabinoid biosynthesis
Where THC Lives Inside the Plant
If you have ever handled a cannabis flower and noticed it felt sticky, you were touching the structures responsible for THC production: glandular trichomes. These are tiny, mushroom-shaped outgrowths that cover the surface of female flowers and the small leaves (bracts) surrounding the developing seeds. Three types exist, termed bulbous, capitate-sessile, and capitate-stalked, with the latter two being the most productive. The capitate-stalked trichomes, with their large globular heads perched on tall multicellular stalks, develop later in the flowering cycle and are particularly abundant on bracts encasing the ovary.3American Journal of Botany. Morphology of Glandular Hairs of Cannabis sativa from Scanning Electron Microscopy
Detailed immunochemical mapping has shown that THC accumulates primarily in the cell walls and the secretory cavity of these trichome heads, not inside the cells themselves. The compound was detected in the outer wall of the disc cells, in the subcuticular wall and cuticle, and in the fibrillar matrix filling the secretory cavity. It was largely absent from the cytoplasm of those cells, suggesting the plant actively shuttles its cannabinoids outward into extracellular storage.4American Journal of Botany. Immunochemical localization of Tetrahydrocannabinol (THC) in Cryofixed Glandular Trichomes of Cannabis (Cannabaceae) Leaves, stems, and roots contain far lower amounts of THC, and seeds contain virtually none.
Why Cannabis Bothers Making Cannabinoids at All
Producing all that sticky resin is metabolically expensive, so the payoff must be significant. The leading explanation is defense. When a trichome ruptures, whether from an insect chewing on the flower or from high ambient temperatures, its contents form a viscous, glue-like coating on the plant surface. That gummy residue sticks to the mouthparts and legs of herbivores, discouraging further feeding. Cannabinoid production also ramps up under environmental stress: higher temperatures, low soil moisture, and poor mineral nutrition all correlate with increased cannabinoid output.5Trends in Plant Science. What Plants Contain THC? A Look at Cannabis and More – Section: Sites of Phytocannabinoid Biosynthesis and Their Possible Functional Roles Another proposed function is UV protection: the chemical structure of cannabinoids allows them to absorb destructive UV-B radiation, acting as a botanical sunscreen in the harsh, sun-drenched environments where cannabis likely evolved.
The Liverwort That Fooled Everyone
The most famous non-cannabis source of a THC-like molecule is Radula marginata, a tiny liverwort native to New Zealand and parts of Japan. Liverworts are small, low-growing plants that separated from the evolutionary line leading to modern seed plants hundreds of millions of years ago, so any chemical resemblance to cannabis is a case of convergent evolution rather than shared ancestry. Radula species produce a compound called perrottetinene (PET), a bibenzyl cannabinoid whose molecular structure looks strikingly similar to THC.6PubMed Central. Uncovering the psychoactivity of a cannabinoid from liverworts associated with a legal high Perrottetinenic acid, the acidic form, was first isolated from R. marginata alongside PET itself.7PubMed. New bibenzyl cannabinoid from the New Zealand liverwort Radula marginata
But PET is not THC. Its three-dimensional shape is actually a mirror image at a key position, and this matters for how it interacts with receptors in the brain. Computational modeling shows that PET and THC dock into the CB1 receptor in similar ways, but PET behaves as a partial agonist, activating the receptor more weakly and potentially with fewer side effects than THC.8PubMed. Shared Binding Mode of Perrottetinene and Tetrahydrocannabinol Diastereomers inside the CB1 Receptor May Incentivize Novel Medicinal Drug Design: Findings from an in Silico Assay This has attracted interest from researchers who see PET as a possible lead for drug development, not as a substitute recreational drug.
More recent chemical work on Radula marginata has uncovered additional cannabinoid-type compounds, including a previously uncharacterized molecule called perrottetinene diol (PTD), which is structurally analogous to CBD rather than THC. Researchers analyzing 75 collections from multiple New Zealand locations found that R. marginata displays distinct chemotypes dominated by either PET, PTD, or another bibenzyl compound, echoing the way different cannabis strains are dominated by THC or CBD.9PubMed Central. Unique bibenzyl cannabinoids in the liverwort Radula marginata: parallels with Cannabis chemistry The parallel is chemically fascinating, even though the underlying biosynthetic pathways in the liverwort are completely different from those in cannabis.
The South African Daisy That Makes Real Cannabinoids
The most surprising recent discovery in this field involves Helichrysum umbraculigerum, a woolly-looking member of the daisy family (Asteraceae) native to South Africa. In 2023, researchers reported that this plant produces genuine cannabis-type cannabinoids, including cannabigerolic acid at concentrations of about 4.3%. The biosynthetic route was confirmed through whole-genome sequencing, enzymatic assays, and pathway reconstruction in both tobacco plants and yeast. The enzymes involved are analogous in function to those in cannabis but evolved independently, making this a clear case of parallel evolution.10Nature Plants. Parallel evolution of cannabinoid biosynthesis The Helichrysum pathway also generates previously unknown cannabinoid metabolites, suggesting a more diverse chemical repertoire than what cannabis produces.11PubMed Central. Turning a new leaf on cannabinoids
Importantly, while Helichrysum produces the precursor CBGA and some downstream products, there is no evidence so far that it accumulates THC in meaningful amounts. The THCA synthase step that cannabis uses to convert CBGA into THCA does not appear to be replicated in the same way. So this is a plant that shares an early chapter of the cannabinoid story with cannabis but diverges before arriving at the compound most people care about.
Trema Micranthum and a Controversy
Trema micranthum, a tropical tree in the same botanical family as cannabis (Cannabaceae), has been the subject of conflicting reports. One study detected THC, CBD, CBDA, and THCA in its leaves, inflorescences, and fruits at low concentrations, with CBD in the fruits present at more than 100 times the THC level. The cannabinoids in the fresh plant material were found predominantly in their acidic forms, just as in cannabis.12Scientific Reports. Trema micranthum (L.) Blume as a new source of cannabinoids
However, a separate study using a different analytical approach found that initial positive screening results were not confirmed by more rigorous techniques. The researchers concluded the positive signals were likely caused by other phenolic compounds rather than true phytocannabinoids.13PubMed Central. Does Trema micranthum (L.) Blume Produce Cannabinoids? The disagreement has not been fully resolved. Analytical sensitivity matters enormously when trace-level cannabinoids are involved: one team’s “detected” can be another team’s noise. For now, Trema is best described as an intriguing lead rather than a confirmed secondary source of THC.
Plants That Do Not Contain THC but Act on the Same Receptors
A common source of confusion is the difference between a plant that contains THC (or a structural relative) and a plant that happens to produce compounds interacting with the body’s cannabinoid receptors. Your body has two main cannabinoid receptors, CB1 and CB2, and several plant-derived molecules bind to one or both without being structurally related to THC at all. These “cannabimimetic” compounds are widespread in the plant kingdom.
Echinacea
Echinacea, the herb widely sold as an immune booster, contains a class of fatty acid derivatives called alkylamides (sometimes spelled alkamides). These molecules show selective affinity for the CB2 receptor, with binding values in the low nanomolar range, while having much weaker affinity for CB1.14Journal of Biological Chemistry. Alkylamides from Echinacea Are a New Class of Cannabinomimetics: CANNABINOID TYPE 2 RECEPTOR-DEPENDENT AND -INDEPENDENT IMMUNOMODULATORY EFFECTS Because CB2 receptors are expressed mainly on immune cells rather than in the brain, echinacea’s alkylamides do not produce anything resembling a “high.” Instead, the CB2 interaction may help explain why echinacea preparations have immunomodulatory effects: the alkylamides appear to influence immune cell signaling in a concentration-dependent manner.15Frontiers in Pharmacology. Interactions of Echinacea spp. Root Extracts and Alkylamides With the Endocannabinoid System and Peripheral Inflammatory Pain The idea that your echinacea tea is “activating your cannabinoid system” sounds dramatic, but the practical effects are subtle and limited to immune modulation rather than psychoactive changes.
Acmella oleracea (The Toothache Plant)
Acmella oleracea, sometimes called the toothache plant or buzz button, is a tropical herb known for the intense tingling and numbing sensation it produces when you chew its flower heads. It also contains alkylamides, and molecular docking studies suggest these compounds interact with both CB1 and CB2 receptors as well as with TRPV1, a pain-sensing receptor.16PubMed. Alkylamides from Acmella oleracea: antinociceptive effect and molecular docking with cannabinoid and TRPV1 receptors The alkylamides appear to reduce pain perception in animal models without producing the classic side effects associated with THC, such as reduced movement or catalepsy. This makes Acmella an interesting candidate for pain-relieving agents that work through the endocannabinoid system without the baggage of psychoactivity.17PubMed. The potential of Acmella oleracea as a nutraceutical source for the symptomatic treatment of Burning Mouth Syndrome
Kava
Kava, the Pacific Island relaxation drink made from Piper methysticum root, contains a compound called yangonin that binds to the CB1 receptor with moderate affinity. Yangonin stands out among the kavalactones because it was the only one in a broad screen to show measurable displacement of a radioligand from the human CB1 receptor, and it showed selectivity over CB2.18Pharmacological Research. Kavalactones and the endocannabinoid system: The plant-derived yangonin is a novel CB1 receptor ligand Whether this CB1 activity meaningfully contributes to kava’s well-known sedative and anxiolytic properties alongside its other pharmacological actions remains an open question.
Black Pepper and Other Spice Plants
Beta-caryophyllene is a sesquiterpene found in the essential oils of black pepper, cloves, rosemary, hops, and cannabis itself. It selectively binds the CB2 receptor and functions as a genuine agonist: oral administration in mice reduced inflammation through a CB2-dependent mechanism, confirmed by the fact that the effect disappeared in mice lacking CB2 receptors. Researchers have called it a “dietary cannabinoid” because it is a normal, everyday component of the human diet.19PubMed Central. Beta-caryophyllene is a dietary cannabinoid The amounts present in a dash of black pepper are small, so this is more of a pharmacological curiosity than a practical source of cannabinoid receptor activation, but it neatly illustrates how widely distributed cannabinoid-active molecules are across the plant world.
Why THC Specifically Stays Rare
Given that compounds hitting cannabinoid receptors pop up in liverworts, daisies, coneflowers, and pepper grinders, it is worth asking why THC itself remains essentially unique to cannabis. Part of the answer is biochemical: the THCA synthase enzyme that converts CBGA into the direct THC precursor is highly specific. It belongs to a family of oxidoreductases, and the gene encoding it appears to have evolved under strong selection pressure within the Cannabis genus.1PubMed Central. The biosynthesis of the cannabinoids Other plants that produce CBGA, like Helichrysum, lack a corresponding enzyme to push the pathway all the way to THCA. The liverwort route to PET uses an entirely different chemical scaffold (bibenzyl rather than terpenophenolic), arriving at a molecule that looks similar to THC on paper but is built from different ingredients. Evolution converged on the receptor interaction, not on the molecule.
THC is also a potent CB1 partial agonist, meaning it directly activates the brain’s cannabinoid receptors. Most of the non-cannabis compounds discussed here are CB2-selective, which keeps them out of psychoactive territory.20PubMed Central. Phytocannabinoids beyond the Cannabis plant – do they exist? The pharmacological profile of THC, acting as a partial agonist at both CB1 and CB2 and producing the familiar euphoria, pain modulation, and appetite stimulation, is something cannabis achieves through a combination of the right molecule at a high enough concentration.21PubMed Central. The diverse CB1 and CB2 receptor pharmacology of three plant cannabinoids: delta9-tetrahydrocannabinol, cannabidiol and delta9-tetrahydrocannabivarin No other plant comes close to replicating that particular combination.
Engineering Cannabinoids Without Plants
The scarcity of THC outside cannabis has driven interest in producing cannabinoids synthetically. The most successful approach so far involves engineering brewer’s yeast (Saccharomyces cerevisiae) to carry the cannabis biosynthetic pathway. In 2019, researchers reported that genetically modified yeast could produce THCA, CBDA, and several other cannabinoids from the simple sugar galactose, essentially building the entire cannabis chemical assembly line inside a single-celled organism.22Nature. Complete biosynthesis of cannabinoids and their unnatural analogues in yeast The same system can generate cannabinoid variants that do not exist in nature, opening the door to pharmaceutical screening of novel compounds. Yields remain modest compared to what a cannabis plant produces per acre, but the approach avoids agricultural constraints like growing seasons, land use, and legal restrictions on cannabis cultivation.
The Helichrysum discovery also feeds into this biotechnology pipeline. Once researchers identified the enzymes Helichrysum uses to make CBGA independently of cannabis, they reconstructed parts of that pathway in both tobacco and yeast.10Nature Plants. Parallel evolution of cannabinoid biosynthesis Having two independent sets of biosynthetic tools from two unrelated plants gives engineers more options for building efficient production systems. Some of the Helichrysum tailoring enzymes generate cannabinoid metabolites that cannabis does not make at all, which could expand the range of compounds available for pharmaceutical research.
Common Misconceptions Worth Clearing Up
If you have spent any time in the herbal supplement aisle or on social media, you have likely seen claims that various “legal” plants are “natural sources of THC” or “contain cannabinoids just like marijuana.” A few corrections are in order. Echinacea does not contain THC or any structural cannabinoid; its alkylamides happen to bind a cannabinoid receptor, but they are chemically unrelated to anything in cannabis. The same applies to Acmella and black pepper. Calling them “cannabinoid plants” stretches the terminology past its useful meaning. A compound that binds a receptor is not the same as the compound the receptor was named after.
Radula liverwort has been marketed in some gray-market contexts as a “legal high” alternative to cannabis. While PET does engage CB1, its psychoactive potency is considerably lower than THC’s, and the amounts present in dried liverwort are small. The research interest in Radula is about drug design leads, not about recreational use. Anybody buying dried liverwort expecting a cannabis substitute is likely to be disappointed and may be exposing themselves to uncharacterized plant chemistry with unknown safety profiles.
Hemp-derived products add another layer of confusion. Hemp is simply cannabis bred to contain very low THC (below 0.3% by dry weight in the United States). It is the same species, Cannabis sativa, and it still produces the same suite of cannabinoids, just in different proportions. CBD products derived from hemp may contain trace THC, which is why some people test positive on drug screens after heavy use. The THC in those products comes from the cannabis plant, not from any alternative botanical source.
The Role of Microbes in Cannabis Cannabinoid Levels
One underappreciated factor in how much THC a cannabis plant ultimately contains is the community of microorganisms living inside it. Endophytic fungi and bacteria that colonize cannabis tissues can modulate the plant’s secondary metabolism, potentially influencing cannabinoid concentrations. Research into the cannabis microbiome has explored how these symbiotic or mutualistic relationships affect the production of compounds like THC and CBD.23PubMed Central. Cannabis Microbiome and the Role of Endophytes in Modulating the Production of Secondary Metabolites: An Overview This is still early-stage work, but it suggests that the THC content of a given cannabis plant is not determined solely by its genetics. Soil conditions, microbial inoculants, and growing practices all feed into the final chemical profile, which is one reason why two clones of the same cannabis strain grown in different environments can produce markedly different cannabinoid levels.