Summary
Foreword
Caveat. There are very few studies on the reproductive biology of the main Ocimum species – namely, on their reproductive processes (autogamy, allogamy, protandry, etc.) and their reproductive vectors (pollen, seeds, etc.). Not to mention the difficulty of navigating the various names, for example, of Ocimum americanum – x. citriodorum, basilicum x. citriodorum, africanum, canum – in order to determine whether the authors are referring to an ecotype of Ocimum americanum var. americanum or an ecotype of Ocimum americanum var. pilosum. Such a determination, therefore, requires delving into more conclusive characteristics: length of the stamens, length of the style, length and shape of the seeds, spaces between the verticils, number of chromosomes… if the study provides them.
Moreover, since the summer of 2022, I have had to carry out a real botanical, and genetic, detective investigation because the genetic resource center of the US Department of Agriculture – GRIN/USDA – has been distributing seeds of misidentified Ocimum ecotypes, around the world, for decades: seven ecotypes of Ocimum tenuiflorum which are Ocimum bisabolenum, numerous ecotypes of Ocimum basilicum which are Ocimum americanum var. pilosum, one ecotype of Ocimum americanum which is Ocimum kilimandsharicum, etc.
This essay, on the floral and reproductive biology of the main species of Basil, was inspired by my discoveries in the summer of 2025: strict allogamy in Ocimum kilimandscharicum, predominant allogamy in Ocimum selloi and Ocimum americanum var. americanum, numerous natural hybrids involving Ocimum kilimandscharicum and fewer involving Ocimum bisabolenum, etc.
These discoveries were made possible by the use of three insect-proof breeding tents, under strict self-pollination conditions, for the production of pure seeds and the study of the reproductive biology of each Ocimum species.
For 2026, I propose to continue my research based on this technique – for example, to evaluate the level of self-sterility or self-fertility of various ecotypes of Ocimum americanum var. americanum, Ocimum americanum var. pilosum, Ocimum carnosum/selloi, Ocimum campechianum, etc. I also wish to introduce pollinating bumblebee hives into these tents – if I can find them easily on the market – in order to assess the level of potential hybridization between various species: for example, between Ocimum kilimandsharicum and a purple cultivar of Ocimum basilicum; between a Citral ecotype of Ocimum americanum var. pilosum and Ocimum bisabolenum; between a Citral ecotype of Ocimum americanum var. pilosum and Ocimum kilimandsharicum; between a Cinnamon ecotype of Ocimum basilicum and Ocimum bisabolenum; etc.
On this subject, if I may offer some advice to gardeners wishing to create their own Basil hybrids based on criteria such as beauty, cold resistance, extreme floribundity, attractiveness to pollinators, exquisite fragrance, etc.: get your green fingers – and seeds – started with the species Ocimum kilimandscharicum as the parent plant.
An interspecific hybrid is a chimera that can be functional in terms of its development, the creation of new chemotypes and scents, its ability to reproduce by cuttings, etc. A chimera can also be sterile or fertile, producing viable seeds… or non-viable ones.
Recipe: Grow a few Ocimum kilimandscharicum plants and a larger number of Ocimum basilicum and Ocimum americanum var. pilosum plants (depending on the size of the garden) in small pots, sowing in February or March (depending on the region). When transplanting into the ground, once the risk of frost has passed, isolate one or more Ocimum kilimandscharicum plants (depending on the size of the garden) among other Ocimum basilicum and Ocimum americanum var. pilosum plants. The vast majority of Ocimum kilimandscharicum flowers – a species that is nearly 100% self-sterile – will be pollinated by pollen from the varieties, or ecotypes, of the other two species. All fertile seeds from Ocimum kilimandscharicum mother plants will produce plants with a huge range of corolla colors, pollen and anther colors, various scents, types of branching, flower stem lengths, etc.
In fact, the simplest thing to do at the very beginning – for quick and convincing results – is to select varieties of Ocimum basilicum with purple leaves or a cinnamon scent, and varieties of Ocimum americanum pilosum with Citral.
Thus, what is marketed on the perennial ornamental plant market as “Magic Mountain”, “Magic White” et autres “African Blue” – completely sterile lines – you can generate them yourself in your garden… for the pleasure of Evolution, with Design, and its Genetic Flows. While asking Mother Earth to generously grant you, one day, a line with fertile seeds!
I am convinced that we have not yet seen the last of the surprises involving Ocimum kilimandscharicum as the parent plant in hybrid plants. For example, when in the fall of 2024, I noticed that my first hybrid (1.5 meters wide and rooted in a compacted soil) of Ocimum kilimandscharicum, crossed with X, and with orange pollen, had branches with white flowers as well as branches with purple flowers.(Lien), I told myself that I had not paid enough attention, during the summer, to this extremely unusual phenomenon – which, to my knowledge, has not been documented to date – in a Basil.
Unfortunately, this plant did not survive its extraction, in December, and the only cutting we were able to save grew into a magnificent plant, 1.5 meters in diameter, during the summer of 2025… but only with branches bearing white flowers – as if this cutting did not carry the complete “chimeric” genetic information of the mother plant. But what a surprise it was, in October 2025, to discover that this plant was beginning to produce, in its lower part, branches with the same purple flowers as the mother plant – but in the minority. That is when I remembered that it seemed to me that this cutting had produced both colors in March – with the purple color suddenly disappearing. What should we conclude from this? Is there a “chimeric genetic” trigger which controls the color of the flowers on a particular branch? What do geneticists say?
While waiting for next spring, I have just overwintered a Besobila plant, as well as three Kapura plants, all hybrids, in our very sunny bathtub – which we never use because we live in a region with little rainfall. I selected these few plants from among fifty or so spontaneous crosses, of Besobila and Kapura, which will remain in the garden, or on the balcony, throughout the winter, to test their resistance to often violent winds and low temperatures of around -7°C.
And now back to one of my favorite topics: Ethiopian Besobila! Given the existence – not yet recognized by self-proclaimed botanical authorities – of Ocimum bisabolenum, I invite interested readers to refer to my various monographs, in three languages, on this species, which has a scent of myrrh and vanilla, which grows in Ethiopia at altitudes of up to 2,800 meters, is resistant to temperatures as low as -7°C, and contains Bisabolene, Estragole, Eucalyptol, and Eugenol as the major components of its chemotype. In particular, I invite them to refer to the section entitled “According to the paradigm of the genetic mythos… the Ethiopian Besobila is a true species: Ocimum bisabolenum,” in my latest monograph on the subject (Link), which I am repeating in part in this presentation in order to reiterate, once again, that Ocimum bisabolenum constitutes a true species in its own right.
“How can Ocimum bisabolenum and Ocimum americanum be distinguished specifically by the morphology of their flower stems?” Link.
“What the Fake is Going on in the Ocimum world? A Manifesto in Homage to the Ethiopian Besobila, Ocimum bisabolenum”. Link.
“Ethiopia is the source of the temperate Tulsi with its spicy scent of vanilla and myrrh… and red pollen – Ocimum bisabolenum”. Link.
“Un Manifeste en Hommage au Besobila Ethiopien, Ocimum bisabolenum… et une plongée, vertigineuse, au coeur du marasme botanique sévissant, chez les Basilics, depuis une cinquantaine d’années”. Link.
“Les propriétés anti-oxydantes et anti-cancérigènes de la Tulsi Ethiopienne, Ocimum bisabolenum”. Link.
“L’Ethiopie est la source de la Tulsi tempérée au parfum épicé de vanille et de myrrhe… et au pollen rouge – Ocimum bisabolenum”. Link.
“Un Manifiestó en Homenaje al Besobila de Etiopía, Ocimum bisabolenum, una Planta Medicinal Maestra”. Link.
In accordance with the current international taxonomic nomenclature, I propose to name the Besobila native to Ethiopia: “Ocimum bisabolenum Guillet Xochi, 2022”.
By the way, in 2014, at the foot of Mount Shasta in California, I discovered a new subspecies of Eriogonum microthecum, a wild buckwheat, which bears my name. The great botanist James Reveal, the expert on the Polygonaceae family in the USA, named it: “Eriogonum microthecum var. cyclophyllum. Guillet. Reveal. 2014”. Link. See my botanical website “Eriogoneae.com” presenting 154 species and sub-species of Eriogoneae.
In 2010, I had, already, discovered a new subspecies of Eriogonum umbellatum on Mount Adams in Washington State, which James Reveal was never able to investigate, in situ, because he died at the age of 72, at Cornell University, before we could complete a very large encyclopedic book, on the genus Eriogonum, with text from his immense manual and my high-definition photographs. I named it “Eriogonum umbellatum var. klickitatii”, because Mount Adams was known by Native American tribes as Pahto or Klickitat.
That not being said for the sake of self-satisfaction in my areas of gratification – to borrow an expression from the famous researcher Henri Laborit! – but to highlight that, nowadays, a PhD is not always a mark of authenticity, morality, or aptitude… This is especially true in the well-framed and censored “framework” of the Great Lottery of Neo-Darwinism… which takes its Messiahs for Lanterns (a pun with the French expression “prendre des vessies pour des lanternes”) by promoting the lottery of blind, random, and Designless Evolution.
Indeed, having never been interested in degrees or university courses (at 18, I only lasted three months at the Higher Institute of Theology and Philosophy in Nantes… due to early metaphysical dissent and early telluric descent into the heart of Serotonergic Neurognostics of the Gaian Biosphere), I don’t walk around with a PhD slung over my shoulder as a pledge of rootedness in the Real World!
That is why, out of the hundreds of emails I’ve sent since 2016 – as a taxonomist whistleblower with an Ocimum tune! – I’ve received very few replies… because I don’t have a degree.
Recently, a geneticist from Ethiopia told me, squarely, that she would not read my monographs on Ocimum on the grounds that I had not “published” anything… and, above all, because I questioned her recent study, which, genetically, lumped together, as best it could, 62 Ethiopian accessions of Basil in the species Ocimum basilicum, even though 57 of them are Ocimum bisabolenum with a Bisabolene chemotype. Link
I did not “publish” anything – peer reviewed, bla bla bla – but, nonetheless, I published, in French, so far, 18 monographs, or reports, on the Ocimum genus and more than 80 monographs on Master Medicinal Plants from Chinese, Indian, Native American, African, and other Pharmacopoeias. I could have narrate, to this Ethiopian geneticist, the little story – on the Abyssinian highlands with the intoxicating scents of Besobila – of the encounter between a bare-foot illumined Master and a well-groomed and well-educastrated neo-darwinist scientist…
That is why, despite the plethoric number of emails sent since the summer of 2022 to researchers and authors in the Ocimum sphere – regarding 113 studies, to date, that should be corrected or retracted – I have received very few responses because I do not have a degree and because I have never “published.” But also, and above all, because none of these researchers have any desire to correct – or worse, to retract – a study that has been funded, by generous sponsors, or universities, and “published” in prestigious scientific journals.
Ocimum bisabolenum
Description
The flower stems are, on average, 10 to 12 cm long and can reach 18 cm in well-watered plants.
According to the 2016 study, “A comparative study of morphological and anatomical structures of four Ocimum species in Uttarakhan. India” – which must be corrected or retracted because the authors analyzed an ecotype of Ocimum bisabolenum, incorrectly identifying it as Ocimum viride/gratissimum: «The young stem is quadrangular in outline. Outermost layer is epidermis (EP) composed of tangentially elongated isodiametric cells and covered by their cuticle. Hypodermis is slightly collenchymatous (Coll). Cortex (Co) is parenchymatous with air spaces.
Stele has four vascular bundles between them. Vascular bundles are collateral and open. Xylem (Xy) is without fibre tracheid with libriform fibres. Pith (M) in centre consists of lignified parenchymatous cells. Pith in the centre consists of lignified parenchymatous cells».
In addition, the authors mention that the average leaf area of a plant was calculated at 3,844 cm², which is five times more than the other three species studied: Ocimum basilicum (Thai), Ocimum tenuiflorum et Ocimum gratissimum. Link.
The interval between the (pseudo) whorls (or verticiles) is very small. Thus, there are 21 verticiles on an 18 cm flower stem – with an average interval of 8.5 mm.
It should be noted that the Ethiopian Besobila, Ocimum bisabolenum, is the only one, of the main species of Basil, that is characterized, in a minority of plants, by cristations/fasciations of the main stem, which can reach 10 cm in length – and nearly 1 cm in width. This fasciated main stem subsequently divides into two or three branches.
The bracts (approximately 3.5 mm long) are green, or dark green, with purple margins.
The flowers are purple, with a paler lower lip in some ecotypes. The inside of their corolla, 6 to 7 mm long, is completely hairless.
The flower peduncles are approximately 2.5 mm long.
Ocimum bisabolenum is thus the only major species of Basil with dark monochrome flowers: the corolla, stamens, and pistil are purple or violet in color.
In fact, this is why, in the 1980s, one of the ecotypes of Ocimum bisabolenum was marketed in North America under the name “Blue Spice.” This name referred to its bluish aura, which embellishes it in the middle of the day when its flowers are in full bloom, as well as its myrrh scent.
The calyxes (approximately 5 mm long) are purple on the outside – for most ecotypes – and green on the inside. The width of their shield is approximately 4 mm. In terms of hairiness, their upper lip (the shield) is almost hairless on the outer surface, while the lower lip is densely hairy on the inner surface.
The pistil is purple in color, turning white at its tip toward the white stigma. When mature, the four stamens extend well beyond the corolla: their filaments are purplish in color and their anthers are orange.
The pollen is orange/brick red in color. Its grains are oblong and 40% octacolpate, 30% heptacolpate, and 30% hexacolpate. They are approximately 55 microns in diameter. Link
In pollen grains, the number of grooves (colpi) and the nature of their pores allow the various species to be distinguished.
A: an A5 trichome with a brown content in the head; B: detail of a D3 trichome; C: an A2 trichome and an elongated E4 trichome positive to TBO; D: J: short sized element, positive to Fluorol Yellow 088, showing a terpenoid/lipidic content. Characterization of the floral traits, pollen micromorphology and DNA barcoding of the edible flowers from three basil taxa (Lamiaceae)
Ocimum bisabolenum is, thus, the only major species of Basil with three types of pollen grains: octacolpate, heptacolpate, and hexacolpate.
The seeds are black and oval to elliptical in shape, approximately 1.5 mm long. The weight of 1,000 seeds is approximately 0.5 to 0.6 grams. There does not appear to be any dormancy in Ocimum bisabolenum seeds.
Seed production is abundant and rapid. In fact, of all the major Ocimum species, Ocimum bisabolenum is the earliest to flower and bear ripe seeds.
Reproductive Biology
The single Ocimum bisabolenum plant that I grew during the summer of 2025, under controlled pollination conditions (isolated in an insect-proof tent), produced a normal amount of seeds.
Ocimum bisabolenum is, thus, a primarily self-fertile species.
Nevertheless, it appears that Ocimum bisabolenum also has a certain propensity to flirt – that is, to crossbreed with other Ocimum species.
Indeed, according to some photographs I took, it appears that certain flowers unfurl their stamens at the beginning of anthesis without their pollen being mature, which is very unusual in Ocimum bisabolenum. This process, thus, promotes intraspecific and interspecific cross-pollination.
Historically, as I explained for Ocimum kilimandscharicum, for around thirty years, in the European and North American organic seed production sphere, we have followed the principle of self-fertility and non-interspecific hybridization in the major Ocimum species, as well as the principles of validated intraspecific hybridization in Ocimum basilicum and Ocimum americanum.
We were clearly very wrong in the case of Ocimum kilimandscharicum and only slightly wrong in the case of Ocimum bisabolenum – since the capacity for inter-species crossbreeding in Ocimum bisabolenum is not comparable to that of Ocimum kilimandscharicum.
In fact, in September, when I noticed on a 72-cell tray, sown in August, that a number of Ocimum bisabolenum seedlings looked more like Ocimum basilicum, I thought that the wind, which is very strong in our region, might have played a trick on me like Coyote does – since I am surrounded with seeds from a wide variety of Basil plants.
For this first tray sown in August, I had selected seeds from six very large potted plants of Ocimum bisabolenum, which had grown during the summer on our balcony, surrounded by various species: Ocimum kilimandscharicum, Ocimum americanum americanum (ecotypes with camphor), Ocimum americanum pilosum (“Esfahan”), Ocimum basilicum (“Anis”, “Licorice” and “Cinnamon” – from Association Kokopelli).
So, I transplanted 60 plants from this tray into small pots – out of hundreds of seedlings that had sprouted – giving priority to those that definitely did not appear normal… at least from the Besobila’s point of view! These were 5 seedlings with leaves much larger than those of Besobila. But at the beginning of flowering, three other plants turned out to be hybrids, bringing the total to 8 Besobila hybrids.
Plagued by “scientific” doubt – because foreign seeds could have found their way into my open bag of potting soil, etc. – I have since replanted two trays of Ocimum bisabolenum seeds… with a new bag of potting soil. However, for these two new trays, I harvested seeds from a wide variety of plants in the garden. From these two trays, I transplanted about fifty seedlings and, by mid-October, I had already discovered several cross-pollinated plants.
On October 5, the first of eight abnormal plants bloomed: with large white flowers, a purplish pistil, and pale orange anthers lacking pollen at the beginning of anthesis. Over the following days, the other plants bloomed with white or pale mauve flowers, cream to pale orange anthers, and pollen in various shades of pale orange – sometimes mature at the beginning of anthesis.
Indeed, with some Besobila hybrids, the pollen only matures later – as with Ocimum kilimandscharicum.
In all of these plants – which are much taller than normal – the flowers are much larger than those of Ocimum bisabolenum. In some, the calyxes are not entirely purple but green and purple.
In addition, two of these plants are characterized by extremely broad, slightly ruffled leaves – of the type “Napoletano” ou “Lettuce” – with leaves 16 cm long (with a 4 cm petiole) and 9.5 cm wide.
Some of these spontaneous crosses are characterized by very long flower stems, whereas this is not the case for either the parent plant, Ocimum bisabolenum (with an average of 12 cm), or the pollen donor, which in this case is likely to be an Italian lettuce-leaf type.
It should be noted that in 1974, botanist Helen H. Darrah reported the existence of spontaneous crosses between Ocimum sanctum/tenuiflorum and Ocimum basilicum Link – which is frankly impossible, of course, as these species belong to two completely different groups of Ocimum. In reality, these were ecotypes of Ocimum bisabolenum, which she, then, named “Spice Basil. Ocimum sanctum” in her essay “Investigation of the Cultivars of the Basils (Ocimum)” published in the New York Botanical Garden Press. She described its “lavender-colored corollas and orange stamens” and mentioned that it was widely cultivated in the United States under this name. Helen Darrah further specified that she knew of three identical ecotypes of “Spice Basil. Ocimum sanctum”. According to the Division of Tobacco in Ames, Iowa, one came from the West Indies, namely ecotype GRIN PI 414204; the second came from the Maldives, via the Botanical Garden of Copenhague, in Denmark, (called Ocimum carnosum), namely ecotype PI 652056; and the third came from France (called Ocimum canum).
Thus, the existence of spontaneous crosses, between Ocimum bisabolenum and Ocimum basilicum, was mentioned as early as 1974… but this discovery remained confidential for half a century!
It should, also, be noted that Helen H. Darrah mentioned that the Spice Basil was strictly the only species of Basil that reseeded itself spontaneously in her garden: she even pulled it up before the plants came to flower. I can, indeed, attest to Besobila’s incredible propensity to reseed itself spontaneously in the garden, in flower-pots… and even in alleys of rocks.
Genetic Analyses
I invite the readers interested in the genetic analyses validating the species nature of Besobila – which I named Ocimum bisabolenum in 2022 – to refer to the section entitled “According to the paradigm of the genetic mythos… the Ethiopian Besobila is a true species: Ocimum bisabolenum,” in my latest monograph on the subject. Link.
1. According to the 2011 study by Klaudija Carović-Stanko et al. from the University of Zagreb, “Molecular and chemical characterization of the most widespread Ocimum species”, the 4 ecotypes of Ocimum bisabolenum that she analyzed – believing them to be 4 ecotypes of Ocimum tenuiflorum – occupied distinct positions from the rest of the species, on the phenetic trees, in terms of AFLP (amplified fragment length polymorphism) analyses, just like the accessions of Ocimum gratissimum.
It was also in this study – involving four ecotypes of Ocimum bisabolenum – that Klaudija Carović-Stanko discovered, in her analyses of essential oils, the usual components of the classic Besobila chemotype: Bisabolene, Eucalyptol, Estragole, and Eugenol. She also points out that, in terms of biochemical average, the greatest dissimilarity was observed between Ocimum africanum accessions (1.313), followed by Ocimum gratissimum (1.302), Ocimum basilicum (1.066), Ocimum americanum (0.630) and Ocimum bisabolenum (0.493) – meaning that the ecotypes of Ocimum bisabolenum are very similar.
Caveat. Not only is there a major error in this study concerning four ecotypes of Ocimum bisabolenum, but it should be noted that the three ecotypes of Ocimum americanum are, more precisely, ecotypes of the Citral chemotype of Ocimum americanum pilosum – as well as the accession 11, named Ocimum africanum, which is placed in the same clade.
Klaudija Carovic made it very clear that there were inconsistencies in the results of her analyses: «In the NJ tree and MP tree, two incongruences, concerning the O. basilicum ‘Erevanskii’ (06) accession and O. kilimandscharicum (17) accession, could be noted… On the MP tree, Ocimum kilimandscharicum was grouped with the ecotypes of Ocimum tenuiflorum as a sister taxon.» Link
Thus, according to Klaudija Carovic’s conclusions, the four ecotypes of Ocimum bisabolenum analyzed are, genetically speaking, the closest to Ocimum kilimandscharicum. Furthermore, she points out that the Dice distance between pairs of accessions belonging to the same species was high for accessions belonging to Ocimum gratissimum (0.744), but low for accessions belonging to Ocimum bisabolenum (0.233). See the diagram below. I have, in fact, stated on several occasions that there are not many genetic differences between the various ecotypes of Ocimum bisabolenum distributed by GRIN/USDA or marketed in the seed business.
2. According to the 2016 Polish study, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the ADN content of 3 GRIN/USDA accessions of Ocimum bisabolenum – PI 652059, PI 652056 et PI 414205 identified as Ocimum sanctum in the study – varies between 4372 Mbp and 4489 Mbp (around 4.5 pg/2C). Link.
3. According to the Israeli study from 2010, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, the DNA content of the Ocimum bisabolenum PI 652059 ecotype (from the Maldives) is 2,843 Mbp (approximately 2.91 pg/2C). Lien.
It should be noted that, according to this study—the first of its kind—all DNA content values for the various Ocimum species are somewhat lower than those proposed by the subsequent 2016 study in Poland.
4. The Italian study (published in September 2024), “Characterization of the floral traits, pollen micromorphology and DNA barcoding of the edible flowers from three basil taxa (Lamiaceae)”, has performed the genetic analysis of 3 accessions: “Blue Spice” (Ocimum bisabolenum), “Cinnamon” (Ocimum basilicum) and a Lemon cultivar of Ocimum americanum var. pilosum. Link
They submitted their results to the Genbank database – along with the declared taxa, origin, year of collection, and accession numbers. Blue Spice, an ecotype of Ocimum bisabolenum: 354 bp. Link.
5. According to the 2013 Taiwanese study, “Genetic diversity among Ocimum species based on ISSR, RAPD and SRAP markers”, the ecotypes “Spice” and “Blue Spice” constitute their own separated cluster – meaning their own species. Lien
Moreover, this Taiwanese study clearly affirmed that there was no difference between the ecotypes “Spice” and “Blue Spice”. Today, the Canadian seed company, Richters Herbs, which previously marketed both, now only markets “Spice”. Link
6. According to the 2018 study, “Population structure, genetic diversity and downy mildew resistance among Ocimum species germplasm”: Link « The k3.1 cluster includes 7 phenotypically indistinguishable accessions sourced from commercial seed companies and the USDA-GRIN. This cluster is highly supported (1.00) and evidently an autonomous population».
And what are the 7 accessions making up this “autonomous population”: “Blue Spice”, “Blue Spice F1”, “Spice”, PI 414204, PI 414205, PI 652056, PI 652059 – namely ecotypes of Ocimum bisabolenum. And, this, in addition to the ecotypes PI 414201 and PI 414203 which are included in the clade. Link
7. In Ethiopia, in June 2024, researcher Aynalem Gebre Gossa – from the Ethiopian Institute of Agricultural Research – published a new study on the genetic analysis of 62 Ethiopian Basil ecotypes mistakenly considered as all belonging to the species Ocimum basilicum. “Genetic diversity and population structure of Ethiopian basil (Ocimum basilicum L.) accessions using DArTseq markers.” The 62 basil accessions were divided into two genetic groups according to STRUCTURE analysis, unweighted pair group method (UPGMA), discriminant analysis of principal components (DAPC), and principal coordinate analysis (PCoA). According to the authors’ conclusions, «structural analysis uncovered the existence of two ancestral populations within the basil accessions, which was confirmed by clustering». Link
And why is that? Because they are, in fact, two different species… and ancestral! In fact, out of 62 accessions, 5 belong to one genetic group, which I identify as Ocimum basilicum var. thyrsiflorum (“Ajuban” or “Ashkuti”), and 57 to another genetic group – which is clearly Ocimum bisabolenum.
Aynalem Gebre Gossa never replied to my letter of August 2022, in which I proved to him that, according to his study of 2023, if 44 of its 49 ecotypes of Ethiopian Basils had considerable levels of Bisabolene, it was because they were not ecotypes of Ocimum basilicum var. thyrsiflorum but, rather, of Ocimum bisabolenum. According to this researcher: β-bisabolene was the dominant compound in almost all the accessions analyzed, except in five accessions (OB033, OB036, OB013, OB048 and OB047). Link
In conclusion, Ocimum bisabolenum is a mainly self-fertile species with, nevertheless, a slight propensity for interspecific cross-pollination.
Ocimum basilicum
Description
The length of flower stems varies considerably depending on the ecotypes and, more specifically, the subspecies of Ocimum basilicum. For example, it is twice as long in ecotypes originating in Asia – “Cinnamon”, “Thai”, etc – compared to varieties originating from Italian types known as “Genovese”.
The interval between the (pseudo) whorls, or verticiles, (composed of 6 flowers) varies from 9 mm to 16 mm, with an average of 12.5 mm.
The bract is between 6.5 and 14 mm long.
The calyx is 5 to 8 mm long.
The flower stalk is 2.5 mm to 6 mm long.
The corolla is generally more than 8 mm and up to 15 mm long.
Pollen grains are hexacolpate and measure approximately 53 to 75 microns in diameter, depending on the ecotype. Lien.
The seeds are ovoid to oblong to elliptical in shape. They can be black or blackish brown or reddish brown in color. According to Campion-Bourget et al. Lien, they are 1.9 to 2.4 mm long and 1.25 to 1.4 mm wide, with a thickness of 1.1 mm. Generally, the ornamentation of the epicarp is reticulate-foveolate (cells with edges forming a more or less regular network). The abaxial surface is often marked by an angular median ridge.
According to a study analyzing an ecotype of Ocimum basilicum thyrsiflora, the seeds are a rich source of lipids (33%) and carbohydrates (43%). They contain polyphenols, alkaloids, flavonoids, saponins, and triterpenoids. It is worth noting the predominance of α-linolenic acid in their oil. Link.
When moistened, they produce an abundant whitish mucilage. It should be noted that a number of studies have examined its dietary and medicinal uses, due to its quasi-hydrogel nature.
“Preparation, characterization, and biological evaluation of Ocimum basilicum hemicellulose-based composites for wound healing”. Link. “Structure, mechanical and adhesive properties of the cellulosic mucilage in Ocimum basilicum seeds”. Link. “Functional characterization of basil (Ocimum basilicum L.) seed mucilage”. Link. “Multilayered mucoadhesive hydrogel films based on Ocimum basilicum seed mucilage/thiolated alginate/dopamine-modified hyaluronic acid and PDA coating for sublingual administration of nystatin”. Link. etc.
The weight of 1,000 seeds is approximately 1 g to 2.2 g. Their dormancy at harvest is 75% and requires approximately 2 months to be completely broken. This dormancy is gradually broken after 3 weeks.
This summer, I was able to verify that sowing freshly harvested seeds of a Cinnamon cultivar variety yielded only two seedlings.
and abaxial face (x 50) ; 2, reticulate-foveate pattern of pericarp (x 300) ; 4, enlarged portion showing wax deposits on pericarp surface (x 5000). Lien
Reproductive Biology
According to the 2016 study, from Nigeria, “Comparative reproduction mechanisms of three species of Ocimum L. (Lamiaceae)”. One ecotype of Ocimum basilicum (B1) is considered to be 70% self-fertile, while the other ecotype of Ocimum basilicum (B2) is more than 80% self-sterile. It is considered to be a hexaploid, with 2n = 72. Link – which is rare in Ocimum basilicum but has, nevertheless, been mentioned in the 2005 study, “Secondary Chromosome Associations in Ocimum basilicum L. and Ocimum tenuiflorum L”. Link
Unfortunately, there are currently almost no published studies on the reproductive biology of the species Ocimum basilicum. There is a very old study from 1997, from Kerala, which indicates a self-sterility rate of nearly 80% for their ecotype. Link.
According to the study, “Reproductive Ecology of Ocimum americanum L. and O. basilicum L. (Lamiaceae) in India”, their ecotype of Ocimum basilicum is mainly self-pollinating. Link.
According to the study, “Reproductive biology and Enzyme in Ocimum spp.”, their ecotype of Ocimum basilicum is mainly self-sterile – with a ratio of 75 %. Link.
According to the 2022 study from Nigeria, “Polyploidization and speciation: patterns of natural hybridization and gene flow in basil (Ocimum spp.)”, two ecotypes of Ocimum basilicum – B1 with 2n = 52 and B2 with 2n = 72 – crossed with an ecotype of Ocimum americanum pilosum (C1) and produced fertile seeds. Link.
It remains to be verified that this is not Ocimum americanum pilosum, as per 2n = 72, as the same Nigerian authors of these several studies have made some taxonomic or photographic errors.
Genetic Analyses
2n =16. 2n = 52. Link. 2 n48. 2n = 60. Link. etc. In fact, chromosome evaluations vary widely for Ocimum basilicum. Link.
According to the 2016 study, from Poland, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content of many accessions of Ocimum basilicum varies between 4,303 Mbp and 4,773 Mbp (between 4.4 and 4.9 pg/2C). Link.
According to the 2011 study, from Israël, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, the nuclear DNA content of the Ocimum basilicum ecotypes she analyzed varies from 2,853 to 3,394 Mbp (2.92 to 3.47 pg/2C). Link.
According to the 2010 study by Klaudija Carović-Stanko et al. from the University of Zagreb, “Genetic relations among basil taxa (Ocimum L.) based on molecular markers, nuclear DNA content, and chromosome number”, the nuclear DNA content of the Ocimum basilicum ecotypes she analyzed varies from 3.98 to 4.54 pg/2C). Link.
The complete chloroplast genome, of a green ecotype of Ocimum basilicum, was published in 2023. The chloroplast genome was 152,407 bp in length and contained a large single copy region (LSC) of 83,409 bp and a small single copy region (SSC) of 17,604 bp separated by a pair of inverted repeats (IR) of 25,697 bp. The genome contained 134 genes, including 89 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Link.
A recent study, conducted in January 2025, determined the genetic difference between Thai-type and Genovese Italian-type basil plants. “Chromosome-level assembly of basil genome unveils the genetic variation driving Genovese and Thai aroma types”. Lien.
The complete chloroplast genome, of a purple ecotype of Ocimum basilicum, was published in 2024. The assembled chloroplast genome consisted of 152,407 base pairs (bp), including a large single copy region (LSC) representing 83,409 bp and a small single copy region (SSC) covering 17,604 bp separated by a pair of inverted repeats (IR) of 25,697 bp. The chloroplast genome contained 132 genes, including 88 protein-coding genes, 36 transfer RNAs (tRNAs), and 8 rRNA genes. Link
In conclusion, Ocimum basilicum is a mainly self-pollinating species, depending on ecotypes and varieties, with a very strong propensity for intraspecific crossbreeding, a very strong propensity for sterile crossbreeding with Ocimum kilimandscharicum, and a low propensity, to be verified, for fertile crossbreeding with Ocimum americanum pilosum.
Ocimum kilimandscharicum
Caveat. I have already dealt with reproductive biology and interspecific crosses in Ocimum kilimandscharicum in another very long essay – and in an exhaustive manner: “Basils 2025” – Third Report: Reproductive biology and interspecific crossings in Ocimum kilimandscharicum”. I will therefore only present a summary in this article and invite readers to refer to this third report to consult it in its entirety. Lien.
I use both the species name, Ocimum kilimandscharicum, and its name in India, “Kapura”.
Description
The flower stems grow up to 30 cm long.
The flowers are white in color, sometimes with purple hues. The corolla is approximately 8 mm long and is slightly to moderately pubescent with long hairs. The flower stalk is very pubescent and approximately 2.5 to 3.5 mm long.
The calyx is approximately 3 to 4.5 mm long when mature and is green to green/purple in color depending on the ecotype. It is pubescent on its outer surface except for the escutcheon. The pistil is white or purplish in color depending on the ecotype.
The stamens are very long, with a white filament, and extend well beyond the corolla. Their anthers are orange in color.
The pollen grains are orange/brick red in color and hexacolpate in type.
The weight of 1,000 seeds is approximately 0.7 grams. The seeds are black in color, oval to oblong in shape, and approximately 1.5 mm long and 0.8 mm wide. According to Campion-Bourget et al. Link, they are smooth or have a finely granular ornamentation with irregular granulations. The hilum area is generally well marked. The abaxial surface has a rounded ridge.
There does not appear to be any dormancy in Ocimum kilimandscharicum seeds. When moistened, they produce a small amount of clear mucilage.
Reproductive Biology
During the summer of 2025, in our garden, I discovered that the first flower stems harvested from the only Ocimum kilimandsharicum plant that had germinated, accession PI 652052, from GRIN/USDA (incorrectly presented by their taxonomists as Ocimum americanum) bore almost no seeds—even though this plant was growing under a controlled pollination tent… and therefore free of insects.
Ocimum kilimandscharicum is therefore mainly self-sterile and thus subject to a quasi-obligatory allogamous regime.
Today, it remains to be determined whether the self-sterility of Ocimum kilimandscharicum occurs at the plant level (as with cabbages or sunflowers) or at the individual flower level (as with carrots) due to its protogynous nature.
The only way to find out is to cultivate a Kapura under a tent, covered with a mosquito net, accompanied by a small hive of pollinating insects inside. If the self-sterility of Ocimum kilimandscharicum is at the plant level, there will not be, really, any more seed production, despite inter-floral pollination, than in a situation without insects.
Last month, I incorrectly mentioned that there were no studies on the reproductive mechanisms of Ocimum kilimandsharicum. To validate my discovery regarding its almost self-sterility, I therefore set off again in search of information on the web… and I indeed found some in four studies:
It should be specified, above all, that the species Ocimum kilimandscharicum is very uncommon in gardens and very little investigated by researchers… because research is expensive. For example, a search on the US Pubmed website shows 1500 references for Ocimum basilicum, 847 for Ocimum tenuiflorum, and 47 for Ocimum kilimandscharicum! That is why we had to wait until 2018 for these three studies, on the reproductive processes characterizing Ocimum kilimandscharicum, to be published.
1. A Nigerian study, from 2018, highlighted that the seed production in Ocimum kilimandscharicum is higher when the diversity of pollinating insects is abundant. At 50 meters from the forest, the diversity of insect species is three times greater than at 220 meters – and the number of insects is double. Link
2. A study from Bangalore, in 2020, highlighted, in Ocimum kilimandscharicum, the lower amount of seeds in cage pollinations compared to open pollination gardens or pollination sites by the local bee Apis cerana. Link
3. A Kenyan study, from 2023, highlighted that plants of Ocimum kilimandscharicum growing under veiled pollination cages – hence, in strict autogamy – produced 103 seeds while those growing in gardens, under open pollination, produced 22,960. Link
Namely, about 230 times more in open pollination than in covered cages. This indicates that there is indeed a regime of nearly obligatory allogamy in Ocimum kilimandscharicum – whose self-sterility, according to this study, is 99.56%.
4. A Nigerian study, from 2022, “Polyploidization and speciation: patterns of natural hybridization and gene flow in basil (Ocimum spp.)”, highlighted that an ecotype of Ocimum kilimandsharicum crossed with an ecotype of Ocimum basilicum characterized by 2n = 72 – a chromosome number that also characterizes Ocimum americanum var. pilosum. However, all plants were highly sterile. Link.
Then, just after posting – and translating into English – my second report “Basil 2025”, I informed Peter Nick, the director of the Botanical Institute of Karlsruhe, of my discovery, who asked me if I thought there was a delay between the maturity of the stamens and that of the style in Ocimum kilimandscharicum.
It was then that I remembered my sequence of photos, taken in 2022, of the opening of an Ocimum kilimandscharicum flower. It is clearly visible there that the flower blooms with stamens completely devoid of pollen, while, as soon as it opens, an insect rushes to the bottom of the corolla to extract nectar – thus signaling the maturity of the female reproductive organ.
This is a process known as “proterogyny“ by which female cells mature before male cells to prevent self-fertilization.
I did not stop at this sequence of photographs and I went on to dissect a few floral buds ready to bloom in order to check that they were characterized by the same protogynous reproductive regime. And I took a few photographs of them.
It is clear that this self-sterility is not total. Yesterday, I had the opportunity to photograph the beginning of the opening of a Kapura flower whose stamens were covered with orange pollen. In this sequence, a butterfly rushes into the flower 12 seconds later – while the stamens are not yet fully open – and remains there foraging for 52 seconds.
As a preliminary conclusion, this almost total self-sterility, in Ocimum kilimandsharicum, explains all the better, of course, this species’ tendency to allow itself to be courted by the numerous pollinating insects buzzing from one Ocimum species to another.
As for the inter-species crossbreeding capabilities of Ocimum kilimandsharicum, I discussed them at length in my third report from the summer of 2022, mentioned above and entitled “Reproductive biology and interspecific crossings in Ocimum kilimandscharicum”. Link.
Here are some photographs of the interspecific crosses I obtained during a second wave of sowing. Some are already proving very exciting, with huge green or purple leaves. It remains to be seen how resistant they are to the cold winter temperatures.
Purple leaves 13 cm long with a 2.5 cm petiole
Genetic Analyses
According to genetic sequencing, 2n = 76 for Ocimum kilimandscharicum.
According to the 2016 study, from Poland, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content of an accession of Ocimum kilimandscharicum – PI 652052, from GRIN/USDA, incorrectly identified as Ocimum citriodorum – is 6738 Mbp (approximately 6.9 pg/2C). Link.
According to the 2010 study, from Israël, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, the DNA content of two accessions of Ocimum kilimandscharicum including PI 652052 from GRIN/USDA, incorrectly identified as Ocimum americanum pilosum – ranges from 4,572 to 4,637 Mbp (4.68 to 4.74 pg/2C). Link.
The complete chloroplast genome of an Indian Camphor ecotype of Ocimum kilimandscharicum was published in 2023. The chloroplast genome (cp) size is 151,741 bp, with a large single-copy region (LSC) of 82,882 bp and a small single-copy region (SSC) of 17,587 bp, separated by a pair of inverted repeat regions (IR) of 25,636 bp. The genome contains 135 predicted genes, including 90 protein-coding genes, 37 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Link.
In conclusion, Ocimum kilimandscharicum is a mainly self-sterile and cross-pollinating species – due to its protogyny – with a very strong propensity for inter-specific cross-pollination.
It is also very easy for gardeners to obtain hybrid plants of Ocimum kilimandscharicum. All they need to do is grow a few plants completely isolated from each other in their garden, surrounded by numerous other basil plants of Ocimum basilicum or Ocimum americanum. Due to their self-sterility, Ocimum kilimandscharicum plants are then, statistically, much more likely to be pollinated by male pollen from surrounding Ocimum basilicum or Ocimum americanum plants.
Ocimum tenuiflorum
Description
The flower stalks of Ocimum tenuiflorum are approximately 5 to 15 cm long and characterized by dense pubescence.
The interval between the (pseudo) whorls (composed of 6 flowers) is approximately 6 mm.
The flowers are of various colors, combining purple or green calyxes with pink-purple corollas.
It should be noted that there is a variety in India—originally from Almora in Uttarakhand—renowned for its completely white corollas with green calyxes. Link.
The flower stalks are very long, measuring 2.5 mm to 3 mm, and are pubescent.
The calyxes are purple to green/purple in color and 3 to 5 mm long. Their pubescence varies depending on the ecotype and can be dense. The shield of the upper lobe is 2.5 to 3 mm long.
The corollas are approximately 3.5 to 5.5 mm long.
The style is 5 to 6 mm long. The stamens extend 2 mm beyond the corolla.
The pollen grains are round, yellow in color, and hexacolpate. They are approximately 35 to 50 microns in diameter, depending on the ecotype.
The seeds are various colors (red/brown/black) and globular to subglobular in shape, with a shiny, finely granular coat that becomes mucilaginous when moistened. The weight of 1,000 seeds is 0.2 to 0.3 grams. Depending on the ecotype, they are 934 to 1,317 microns long and 962 to 697 microns wide. Their dormancy at harvest is 100% and requires about 4 months to be lifted.
Reproductive Biology
During the summer of 2025, I cultivated two green-leaved ecotypes of Ocimum tenuiflorum – PI 652057 from Cuba and PI 288779 from Gujarat – under controlled pollination conditions (i.e., strictly self-pollinated and without pollinating insects). It turned out that the plants produced only a few seeds, the fertility of which I have not yet tested.
I therefore concluded that Ocimum tenuiflorum was undoubtedly subject to a certain degree of self-sterility – either at the flower level or at the plant level.
It is possible that the low seed count can be explained by delayed pollen maturity on the first day of anthesis, due to the positioning of the controlled pollination tents in the shade of two olive trees.
The following studies, which I have just discovered, confirm the partial self-sterility and cross-pollination regime of Ocimum tenuiflorum due to its protandry.
According to the 1997 study, “Reproductive Biology and Enzyme studies in Ocimum spp”, seed production in open pollination, with insects, was 90%, whereas it was only 28% in controlled pollination tents without insects. Link.
It means that seed production is three times greater under a regime of open pollination with insects.
According to the 2010 study, “Floral biology of Tulsi (Ocimum sanctum)”: «In the two-day age of flower, its anther dehisced on first day and stigma was not receptive. The latter became receptive on second day but by that time pollen has become non-viable. Therefore, flowers of tulsi were protandrous and cross-pollinated, however, but self-incompatibility was absent. » Link.
Conversely, a 1997 study indicated that pollen dehiscence could be observed before the start of anthesis on very sunny days. According to this study, plants undergoing open pollination outdoors produced three times more seeds than those under controlled pollination tents without insects. Link.
According to the 2007 study, “Floral biology, mellitophily and pollination ecology of Tulsi (Ocimum sanctum)”. « Differences in different pollination treatments (i.e. insect, open, wind and self-pollination) on different yield parameters (e.g. number of seed set per inflorescence, yield per plant and per plot, test weight of seeds and percent germination) were significant. Seed setting was found to be highest in insect pollination treatment (1045.66 seeds/inflorescence) followed by 565 seeds/inflorescence in open pollination. However, seed set was found to be very low in other two treatments i.e. wind pollination and self-pollination.
Similar results were observed in case of yield per plant and yield per plot. Test weight and percent germination was found to be similar for the three pollination treatments i.e. for insect pollination, open pollination and wind pollination respectively but in case of selfpollination it was near about half of the former three due to deformed and under sized seeds in the latter treatment. Pollination experiments clearly revealed that tulsi flowers are highly benefited from insect visits .Its yield parameters showed that it is a cross-pollinated and entomophilous plant .In general, the yield in this plant is pollinator limited i.e. there is scarcity of pollinators to achieve the maximum goal as is evident by yield data in insect pollination treatment. The structure shape and fertility status of the flower clearly revealed that it has bee pollinated flowers and melittophily pollination syndrome existed in tulsi.» Link.
Genetic Analyses
Ocimum tenuiflorum is a diploid species with various chromosome formulas depending on genetic analyses. 2n = 32. Link. 2n = 36. Link.
According to the 2016 study, from Poland, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content of two GRIN/USDA accessions of Ocimum tenuiflorum – PI 652057 from Cuba and PI 288779 from Gujarat – is 900 Mbp and 1848 Mbp (and 0.92 and 1.89 pg/2C), respectively. Link.
Klaudija Carović-Stanko et al., from the University of Zagreb, in their 2010 study entitled “Genetic relations among basil taxa (Ocimum L.) based on molecular markers, nuclear DNA content, and chromosome number”, analyzed an ecotype of Ocimum tenuiflorum from Germany (MAP01628) and estimated its genome size to be 386 Mbp. Link
Unlike his subsequent study, which mistakenly used four temperate Tulsi ecotypes, it would appear that this time it is an authentic ecotype of Ocimum tenuiflorum, as the results obtained by Klaudija Carović-Stanko correspond to those of other studies.
The complete chloroplast genome of a purple Krishna ecotype of Ocimum tenuiflorum was published in 2021. The cp genome is 151,758 bp long, comprising a large single copy region (LSC) of 82,794 bp, a small single copy region (SSC) of 17,592 bp, and a pair of inverted repeat regions (IR) of 25,686 bp. The cp genome of Krishna Tulsi encodes 129 genes, including 90 protein-coding genes, 31 transfer RNA (tRNA) genes, and 8 ribosomal RNA (rRNA) genes. Link.
The complete chloroplast genome of a green Rama ecotype of Ocimum tenuiflorum was published in 2021. The total length of the circular chloroplast genome was 151,722 bp. It includes an inverted repeat (IR) region with a length of 25,677 bp, a large single copy (LSC) region of 82,781 bp, and a small single copy (SSC) region of 17,587 bp. The chloroplast genome contains 134 genes, including 88 protein-coding genes, 38 transfer RNA genes, and 8 ribosomal RNA genes. Link.
In conclusion, Ocimum tenuiflorum is primarily an outcrossing species – due to its protandric nature – with a propensity for intraspecific crossbreeding.
Ocimum americanum pilosum
Description
The flower stems are, on average, 20 to 30 cm long in “Sweet Dani” and 17 to 30 cm long in “Esfahan. PI 253157” – namely, two ecotypes of Ocimum americanum var. pilosum.
I would like to point out that this year, the tallest Basil floral stems I measured in the garden were 36 cm long in “Esfahan.” This record was broken on the balcony by a cross between Ocimum kilimandscharicum and Kapura X. SP. 01/2025, which grew to a length of 38 cm.
The interval between the verticils (composed of 6 flowers) is relatively wide. In Lemon Basil cultivars, the interval between verticils depends on the variety and ecotype: it varies from 16 mm to 19 mm.
It should be noted that this interval, averaging 17.5 mm, is virtually identical for the ecotypes “Kali”, “Mrs. Burns”, “Sweet Dani” et Lime Thai” – regardless of the size of the plant.
The bracts are oval in shape and 5 to 9 mm long.
The calyxes are 5.5 to 6.5 mm long with a dry shield that can reach 5.5 mm in width. The inner surface of their lower lip is hairless.
The corollas are 7 to 11 mm long. They are white in color, even in ecotypes with anthocyanins.
Pollen grains are spheroid in shape with a rough exine. They are hexacolpate (87%) and octacolpate. Link According to the study, “The size of viable pollen is correlated with ploidy level, as evidenced by a polyploid series of Ocimum L. from Thailand”, pollen grains are approximately 58 to 81 microns in diameter. Link.
The weight of 1,000 seeds is 1.4 g to 2.1 g. The seeds are oblong to elliptical in shape and black in color. According to Campion-Bourget et al. Lien, they are approximately 2.3 to 2.6 mm long and 1.5 mm wide. When moistened, they produce a mucilage.
Reproductive Biology
Unfortunately, there are currently only a few published studies on the reproductive biology of the species Ocimum americanum.
The study, “Reproductive Ecology of Ocimum americanum L. and O. basilicum L. (Lamiaceae) in India,” mentions the high self-fertility of an ecotype of Ocimum americanum – up to 88% – without specifying whether it is an ecotype of Ocimum americanum var. pilosum… but this seems more than likely given its characteristic reproductive biology. This study mentions that the species has three reproductive systems: autogamy, geitonogamy, and xenogamy. Link.
According to the 2016 study, from Nigeria, “Comparative reproduction mechanisms of three species of Ocimum L. (Lamiaceae)”. Depending on the ecotype, pollen dehiscence occurred either before or after anthesis in the three ecotypes of Ocimum americanum. One of these ecotypes, named “Ocimum americanum,” in a controlled pollination tent, was only 13% self-fertile, while the other two, named “Ocimum canum,” were 82/86% self-fertile. The latter are likely to be an ecotype of Ocimum americanum var. pilosum (with 8 mm stamens) and an ecotype of Ocimum americanum var. americanum (with 4 mm stamens). Link.
In this study, the three ecotypes named Ocimum americanum and Ocimum canum were, supposedly, tetraploids with 2n = 52, as was an ecotype of Ocimum basilicum (B1).
According to the 2018 study, from Nigeria, “Pollination Mechanisms in two variants of Ocimum canum”, both ecotypes of Ocimum canum are 80-85% self-fertile. Once again, these are an ecotype of Ocimum americanum var. pilosum (C1) and an ecotype of Ocimum americanum var. americanum (C2) based on the size of their floral organs and the space between the whorls. Link.
If this is the case for these last two studies, it means that there are relatively self-fertile ecotypes of Ocimum americanum var. americanum.
According to the 2022 study, from Nigeria, “Polyploidization and speciation: patterns of natural hybridization and gene flow in basil (Ocimum spp.)”, an ecotype of Ocimum basilicum (B1) crossed with an ecotype of Ocimum americanum var. pilosum (C1) and produced fertile seeds. Link.
In the summer of 2025, I was able to verify for myself that two plants of the Iranian ecotype “Esfahan” produced a normal amount of seeds while growing in an insect-proof pollination tent under strictly self-pollination conditions.
The question arises, once again, as to the degree of potential interspecific allogamy of Ocimum americanum pilosum.
This year, I did not observe any obvious hybridization in plants grown from seeds of the “Esfahan” ecotype cultivated through open pollination in 2022 – among 30 types of Basil. However, I did not have enough plants to draw any relevant conclusions.
Today, when I observe the morphological diversity of my 50 or so hybrid plants resulting from spontaneous crosses involving Ocimum kilimandscharicum and Ocimum bisabolenum – as mother plants – it is certain that they come from seeds derived, for the most part, from Ocimum basilicum pollen. Nevertheless, for some plants, given the shape of their leaves, the size of their white flowers, and the extreme length of their flowering stems, it would appear that the pollen also comes from Ocimum americanum var. pilosum – at least in the case of hybrid plants of Ocimum kilimandscharicum.
As for the capacity for interspecific crossbreeding of Ocimum americanum var. pilosum, this remains to be validated, more specifically with regard to Ocimum kilimandsharicum, but also with regard to Ocimum bisabolenum. This is what I intend to do during the summer of 2026, using cross-pollination tents, each of which will contain a small hive of pollinating bumblebees.
Namely, in order to verify, in this type of two-way hybridization, the quantity of fertile seeds produced and the number of proven interspecific crosses.
In any case, it seems to have been validated by an amateur breeder, in the USA, who claims to have cultivated hybrids of Ocimum americanum var. pilosum, resulting in the creation of a variety called “Linnamon” – a cross between Lemon Basil (containing Citral) and Cinnamon Basil (containing methyl cinnamate). See the blog “Basically about Basil”. Link.
It should be noted that even if spontaneous inter-species hybridization does occur, albeit extremely rarely – except in the case of common hybrids involving Ocimum kilimandsharicum – these remain within the same “group” of Basil species identified by Alan Paton, a geneticist at Kew, at the beginning of the century.
This is the “Basilicum Group,” which includes Ocimum basilicum, Ocimum kilimandscharicum, Ocimum americanum var. americanum, and Ocimum americanum var. pilosum. In 2022, I added the species Ocimum bisabolenum to this group. I did so behind Alan Paton’s back, as he had refused to consider the issue of temperate Tulsi, since 2017, and had responded to me with a half-hearted answer, cowardly sidestepping the issue by referring to Ocimum americanum var. pilosum.
Genetic Analyses
Ocimum americanum var. pilosum is a species with various chromosome formulas depending on genetic analyses. 2n = 72. 2n = 78. Link. Link.
According to the 2016 study, from Poland, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content of various accessions of Ocimum americanum var. pilosum varies between 7,169 and 7,364 Mbp (7.3 to 7.6 pg/2C).. Link.
According to the 2010 study, from Israël, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, the nuclear DNA content of two accessions of Ocimum americanum var. pilosum – PI 652060 and “Sweet Dani” – ranges from 4,808 to 5,515 Mbp (4.92 to 5.64 pg/2C). Link.
According to the 2010 study by Klaudija Carović-Stanko et al. from the University of Zagreb, “Genetic relations among basil taxa (Ocimum L.) based on molecular markers, nuclear DNA content, and chromosome number”, the nuclear DNA content of the Ocimum americanum var. pilosum ecotypes, she analyzed, varies from 6.45 to 7.43 pg/2C). Link.
It should be noted that his study, like other genetic studies, correctly places two ecotypes purportedly of Ocimum basilicum var. purpurascens – with 2n = 72 and nuclear DNA of 6.45 to 7.43 pg/2C) – in the clade of Ocimum americanum var. pilosum.
The complete chloroplast genome of a Lemon Basil, Ocimum americanum var. pilosum, was published in 2023. The chloroplast genome of Ocimum americanum var. pilosum was 152,460 bp in length, containing a large single copy region (LSC) of 83,459 bp and a small single copy region (SSC) of 17,607 bp, separated by a pair of inverted repeats (IR) of 25,697 bp. The genome contained 134 unique genes, including 89 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Link.
In conclusion, Ocimum americanum var. pilosum is a primarily self-pollinating species with a certain tendency toward intraspecific cross-pollination, as well as a much lesser tendency toward interspecific cross-pollination.
Ocimum americanum americanum
Description
The interval between the verticils (composed of 6 flowers) is very small. Thus, there are up to 35 of them on a 21 cm flower stalk in Zambian camphor basil – with an average interval of 6 mm.
Pollen grains are spheroidal in shape with a rough exine. A 2010 study, “Pollen grain morphology of three species and a variety of Ocimum Linn. (Lamiaceae) in Southwestern Nigeria,” analyzed an ecotype whose pollen grains are acolpate, monocolpate, bicolpate, pentacolpate, hexanocolpate, heptacolpate, and octacolpate. Link.
According to the study, “Pollen grains and seed morphology as related to biochemical patterns in five species of genus Ocimum of Saudi Arabia”, pollen grains are approximately 25 to 27 microns in diameter. Link. This is most likely an ecotype of Ocimum americanum var. americanum, as the seeds are approximately 1.5 mm long. According to the study, “The size of viable pollen is correlated with ploidy level, as evidenced by a polyploid series of Ocimum L. from Thailand”, pollen grains are approximately 44 to 64 microns in diameter. Link.
The 1,000 seeds weigh between 0.35 g and 0.75 g. They are ovoid in shape and black in color. According to Campion-Bourget et al. Link, they are approximately 1.3 to 1.5 mm long and 0.8 to 0.9 mm wide. The abaxial surface of the seed has a distinct ridge. When moistened, they produce a thin, transparent mucilage.
Their dormancy at harvest is 100% and requires approximately 80 days to be completely lifted. It gradually lifts after 3 weeks.
Ocimum canum. 5, whole nutlet, adaxial face (x 90) ; 61 et 62, enlarged portion showing wax deposits on pericarp surface (x 5000 and x 10000). Ocimum americanum L.: 7, whole nutlet, abaxial face (x 70) ; 8, reticulate-foveate pattern of pericarp (x 300). Campion-Bourget et al. Link
Reproductive Biology
According to the 2008 study, from Brazil, “Floral biology and reproductive mechanisms of the Ocimum canum Sims (Lamiaceae)”, The ecotype analyzed exhibits a reproductive regime with a predominance of cross-pollination. «In the pre-anthesis stage, although the flower remains closed, pollen grains are released onto the stigma, which is already receptive. At the beginning of anthesis, a low pollen grain germination rate of 1.70% was observed. The flower’s longevity is approximately 24 hours. With regard to the reproductive system, Basil has a higher rate of natural cross-pollination than natural self-pollination (Table 3), indicating that the species is preferentially allogamous.» Link.
According to this study, five times more seeds were produced through open pollination (cross-pollination) than through pollination under a covered cage (self-pollination). In addition, only 30% of seeds produced through self-pollination germinated, compared to 69% of seeds produced through open pollination with insects.
This means that, for this ecotype of Ocimum americanum var. americanum, free pollination by insects produces more than 10 times more fertile seeds than strict self-pollination without insects.
According to the 2016 study, from Nigeria, “Comparative reproduction mechanisms of three species of Ocimum L. (Lamiaceae)”. Depending on the ecotype, pollen dehiscence occurred either before or after anthesis in the three ecotypes of Ocimum americanum. One of these ecotypes, named “Ocimum americanum,” in a controlled pollination tent, was only 13% self-fertile, while the other two, named “Ocimum canum,” were 82/86% self-fertile. The latter are likely to be an ecotype of Ocimum americanum var. pilosum (C1 with 8 mm stamens) and an ecotype of Ocimum americanum var. americanum (C2 with 4 mm stamens). Link.
It should be noted that the pollen of Ocimum americanum and Ocimum canum C2 was dehiscent after the start of anthesis, whereas that of Ocimum canum C1 – namely, Ocimum americanum var. pilosum – was dehiscent before anthesis.
According to the 2018 study, from Nigeria, “Pollination Mechanisms in two variants of Ocimum canum”, Both ecotypes of Ocimum canum are 80-85% self-fertile. Once again, these are an ecotype of Ocimum americanum var. pilosum (C1) and an ecotype of Ocimum americanum var. americanum (C2), based on the size of their floral organs. Link.
If there are no other errors, apart from those of specific differentiation, for these last two studies, this means that there would be relatively self-fertile ecotypes of Ocimum americanum var. americanum.
This remains to be verified. In any case, during the summer of 2025, plants of various Camphor ecotypes from Zambia did not appear to produce a normal amount of seeds while growing in an insect-proof pollination tent under strictly self-pollination conditions. Assessing the self-sterility, of various ecotypes of Ocimum americanum var. americanum, will be one of my goals for 2026.
According to the 2022 study, from Nigeria, “Polyploidization and speciation: patterns of natural hybridization and gene flow in basil (Ocimum spp.)”, the ecotypes of Ocimum basilicum produced only weak or sterile hybrids when crossed with ecotypes of Ocimum americanum var. americanum. Link.
Genetic Analyses
Ocimum americanum var. americanum is a species with various chromosome formulas depending on genetic analyses. 2n = 24. Link. 2n = 26. Link. 2n = 52. Link. Link.
According to the 2016 study, from Poland,-, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content, of various accessions of Ocimum americanum var. americanum, varies. It is approximately 2300 Mbp (2.35 pg/2C) for accessions PI 254352 (Iraq), PI 253158 (Iran), PI 652062 (Tanzania), and PI 652058 (Togo), and from 4342 to 4460 Mbp (4.5 pg/2C) for accessions PI 500945 (Zambia), PI 500944 (Zambia), and PI 500942 (Zambia). Link.
According to the 2010 study, from Israël, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, the nuclear DNA content of various accessions of Ocimum americanum var. americanum – PI 254352, PI 500945, PI 652062, PI 500953 – ranges from 1,762 to 3,607 Mbp (1.08 to 3.69 pg/2C). Link.
The complete chloroplast genome of an ecotype of Ocimum americanum americanum was published in 2024 under the name Ocimum africanum. The chloroplast genome of Ocimum americanum var. americanum was 152,365 bp long and contained a large single copy region (LSC) of 83,367 bp and a small single copy region (SSC) of 17,604 bp, separated by a pair of inverted repeats (IR) of 25,697 bp. The genome contained 131 unique genes, including 50 protein-coding genes, 37 tRNA genes, and 8 rRNA genes. Link.
In conclusion, Ocimum americanum var. americanum is a predominantly outcrossing species with a tendency toward intraspecific crosses.
Ocimum campechianum
Description
The inflorescences are composed of verticils of six flowers, spaced 0.8 cm to 2 cm apart, grouped in bracteate pseudo-racemes, reaching 8 cm long at anthesis and 15 cm long at maturity.
The floral peduncles are bristly, 1 to 1.5 mm long in flower, becoming reflexed in fruit, 4 to 7 mm long.
The bracts are oval or sub-rhomboid, persistent, with an acute apex.
The calyx is 2.5 to 3 mm long at anthesis, reaching 8 mm in length at maturity, with bristly edges.
The corolla is white, lilac, or purple, 3 to 4 mm long.
The stamens are glabrous and 5 to 6 mm long, with a white or purplish filament, while the style is 5 mm long. The pollen is white and the anthers are white or purplish.
The seeds are obovoid to elliptical, 1.5 to 2 mm long and brown-black in color. When moistened, they produce abundant mucilage. There is a certain level of dormancy in Ocimum campechianum. Link.
This description is taken from the 2017 study, “Taxonomic revision of Ocimum (Lamiaceae) in Argentina” by Nataly O’Leary. Link.
F. Seed. E. Calyx. D. Inflorescence.
Reproductive Biology
According to the 2007 study, “Biologia reprodutiva e citogenetica da alfavaca do campo, Ocimum campechianum”, the self-incompatibility ratio, i.e., self-sterility, of Ocimum campechianum is approximately 64%. Link.
It seemed to me, in fact, during the summer of 2025, that the only plant I placed under a controlled insect-proof pollination tent, bore very few seeds.
Its flowers are protandrous – meaning that the pollen matures before the stigma does.
Genetic Analyses
According to the 2016 study from Poland, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content of an accession of Ocimum campechianum is 1,154 Mbp (approximately 1.2 pg/2C). Lien .
According to the 2010 study, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, The DNA content of an accession of Ocimum campechianum is 928 Mbp (approximately 0.95 pg/2C). Lien.
Ocimum campechianum. 2n = 48. Link.
In conclusion, Ocimum campechianum is a highly self-sterile and cross-pollinating species, with a strong propensity for intraspecific crossbreeding.
Ocimum carnosum/selloi
Description
The inflorescences are composed of whorls of six flowers, spaced 1 to 2 cm apart, grouped in bracteate pseudo-racemes, reaching 3 cm in length at anthesis and 15 to 25 cm in length at maturity.
The bracts are oval, sparsely pubescent, and deciduous at the beginning of anthesis. They are 6 to 7 mm long. They develop into a cup-shaped auxiliary nectary.
The flower peduncles are very hairy, 1.5 to 3 mm long at anthesis and fruiting stage, somewhat reflexed at fruiting stage.
The calyxes are 2.5 to 3 mm long at anthesis, up to 10 mm long at maturity. They are subglabrous to bristly.
The corollas are pale blue or dark purple and 4 to 8 mm long.
The stamens are pink to purplish in color; they are 5 mm long; the upper pair is hairy at the base, while the lower pair is hairless. The anthers are yellow or purple in color. The purplish style is 7 mm long.
The pollen is white in color.
The seeds are obovoid in shape and 1.5 to 2 mm long. They are light brown to dark brown in color and are slightly striated to reticulated. When moistened, they do not produce mucilage. There is a certain level of dormancy in Ocimum carnosum/selloi.
This description is taken from the 2017 study, “Taxonomic revision of Ocimum (Lamiaceae) in Argentina” by Nataly O’Leary. Link and from the study “El genero Ocimum en el nordeste del Brasil”. Link.
Reproductive Biology
According to the 2008 study, “Reproductive biology of Ocimum selloi populations”. «This species is self-compatible, forming fruits and seeds under both free pollination and spontaneous self-pollination, which indicates it has a great reproductive versatility, assuring genetic variability. Seed germination was also high in all four populations». Link.
According to the 2015 study, “Genetic and chemical diversity of native populations of Ocimum selloi”: «Ocimum selloi populations present mixed reproductive systems, presenting auto-fertilization, and out-crossing». Link
In fact, there is a huge genetic and chemotypic difference between the Ocimum selloi populations found in Central America and those found in South America.
According to my own observations in November 2025, the only Ocimum selloi plant – whose geographical origin I do not know – which I isolated under an insect-proof controlled pollination tent, in strict self-pollination, produced very few seeds. I counted them on four branches, taking only the first six verticils, and there were only 26. In contrast, the first six verticils of four branches, taken from two plants grown under open pollination, produced just over 200 seeds. That is eight times more with open pollination compared to strict self-pollination – meaning a self-sterility of nearly 90%.
Genetic Analyses
According to the 2016 study, from Poland, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content of an accession of Ocimum selloi/carnosum is 2,983 Mbp (approximately 3.5 pg/2C). Link.
According to the 2016 study, from Israël, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, the DNA content of an Ocimum selloi accession is 2,172 Mbp (approximately 2.22 pg/2C). Link.
In conclusion, Ocimum selloi is a mainly self-sterile, cross-pollinating species with a strong propensity for intraspecific hybridization.
Ocimum gratissimum
Description
The inflorescences are composed of verticils of six flowers, spaced 0.7 mm apart, grouped in bracteate pseudo-racemes, reaching 15 to 17 cm in length at maturity.
The sessile, ovoid bracts are 3 to 12 mm long.
The calyxes are 3 to 5.5 mm long at anthesis and 6 to 8 mm long at fruiting.
The corollas are 2 to 5 mm long. They are green or greenish-white in color. Their inner surface is hairless and their outer surface is more or less pubescent depending on the ecotype.
The flower stalk is 2 to 4 mm long.
The filaments and stigmas of the pistils are various colors depending on the ecotype.
The stamens extend beyond the corolla by about 2 mm. The upper stamens are pubescent at their base. Their filaments are white. The anthers are yellow or yellow/orange.
The pollen is yellow. Its grains are approximately 40 to 65 microns in size and are mainly hexacolpate.
The 1,000 seeds weigh between 0.8 g and 1.2 g. They are subglobose to globose in shape. According to Campion-Bourget et al. Link, they are largely faveolate and measure 1.19 to 1.36 mm in length and 1.25 to 1.4 mm in width.
Their dormancy at harvest is 100% and requires about one month to be completely lifted. They produce a very thin film of transparent mucilage when moistened – so light that this species has a reputation for producing seeds that do not produce mucilage.
Reproductive Biology
During the summer of 2025, I cultivated various ecotypes of Ocimum gratissimum under an insect)-proof controlled pollination tent (in strictly self-pollination). It turned out that the plants produced very few seeds, the fertility of which I have not yet tested.
According to the study, “Morfologia e biologia floral da alfavaca cravo (Ocimum gratissimum L.)”, there is, in fact, a certain degree of allogamy and auto-sterility, with Ocimum gratissimum. Link.
« The stigma receptivity test showed that 100% of the flowers analyzed were tested using the peroxidase test, of which 32.1% had pollen on the stigma during anthesis and post-anthesis and 67.9% had no pollen on the stigma. The stigma remained receptive during all three stages of floral development (100%), and pollen grains were present at a rate of 69.69% during pre-anthesis, 16.13% during anthesis, and 14.16% during post-anthesis, remaining available throughout the observation period. Analysis of the stigmas showed that pollen tube growth occurred only in post-anthesis.».
According to the study, “Phenological studies on Ocimum gratissimum ”, Ocimum gratissimum is characterized by a low level of protandry. Link.
According to the study, “Reproductive biology and Enzyme in Ocimum spp.”: «Anther dehiscence was observed during pre-anthesis on sunny, bright days. On cloudy days, dehiscence was delayed until post-anthesis». The authors mention 50% self-sterility for the ecotype of Ocimum gratissimum analyzed. Link.
Genetic Analyses
According to the 2016 study, from Poland, “Genetic characterization of Ocimum genus using flow cytometry and inter-simple sequence repeat markers”, the DNA content of three accessions of Ocimum gratissimum varies between 1,848 Mbp and 2,230 Mbp (approximately 1.83 to 2.28 pg/2C). Link.
According to the 2010 study, from Israël, “Estimation of nuclear DNA content of cultivated Ocimum species by using flow cytometry”, the DNA content of several accessions of Ocimum gratissimum varies from 1,308 to 1,839 Mbp (approximately 1.34 to 1.88 pg/2C). Link.
The complete chloroplast genome of an ecotype of Ocimum gratissimum was published in 2021. The chloroplast genome of Ocimum gratissimum is 152,469 bp long and contains a large single-copy region (LSC) of 83,614 bp and a small single-copy region (SSC) of 17,607 bp, separated by a pair of inverted repeats (IR) of 25,624 bp. The genome contains 138 unique genes, including 85 protein-coding genes, 45 tRNA genes, and 8 rRNA genes. Link.
In conclusion, Ocimum gratissimum is a highly outcrossing species.
