I Decline To Refer to Boswellia Carterii As B. Sacra (Flück), Here’s Why.
- Elizabeth Ashley: The Secret Healer
- Mar 13
- 13 min read
The Hidden Secrets of Hojari and B.Occulta
By Elizabeth Ashley
The species with the Latin name Boswellia carterii (Birdwood) is officially no more. It might sound like the apocalyptic cry of extinction of the resin—but thank goodness, it’s nothing of the sort. Instead, as aromatherapists, we are being asked to acknowledge the Latin name Boswellia Sacra (Flück), in its place. The AIA presented a tremendous webinar last week talking about the importance of remaining up to date with classification, and to be clear, I am heartily on board. Incorrect naming is confusing, misleading and has the potential to cause malpractice. But when I did a bit of digging into why Boswellia carterii was being rebranded, the nuts and bolts of its renaming gave me pause…I’m going to suggest that we should not be quite so hasty to kill off the species name Carterii just yet because the plant and essential oil are different and in this case botany and chemistry are actually in conflict with one another about what they have to say.
What Will Be Covered Here
For me to properly convey my argument I shall need to tell two separate stories.
First the botanical tale of the discovery of a new Frankincense species.
Then I need to explain some chemistry to show why the Boswellia sacra of Oman (known as Hojari Fusoos) is very different to the Boswellia sacra of Somaliland, not only because it is a co-distillation of two trees: the sacra tree and a newly discovered species Boswellia occulta, but also because of the way the environment it has grown in affects its stereochemistry...specifically with regards to alpha pinenes.
Once we are clear on that stereochemistry, I shall return to the first tale.
The first story is fascinating and it pertains to how the plant initially got named and why I agree that the term Boswellia carterii is now the wrong name for the species.
For ease, here are the chapters, if you would like to jump ahead.
Contents
Does The B.Sacra Tree of Oman create the same Essential Oil As the Boswellia Sacra Tree of Somalialand?
There are video explanations to all parts.
This one explains the whole thing, so you don't need to read if you don't want to. Otherwise I have also chopped it up and placed alongside the text sections.
This is part 1 of the sectional videos in the form of my introduction.
The History of Boswellia Carterii: Flückiger & Birdwood
The artist formerly known as carterii (see what I did there?) belongs to the frankincense tree now accepted as Boswellia sacra, which grows from northern Somalia across southern Yemen’s Hadramaut into Oman. Originally described as Boswellia sacra in 1867 by the Swiss pharmacognosist Friedrich August Flückiger in Lehrbuch der Pharmakognosie des Pflanzenreiches, it was only later that the name B. carterii was introduced for Somali material when in 1870, an English Botanist, Sir George Birdwood published a paper titled "On the Genus Boswellia," where he argued that trees he saw in Somalia were a species distinct from the trees of Boswellia sacra in Arabia.
In his paper, Birdwood described the Somali trees as being more robust, with differences in leaf and inflorescence form, and argued they merited species rank. So he named a “new” species Boswellia carterii after Henry John Carter, (H.J. Carter,) a surgeon-major in the East India Company who had collected significant specimens from both Arabia and Somalia.
Thus Boswellia carterii became known commercially as African Frankincense and Sacra was harvested from the Arabian peninsula, and it stayed that way for around 150 years until GC/MS reports became advanced enough to reveal something unusual about the Boswellia carterii oil. Sometimes it contained a constituent that shouldn’t be there. Not only should it not be there because it did not fit the frankincense profile, but actually it did not fit plants at all! This rare chemical had never previously been reported as a secondary metabolite from a plant, rather it was usually associated with microbes millipeds and even spider silks.
Methoxydecane: The Chemical Fingerprint of B. Occulta
Somali resin analysis showed that carterii resins exhibited massive amounts of decyl methyl ether (methoxydecane) and octyl methyl ether (methoxyoctane).
For a while, I think people suspected some kind of wrong doing, a kind of chemical adulteration. But then it seemed to validate that Birdwood must have been right. If the African tree made different chemicals, then it must be a different species. Then, eventually, a third possibility presented itself that perhaps a new chemotype had been discovered.
Dr. Prabodh Satyal of the Aromatic Plant Research Centre and Dr Robert Pappas of the Essential Oil University co-authored a paper titled: "First Reporting on the Chemistry and Biological Activity of a Novel Boswellia Chemotype: The Methoxy Alkane Frankincense." (Satyal 2016)
A new kind of frankincense….
How. Bloody. Exciting!
So, the search was on to find it!
Enter Anjanette DeCarlo
Dr. DeCarlo received her doctorate in Natural Resources and Environment from the University of Vermont. A director of the Save Frankincense initiative, she was Aromatic Plant Research Centre’s woman on the ground. In fieldwork in the Ceel Afweyn/Sanaag region, DeCarlo reported that harvesters distinguished between two different trees ‘Mohor cad’ (white mohor) and ‘Mohor madow’ (black mohor), then threw resins from both trees into collecting bags together. (Johnson, 2019) Together with a supply chain specialist Dr. Stephen Johnson, DeCarlo spent months collecting samples from the trees to isolate which did and which did not have methoxydecane.
Then they enlisted the help of Mats Thulin, a Swedish Professor of Organismal Biology from the University of Uppsala. Thulin’s specialism is systematics, phylogeny and biogeography of flowering plants. (Phylogeny studies how relationships between lines of descent among species or groups of organisms evolve. Biogeography studies distribution of species ecosystems, and biodiversity across the globe.) Thulin’s special focus is on plants that grow in the Horn of Africa.
The Discovery of the Hidden Tree “Occulta”
Mohor cad was accepted as the species recognised as Boswellia carterii, but what then was Mohor Madow? Species of this unusual tree was sent to Thulin to study. He detailed striking differences between the trees growing in the area. He argued that the classifications were wrong. There were two different trees here. The one that Birdwood had called carterii, and a species that had previously remained hidden from scientific analysis, which he called Boswellia occulta, and this new species was the source of methoxydecane and methoxyoctane being found in samples of carterii. (Thulin, 2019)
Further, Thulin then said Birdwood had been wrong though . White Mohor was not a distinct species. It was the same as that found in Arabia. It was sacra. Yes, Birdwood had been right that there was variation in appearance, but that was purely down to the trees adapting to their terrains. A tree growing on a rocky cliff in Somalia might evolve to look different to one in a sandy Omani wadi, but they are essentially the same body. Differences were down to terroir, not because they were different species.
As such then, he declared these carterii trees in Somaliland to be the same as the ones known as sacra in Arabia. Therefore Flückiger had been right all along.
He said they were sacra and they are, then this methoxydecane comes from this hidden tree, Occulta (Thulin, 2019)
So now comes the reclassification argument.
Superfluous Naming
Under the International Code of Nomenclature for algae, fungi, and plants (ICN) the rule is that the earliest classification stands.
Because Birdwood’s B. carterii does not represent a distinct species from Flückiger’s earlier B. sacra, the name B. carterii is now treated as an illegitimate later synonym under the ICN.
This is the taxonomy argument made by botanists about the tree.
And I am absolutely here for it.
I am happy to accept the reasons for the botanical change of the name.
However….
PART 2
Does The B.Sacra Tree of Oman create the same Essential Oil As the Boswellia Sacra Tree of Somalialand?
As my son would say to me, "What's the TL:DR mom, because this is very longwinded!"
The short answer is no....apart from the Boswellia carterii being a co-distillation of Boswellia sacra and B. occulta, even the two types of sacra essential oils are profoundly different because of their responses to the environment they grew in.
Chirality
To understand this argument, you need to know the word “enantiomers” which pertains to chemicals, but is best understood by thinking about your hands.
Usually, people have four fingers, a thumb and the palm of their hands and they have two of these.
So are the left hand and right hands the same?
No, they’re not. They are made up of the same components, but they are mirrors of each other.
You should understand enantiomers as being mirror forms.
Chirality speaks to the kind of handedness you have. Just as left hand gloves don't quite fit on right hands, and in the same way, you can’t superimpose an image onto a mirror.
In other words, if you have two enantiomers, then the chirality says they won’t act the same because some of the cells in our body can only react to right handed interactions and others prefer left handed ones.
Specifically in frankincense essential oil we are interested in Alpha pinene.
Alpha Pinene In Frankincense Essential Oil
Alpha Pinene is one of the most abundant constituents in frankincense essential oil and it has two enantiomers.
These are (+) - α-Pinene and (-) - α-Pinene
We’ll use the rather lazy commercial terms of “African Frankincense” and “Arabian Frankincense” for ease here…
The essential oils from African and Arabian Sacra are different in terms of the
Boswellia sacra (Omani/Yemeni): Has a high ratio of positive (+) enantiomers.
Boswellia carterii (Somali) : Has a much lower ratio (around 0.68), meaning it is predominantly negative (-). Woolley et al. (2013)
The reason this is important is that the enantiomers create a very different frankincense essential oils.
First: it affects the way the light shines through it
Omani sacra is dextrorotatory, which means light turns right when it shines through it. Somali sacra, by contrast is laevorotatory - it turns light to the left.
Second: It affects the aroma. An easier example for you to picture would be carvone. The (+)--carvone enantiomer in spearmint essential oil smells minty, but the reason caraway smells different is because of the (-) enantiomer.
How this plays out in the frankincense essential oils is that lower levels of the (-) enantiomer in the Somali Boswellia carterii give it its more traditional piney scent. In the Omani oil, the (+) - a - pinene presents as a fresh minty -turpentine aroma.
Enantiomers Affect Medicinal Properties of Frankincense Essential Oil
Consider these chemicals to be like keys, attempting to open locks, which are your receptors.. Even if the molecules look the same, the way they work is different, meaning that they might also also activate different receptors. A really scary example of when the pharmaceutical industry got this wrong was with the Thalidomide maternity drug. One "hand" of the molecule was a safe sedative but its mirror image was a potent teratogen which went on the affect thousands of children’s lives.
Essential oils are far more complex and generally safer, the principle remains: The body "reads" molecule’s shape, not just the chemical formula. And this is what we see with alpha pinene
A 2012 study (and reaffirmed in 2025) found that only the positive (+) enantiomers of Alpha-pinene showed significant microb icidal activity against Candida albicans and Staph. aureus. The negative (-) enantiomers—predominant in the Somali "Carterii" types—were often virtually inactive against those same pathogens in vitro.(da Silva Rivas 2012)
Research has shown that (-) - α-Pinene, (the laevorotatory form) has a much stronger spasmogenic effect on smooth muscle than the (+) - α-Pinene. (Yang, 2011)
While the (+) form wins on bacteria, some studies suggest the negative (-) enantiomers exhibit stronger antiviral effects, specifically against certain bronchitis-related viruses.(Yang, 2011)
A landmark study by Rufino et al. (2014) specifically looked at how different pinene isomers affect human chondrocytes (the cells that maintain your cartilage). They didn't just test "pinene"—they tested the specific mirror images.
(+)- α-Pinene, (Omani profile) was the most potent. It inhibited the inflammatory "master switches" (Nuclear Factor kappa B (NF-κB) and JNK) and stopped the production of catabolic enzymes (like MMP-1 and MMP-13) that eat away at the joint matrix.
They did test the negative enantiomer, (which would be the somali profile) and found it to be significantly less active. It did have some effect, but a far limper "handshake" that the positive enantiomer had with the chondrocyte's receptors.(Rufino, 2014)
Feature | Arabian B. sacra | Somali "Carterii" (B. sacra + B. occulta) |
Optical Rotation | Dextrorotatory (+) | Laevorotatory (-) |
Primary Enantiomer | (+) - α-Pinene | (-) - α-Pinene |
Key "Hidden" Marker | None | Methoxydecane |
Aroma Profile | Minty, Turpentine-sweet | Piney, Traditional Frankincense |
"Nomenclature follows the clinical and chemical distinctions... prioritizing stereochemical accuracy over botanical synonymy for therapeutic efficacy."
Nature Will Do Whatever She Pleases
Now in and of itself, this enantiomer aspect is not an argument for them being distinct species, as has been proposed by Woolley (2012). Vetiver, for example, does the same thing. It’s the environment in the heated north that means wild Khus creates an oil that is laevorotatory where the cultivated Ruh Khus shines right. (Ashley, 2015) That's plant intelligence at its best -to create new secondary metabolites to thrive - and indeed some plants are just really good at this. Helichrysum italicum, for example, a genius whose sole objective in life seems to be to stump the chemist. Its phytobiology changes almost from field to field. (Ashley, 2016)
But here’s the thing.
Boswellia sacra is a Near Threatened species. We require clarity in terminology to protect it. Omani sacra is under threat, where “carterii” - as it was previously known - is fairly stable. It’s all too easy to increase a population on paper by simply swallowing carterii as a species into sacra. In a collaborative paper, Johnson and DeCarlo relate that of the 24 species in the Boswellia genus, each has different circumstances and challenges to face. Hence, they need to be treated as an individual entity to protect them, rather than them being homogeneously lumped together as a multi-species entity. Their belief is that calling them by the same name (Botanical Synonymy) leads to treating them as if they have the same problem with a kind of regulatory blindness which ultimately fails the trees, the science, and the people.
So, I am Yet to Be Convinced I Need to Follow The Botanists
If I believed that all the essential oils coming out of Somalia were pure Boswellia sacra, I might be persuaded to change the naming, but the incentives are simply not in place to ensure it is.
B. occulta grows in the exact same regions (Sanaag region of Somaliland) as the carterii trees and B. frereana. Even to a trained eye, the trees can look similar when they aren't in leaf or flower. To a worker paid by weight, a resinous tree is a resinous tree. Harvesters often don't distinguish between the trees when collecting.
In several papers and presentations (including at the ISEO 2019 conference), Johnson noted that:"Essential oils being sold commercially as pure Boswellia carteri often turn out to contain methoxydecane, demonstrating the lack of traceability in the supply chain."
Boswellia sacra (Flück) is the name of the very highest quality Hojari resin from Oman. It is very much in the interest of essential oils companies to take on that name, but in reality how can you label what used to be carterii as the same? Not only do you label the Somali resin as something that it is not, but in doing so you devalue Hojari fusoos.
Aside from the quality and purity aspect, forcing the name sacra onto everything steals nuance about the oil we are buying. It loses the ability to distinguish the Omani Pure-Breed from the Somali Wild-Mix (the sacra/occulta blend) and so many energetics of the oil.
All that said, I am aware I am handing you a conundrum which could turn out to be a poison chalice of the future. So what do you do? Do you go with the flow, as expected by the journals and examining boards, or to join me over here with Suzanne Vega (Left of Centre, Off of the track) advocating for the rights of the plant, and actually for the rights of our clients too, because they have a right to as clear a vision as they can have about what is in their preparation.
So here are my…
Practitioner Steps for My Fellow Trouble Makers at the Back of the Bus
1. Continue using "carterii" for Somali oils to preserve chemical nuance (Woolley 2012). Since correct binomial nomenclature is an examined skill, ensure to add footnotes to essays and recipes to explain your deviation from what is currently deemed best practice. Feel free to link to “I Decline To Refer to Boswellia Carterii As B. Sacra (Fluck), Here’s Why.” (Ashley 2026)
2. Protect the integrity of arguably finer materials by labeling them as "Omani sacra” or "Hojari sacra" to protect premium grades.
3. Ask suppliers for single-species sourcing with GC-MS reports, not just botanical labels.
4. Look for methoxydecane (>1%)in GC/MS to detect occulta contamination (Johnson 2019),
To Conclude
I love taxonomy because each name has an amazing story behind it. I agree that binomial nomenclature should be clear, concise and accurate. However it should also speak to all aspects of the entity it serves. Botanists are not led by chemistry but aromatherapists fundamentally are. Similarly as an industry we pride ourselves in trying to be mindful of quality, so our own supply chain transparency is just as important. By retaining Boswellia carterii as a label we understand this is a co-distillation (we accept that for attars) derived from two species, one of which contains laevoratory compounds with a distinct profile from a tree that comes from Oman.
My dad used to say "If it looks like a duck and quacks like a duck, it must be a duck", but these two essential oils are not even close to being similar, and even if they were, (that Omani sacra were the same as Boswellia sacra from Somaliland, one also has this occulta resin in it.
It is so very very complex. So how on Earth do can we navigate this field. Well in these kinds of situations Occam's Razor seems appealing. In a world where all the fields conflict the simplest solution is usually the best. I say leave it alone but allow it to be the poster boy for best practice because best practice in therapy is more than one thing. Yes you can be a brilliant clinician with all the greatest knowledge in the world but of you cannot sell, then you have a problem. Telling the tale of carterii gives you opportunity to tell customers so much about sustainability issues, advanced pharmacokinetics, history, botany, olfaction…
Taxonomy serves botanists. Aromatherapists need chemistry, supply chain transparency, and conservation clarity pertaining to a plant that is one of humankind’s most special allies.
Works Cited
Johnson S, DeCarlo A, Satyal P, et al. (2019) “The Chemical Composition of Boswellia occulta Oleogum Resin Essential Oils” – Journal of Natural Products
Johnson S, DeCarlo A (2019) “Organic Certification is Not Enough: The Case of the Methoxydecane Frankincense”
Satyal P et al. (2016) “First Reporting on the Chemistry and Biological Activity of a Novel Boswellia Chemotype: The Methoxy Alkane Frankincense”
Thulin M, DeCarlo A, Johnson SP (2019) “Boswellia occulta (Burseraceae), a new species of frankincense tree from Somalia (Somaliland)” – Phytotaxa 394(3): 219–224
Wooley, C (2012) Chemical differentiation of Boswellia sacra and Boswellia carterii essential oils by gas chromatography and chiral gas chromatography–mass spectrometry - Journal of Chromatography
Camara, C. C., et al. (2003) "Antispasmodic effect of the essential oil of Plectranthus barbatus and some major constituents on the guinea-pig ileum" – Planta Medica
Rivas da Silva, A. C., et al. (2012) "Biological Activities of $\alpha$-Pinene and $\beta$-Pinene Enantiomers" – Molecules
Rufino, A. T., et al. (2014) "Anti-inflammatory and chondroprotective activity of $(+)-\alpha\text{-pinene}$: structural and enantiomeric selectivity" – Journal of Natural Products
Yang, Z., et al. (2011) "Comparative Anti-Infectious Bronchitis Virus (IBV) Activity of (-)-Pinene: Effect on Nucleocapsid (N) Protein" – Molecules
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