Allelopathy and Companion Planting.

The language of botany and medicine can be quite poetic. The words are derived from historical languages and may (usually) contain Latin or Greek terms (1) and each word if etymologically (2) broken down is a story in itself. As a somewhat appropriate example I present an example as given by Babbel Magazine (3). “The word avocado comes from Spanish aguacate (sometimes ahuacate), which in turn comes from the Nahuatl ahuacatl, meaning testicle.” Using the Linnaean binomial nomenclature terminology (4) we have the name Persea americana for the avocado. Genus name “Persea” comes from the Greek name persea for an Egyptian tree (Cordia myxa) and the specific epithet “americana” means of the Americas.

  1. or any other number of languages. Do not be surprised to come across Egyptian, Arabic or even languages that are no longer spoken.
  2. Etymology – the origin of a word and the historical development of its meaning.
  4. binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin grammatical forms, although they can be based on words from other languages. The first part of the name – the generic name – identifies the genus to which the species belongs, whereas the second part – the specific name or specific epithet – distinguishes the species within the genus.

Persea – sacred fruit-bearing tree of Egypt and Persia, c. 1600, from Latin persea, from Greek περσέα (perséa); the tree name in Greek, though referring to the tree in Egypt, reflects its Persian origin. Used from early 19th Century.

  1. By Rohalamin – Own work, CC BY-SA 4.0, httpscommons.wikimedia.orgwindex.phpcurid=105841145
  2. By Rohalamin – Own work, CC BY-SA 4.0, httpscommons.wikimedia.orgwindex.phpcurid=105841314
  3. By Marco Schmidt [1] – Own work, CC BY-SA 3.0, httpscommons.wikimedia.orgwindex.phpcurid=7892578

There is some controversy over the definition involving testicles. The fruit certainly resembles the aforementioned organs (freshly shorn ones perhaps) and their tendency to hang as they do (often in pairs) also reinforces the testicle imagery. The Nahuatl word for testicle is “ātetl”; derived from tetl (stone) and the translation of ĀTE-TL is literally “water-stone” (1). One definition involves the plant itself (a tree) : “ahuacatl comes from the Proto-Nahuan (predecessor language of Nahuatl) word pāwatl, referring to large tree species (2). This is the underpinning word for Nahuatl’s oak tree (āhuacuahuitl) and avocado tree (āhuacacuahuitl)” and another involves the type/shape/texture of the fruit much in the way the Nahuatl word tzapotl (sapote) can be used to describe all soft, sweet fruit.

  1. (another common word is xitetl)
  2. although Nawatl Scholar notes that “ahuacatl comes from a proto-Nahuan word *pawata which also means “avocado” – the word pawatl is still used for wild avocado in some Nahuatl varieties” and that “in Nahuatl speaking communities I have never met anyone who considered the word /a:wakatl/ to refer to anything but avocadoes”.

The testicle nomenclature in this case is likely a tongue in cheek reference to the fruit – much in the same way we might refer to the testicles as “nuts” (or a Mexican might euphemistically refer to testicles as huevos “eggs”). Some plants (1) don’t even allude to a plant being testicle like and just straight out call it a testicle plant. For instance.

  1. See Post Bifora. Another Cilantro Substitute?
Bifora testiculata.
An interesting culinary herb that deserves more attention.

This is just one small example of the stories that names can tell.

The word I’m looking at today is “allelopathic”. When I first started my studies over 30 years ago I had never come across this word. I was exposed to many medicinal terms specific to herbal medicine such as adaptogenic, depurative and balsam and many archaic terms such as antiphlogistic and gastrosis which are no longer in general use (1) but this word, allelopathic, only entered my consciousness less than a decade ago.

  1. See Post Glossary of Terms used in Herbal Medicine. for an exploration of some of these words/terms.

So what does allelopathy/allelopathic denote?

Its most basic definition refers to all the biochemical interactions among plants, or between plants and microorganisms; this can be further edified by the explanation that Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms (neighbouring plants). These biochemicals are known as allelochemicals and can have beneficial or detrimental effects on the target organisms and the community.

Allelopathy has been known for at least 2000 years. Willis (2000), reviewing aspects of the history of allelopathy notes that the Romans, recognized allelopathic phenomena. Circa 36BC, the author Varro, who wrote more than 600 books, observed the harmful effect that walnut tress could have on adjacent species. First observed in forest systems, especially through the dominance and succession of tree species, it was given a name and defined in 1937 by the Austrian professor Hans Molisch in his book Der Einfluss einer Pflanze auf die andere – Allelopathie (The Effect of Plants on Each Other – Allelopathy) where he used the term to describe biochemical interactions by means of which a plant inhibits the growth of neighbouring plants. In 1984, Elroy Leon Rice in his monograph on allelopathy enlarged the definition to include all direct positive or negative effects of a plant on another plant or on micro-organisms by the liberation of biochemicals into the natural environment.

The origin of the word comes from the Greek allelo (“of each other’’ or ‘’mutual”) and pathos (“suffering”). (1)

  1. allilon- (αλλήλων) and -pathy (πάθη) (meaning “mutual harm” or “suffering”),

This particular etymology of the word implies that these interactions are negative. Currently however the meaning of allelopathy also includes understanding that allelopathy includes positive interactions, such as cooperative phenomena or microorganism stimulation. These interactions are done by allelochemical compounds, released by the plant into its environment. Most often, these compounds are secondary metabolites and belong to a wide variety of biochemical families. They can be released by the roots (exudation), the aerial parts (leaching, volatilization) or residue decomposition of dead plants.

In 1996 the International Allelopathy Society (IAS) defined allelopathy as “Any process involving secondary metabolites produced by plants, algae, bacteria and fungi that influences the growth and development of agriculture and biological systems.

Allelopathy can be a problem in environments where non-native plants have been introduced. One plant (well tree actually) with a well known (although possibly contentious) allelopathy with environmental consequences is Leucaena leucocephala.

Leucaena leucocephala is native to southern Mexico and Central America and is now naturalized in more than 130 countries. This species is listed in the world’s 100 worst invasive alien species and is considered to be an aggressive colonizer. It forms dense stands which threaten native plant communities. Possible evidence for allelopathy of L. leucocephala has accumulated over the last few decades. The extracts, leachates, root exudates, litter, decomposing residues, and rhizosphere (1) soil of L. leucocephala increased the mortality and suppressed the germination and growth of several plant species, including weeds and woody plants. These observations suggest that L. leucocephala is allelopathic and contains certain allelochemicals. Those allelochemicals may release into the rhizosphere soil during decomposition process of the plant residues and root exudation.

  1. The rhizosphere is the zone of soil surrounding a plant root where the biology and chemistry of the soil are influenced by the root.
Guajes – Leucaena leucocephala – an edible and medicinal tree. See Post Guaje. for more information on this plant

Two quelites with allelopathic qualities I have previously Posted on are Aceitilla : Bidens pilosa and Quelite : Piojito : Galinsoga parviflora. Check them out.

One way of understanding allelopathy is through the practice of companion planting.

Companion planting is the careful placement of plants (especially vegetables and herbs) which have been shown to have beneficial effects on one another. It also takes into account plants that should not be planted together as they may have negative effects on each other. The practice of companion planting has ancient roots. Commonly thought of as a type of folk knowledge (much like “folk” medicine)(1) companion planting occupies the same sphere as aromatherapy in that it is a valuable and beneficial practice but is generally misunderstood and is practised poorly as a result.

  1. Folk medicine is a mixture of traditional healing practices and beliefs that might include herbal medicine, spirituality and manual/physical therapies or exercises (and possibly magical or pseudomagical ritual) in order to diagnose, treat or prevent an ailment or illness. The World Health Organization states that it is mostly practiced by indigenous or native populations and as much as 80% of the population in certain countries within Asia and Africa rely on it for primary care. These practices are generally denigrated by modern medical practices/practitioners.

The most relevant (for this Blog anyway) example of companion planting is that of the Three Sisters, corn, beans and squash. These three plants were typically planted together and each benefitted the growth of the others. The corn provided a frame upon which the beans could climb/grow, the beans fixed nitrogen in the soil aiding both the corn and the squash and the squashes rambling leafy growth habit provided a type of living mulch which assisted by retaining water in the soil, suppressing weed growth and protecting the soil in which the roots of all three grow. This was somewhat elaborated upon by the milpa (1) system of growing which also allowed (even encouraged) the growth of certain weeds (quelites) (2)

  1. The “Milpa” system is a traditional intercropping system of regional vegetables. Present day Mayan farmers cultivate this intercropping system through the practice of slash and burn together with small plots of other vegetable crops such as chiles, corn, beans, and squash. The Maya milpa entails a rotation of annual crops with a series of managed and enriched intermediate stages of short-term perennial shrubs and trees, culminating in the re-establishment of mature closed forest on the once-cultivated parcel. The milpa cycle involves two years of cultivation and eight years of fallow, or secondary growth, to allow for natural regeneration of vegetation. As long as this rotation continues without shortening fallow periods, the system can be sustained indefinitely. (
  2. See Post Quelites : Quilitl. I have written on many wild herbs/weeds that are edible/medicinal. As a herbalist these wild plants are my favourite allies.

Image via Maize intercropping in the milpa system. Diversity, extent and importance for nutritional security in the Western Highlands of Guatemala. (Lopez-Ridaura etal 2021)

One of my favourite plants in this category is a Tagetes species (1). The marigolds in this family are planted near my tomatoes (along with basil – Ocimum basilicum – which is also an allelopathic) which deters certain flying pests and the formation of nematodes (2) on the plants roots.

  1. the same species as cempasuchil. See the following Posts for more information on these plants. Cempasuchil; Huacatay Tagetes minuta; Quelite : Pericón : Tagetes lucida; Mexican Mint Marigold
  2. Root knot nematodes are tiny ‘eelworms’ that live in soil and become plant parasites when they use tomato roots as their nurseries. Often nematodes enter tomato roots through small injuries. As their numbers multiply, small feeder roots are destroyed, and irregular galls take their place. These parasites will stunt the growth of the tomato.
Tomato root knot nematodes

Below is a small selection of plants and their beneficial and detrimental neighbours

Visit for a more comprehensive companion plant list

So far we have only looked at allelopathy as it refers to plants affecting each others growth. How does allelopathy enter the realm of herbal medicine and the treatment of human pathologies? Allelopathy is mediated by allelochemicals. These chemicals are considered to be secondary metabolites. Secondary metabolites, also called specialised metabolites, toxins, secondary products, or natural products, are organic compounds produced by any lifeform, (bacteria, fungi, animals, or plants), which are not directly involved in the normal growth, development, or reproduction of the organism and it is these chemicals we utilise in herbal medicine. These chemicals can be used to treat everything from a runny nose to various forms of life threatening cancers.

Below is a short list (and the appropriate scientific studies) of some valuable medicinal plants rich in allelochemicals.

Digitalis (obtained from the dried leaves of the common foxglove – Digitalis purpurea – strengthens the contractions of the heart – it is a DANGEROUS remedy – all parts of the plants are poisonous if eaten) and Diosgenin (extracted from the tubers of Dioscorea wild yam species – helps protect against atherosclerotic diseases) to treat cardiovascular disease

  • Semwal, Prabhakar et al. “Diosgenin: An Updated Pharmacological Review and Therapeutic Perspectives.” Oxidative medicine and cellular longevity vol. 2022 1035441. 29 May. 2022, doi:10.1155/2022/1035441

Taxol (a plant alkaloid chemotherapeutic agent (“antineoplastic” or “cytotoxic”) derived from the bark of the Pacific yew tree (Taxus brevifolia) and Vinblastine (isolated from the leaves of the Madagascar periwinkle plant, Catharanthus roseus, formerly known as Vinca rosea) for cancer treatment. WARNING :  almost every part of the Yew tree is extremely poisonous. Very small amounts of bark, needles, seeds, or even the sap can be deadly enough to kill an adult (children need even less).

  • Weaver BA. How Taxol/paclitaxel kills cancer cells. Mol Biol Cell. 2014 Sep 15;25(18):2677-81. doi: 10.1091/mbc.E14-04-0916. PMID: 25213191; PMCID: PMC4161504.
  • Slichenmyer, William J; Von Hoff, Daniel D. Taxol: a new and effective anti-cancer drug. Anti-Cancer Drugs 2(6):p 519-530, December 1991.
  • von der Maase, H., Hansen, S. W., Roberts, J. T., Dogliotti, L., Oliver, T., Moore, M. J., … & Conte, P. F. (2000). Gemcitabine and cisplatin versus methotrexate, vinblastine, doxorubicin, and cisplatin in advanced or metastatic bladder cancer: results of a large, randomized, multinational, multicenter, phase III study. Journal of clinical oncology, 18(17), 3068-3077.

Colchicine for gout and Behçet’s disease (Behcet’s (beh-CHETS) disease, also called Behcet’s syndrome, is a rare disorder that causes blood vessel inflammation throughout your body. The cause of Behçet’s disease is unknown, although most experts believe it’s an autoinflammatory condition.) Colchicine is sourced from the Autumn crocus (Crocus autumnale also called Meadow Saffron) and has been used medicinally since at least 1500BC. It is an Old School herbal medicine that is potent but potentially (and very easily) poisonous. 7 to 26mg is enough to cause acute overdose. The plant is often misidentified with wild garlic and this error has resulted in numerous poisonings and intoxications.

  • Finkelstein Y, Aks SE, Hutson JR, Juurlink DN, Nguyen P, Dubnov-Raz G, et al. (June 2010). “Colchicine poisoning: the dark side of an ancient drug”. Clinical Toxicology. 48 (5): 407–414. doi:10.3109/15563650.2010.495348. PMID 20586571. S2CID 33905426.
  • Brvar, Miran et al. “Acute poisoning with autumn crocus (Colchicum autumnale L.).” Wiener klinische Wochenschrift vol. 116,5-6 (2004): 205-8. doi:10.1007/BF03040489

Batatasin for diabetes (Batatasins are endogenous plant hormones found in yams and other related plant species)

  • Naomi R, Bahari H, Yazid MD, Othman F, Zakaria ZA, Hussain MK. Potential Effects of Sweet Potato (Ipomoea batatas) in Hyperglycemia and Dyslipidemia-A Systematic Review in Diabetic Retinopathy Context. Int J Mol Sci. 2021 Oct 6;22(19):10816. doi: 10.3390/ijms221910816. PMID: 34639164; PMCID: PMC8509747.

Pinene, Cineole, and Eucalyptol in aromatherapy for non-purulent (no pus discharge) rhinosinusitis (inflammation of the nasal cavity and paranasal sinuses. The term “rhinosinusitis” is preferred over “sinusitis” because inflammation of the sinus cavities is almost always accompanied by inflammation of the nasal cavities)

  • Salehi B, Upadhyay S, Erdogan Orhan I, Kumar Jugran A, L.D. Jayaweera S, A. Dias D, Sharopov F, Taheri Y, Martins N, Baghalpour N, C. Cho W, Sharifi-Rad J. (2019) Therapeutic Potential of α- and β-Pinene: A Miracle Gift of Nature. Biomolecules.; 9(11):738.
  • Kehrl, Wolfgang et al. “Therapy for acute nonpurulent rhinosinusitis with cineole: results of a double-blind, randomized, placebo-controlled trial.” The Laryngoscope vol. 114,4 (2004): 738-42. doi:10.1097/00005537-200404000-00027
  • Nikhil Chandorkar;Srushti Tambe;Purnima Amin;Chandu Madankar; (2021). A systematic and comprehensive review on current understanding of the pharmacological actions, molecular mechanisms, and clinical implications of the genus Eucalyptus . Phytomedicine Plus, (), –. doi:10.1016/j.phyplu.2021.100089

Benzoxazinones for preterm labour (Benzoxazinoids (BXs) are secondary metabolites present in many Poaceae including the major crops maize, wheat, and rye.) Benzoxazinoids from Scoparia dulcis (sweet broomweed) have an antiproliferative activity against the DU-145 human prostate cancer cell line

  • Sicker, Dieter (2002). [Studies in Natural Products Chemistry] Bioactive Natural Products (Part H) Volume 27 || Benzoxazinones in plants: Occurrence, synthetic access, and biological activity. , (), 185–232. doi:10.1016/s1572-5995(02)80037-0
  • Niculaes, Claudiu; Abramov, Aleksej; Hannemann, Laura; Frey, Monika (2018). Plant Protection by Benzoxazinoids—Recent Insights into Biosynthesis and Function. Agronomy, 8(8), 143–. doi:10.3390/agronomy8080143
  • Wan-Hsun Wu; Tzu-Yu Chen; Rui-Wen Lu; Shui-Tein Chen; Chia-Chuan Chang (2012). Benzoxazinoids from Scoparia dulcis (sweet broomweed) with antiproliferative activity against the DU-145 human prostate cancer cell line. , 83(none), –. doi:10.1016/j.phytochem.2012.07.022

Rosmarinic acid for asthma and alzheimer’s disease. RA is found in mint, salvia, lemon balm, marjoram, oregano, rosemary, and other species in the Labiatae or Lamiaceae family of plants.

  • Liang Z, Xu Y, Wen X, Nie H, Hu T, Yang X, Chu X, Yang J, Deng X, He J. Rosmarinic Acid Attenuates Airway Inflammation and Hyperresponsiveness in a Murine Model of Asthma. Molecules. 2016 Jun 13;21(6):769. doi: 10.3390/molecules21060769. PMID: 27304950; PMCID: PMC6274450.
  • Hase, T., Shishido, S., Yamamoto, S. et al. Rosmarinic acid suppresses Alzheimer’s disease development by reducing amyloid β aggregation by increasing monoamine secretion. Sci Rep 9, 8711 (2019).

Thymol and its isomer Carvacrol for respiratory disorders and skin infection diseases. The main source of thymol is the herb thyme (Thymus vulgaris), it can also be found in savory of Crete (Satureja thymbra – also called Roman hyssop), bergamot (Monarda didyma – also called crimson beebalm and Oswego tea), star anise (Illicium verum), Oregano (Origanum vulgare), dittany of Crete (Origanum dictamnus) and Greek oregano (Origanum onites)

  • Karina Kachur & Zacharias Suntres (2020) The antibacterial properties of phenolic isomers, carvacrol and thymol, Critical Reviews in Food Science and Nutrition, 60:18, 3042-3053, DOI: 10.1080/10408398.2019.1675585

Baicalin, Scutellarin, Hesperetin, Nicotianamine, and Glycyrrhizin that their therapeutic properties have been identified previously in the treatment of SARS, and are herbal options for Covid-19 treatment protocols. These chemicals are found primarily in baical skullcap (Scutellaria baicalensis) and the European skullcap (Scutellaria lateriflora). Glycyrrhizin is sourced from the licorice (liquorice) plant Glycyrrhiza glabra.

  • Bakhshayeshan-Agdam, Hamideh & Lisar, Seyed Yahya & Razeghi, Jafar. (2020). Allelochemical therapeutic properties as natural bio-active compounds: A pharmacological approach.
  • Zandi, K., Musall, K., Oo, A., Cao, D., Liang, B., Hassandarvish, P., … & Schinazi, R. F. (2021). Baicalein and baicalin inhibit SARS-CoV-2 RNA-dependent-RNA polymerase. Microorganisms, 9(5), 893.
  • Li, Y., Wu, Y., Li, S., Li, Y., Zhang, X., Shou, Z., … & Li, L. (2022). Identification of phytochemicals in Qingfei Paidu decoction for the treatment of coronavirus disease 2019 by targeting the virus-host interactome. Biomedicine & Pharmacotherapy, 156, 113946.
  • Gomaa, A. A., & Abdel-Wadood, Y. A. (2021). The potential of glycyrrhizin and licorice extract in combating COVID-19 and associated conditions. Phytomedicine plus, 1(3), 100043.
  • Luo, P., Liu, D., & Li, J. (2020). Pharmacological perspective: glycyrrhizin may be an efficacious therapeutic agent for COVID-19. International Journal of Antimicrobial Agents55(6), 105995.

So, as you can see, there are some seriously medicinally active plants in this small sample group

Allelopathy therefore provides beneficial effects for both humans and plants. In the grand scheme of things it is a relatively newly defined herbal medicinal action. It is an ancient practice though and even though it may have had no specific designation these actions have been used for healing longer than we have been writing about medicinal herbs.


  • Aguilar Carrera, Sergio (2012); Método práctico de lengua náhuatl del Altiplano Mexicano; Amecameca variant, Dirección de Casa de Cultura de Tecámac, State of Mexico, Mexico. ISBN 03-2012-030812540200-01.
  • Bakhshayeshan-Agdam, Hamideh & Lisar, Seyed Yahya & Razeghi, Jafar. (2020). Allelochemical therapeutic properties as natural bio-active compounds: A pharmacological approach.
  • Camille Aubertin, Margot Archambeau, Jean-Pierre Sarthou, 2022. Allelopathy : Definition. Dictionnaire d’agroécologie.
  • Cheng F., Zhihui Cheng Z. 2015. Research Progress on the use of Plant Allelopathy in Agriculture and the Physiological and Ecological Mechanisms of Allelopathy. Frontiers in plant science, 6: 1020.
  • Conboy, Niall J. A.; McDaniel, Thomas; Ormerod, Adam; George, David; Gatehouse, Angharad M. R.; Wharton, Ellie; Donohoe, Paul; Curtis, Rhiannon; Tosh, Colin R.; Desneux, Nicolas (2019). Companion planting with French marigolds protects tomato plants from glasshouse whiteflies through the emission of airborne limonene. PLOS ONE, 14(3), e0213071–. doi:10.1371/journal.pone.0213071
  • Héctor Mancilla Sepúlveda (2002); Lecciones de Náhuatl, (dialecto de Amecameca), Editorial Hirata; Mexico City, Mexico.
  • Kato-Noguchi H, Kurniadie D. Allelopathy and Allelochemicals of Leucaena leucocephala as an Invasive Plant Species. Plants (Basel). 2022 Jun 24;11(13):1672. doi: 10.3390/plants11131672. PMID: 35807624; PMCID: PMC9269122.
  • Lopez-Ridaura, S., Barba-Escoto, L., Reyna-Ramirez, C.A. et al. Maize intercropping in the milpa system. Diversity, extent and importance for nutritional security in the Western Highlands of Guatemala. Sci Rep 11, 3696 (2021).
  • Marahatta SP, Wang KH, Sipes BS, Hooks CR. Effects of Tagetes patula on Active and Inactive Stages of Root-Knot Nematodes. J Nematol. 2012 Mar;44(1):26-30. PMID: 23482862; PMCID: PMC3593261.
  • Molisch, Hans (19 March 1938). “Der Einfluss einer Pflanze auf die Andere, Allelopathie”. Nature. 141 (3568): 493. doi:10.1038/141493a0.
  • Naomi R, Bahari H, Yazid MD, Othman F, Zakaria ZA, Hussain MK. Potential Effects of Sweet Potato (Ipomoea batatas) in Hyperglycemia and Dyslipidemia-A Systematic Review in Diabetic Retinopathy Context. Int J Mol Sci. 2021 Oct 6;22(19):10816. doi: 10.3390/ijms221910816. PMID: 34639164; PMCID: PMC8509747.
  • Rice, Elroy Leon (1984), Allelopathy, (first edition, november 1974 by the same editor) (Second ed.), Academic Press, pp. 422 p, ISBN 978-0-12-587058-0
  • Roger, Manuel Joaquín Reigosa; Reigosa, Manuel J.; Pedrol, Nuria; González, Luís (2006), Allelopathy: a physiological process with ecological implications, Springer, p. 1, ISBN 978-1-4020-4279-9
  • Watson, George (1938). Nahuatl Words in American English. American Speech, 13(2), 108–121. doi:10.2307/451954
  • Whittaker, R. H.; Feeny, P. P. (1971). “Allelochemics: Chemical Interactions between Species”. Science. 171 (3973): 757–770. Bibcode:1971Sci…171..757W. doi:10.1126/science.171.3973.757. ISSN 0036-8075. JSTOR 1730763. PMID 5541160
  • Willis RJ (2000) Juglans spp., juglone and alleopathy. Allelopathy Journal 7 (1) 1-55.
  • Willis, Rick J. (2007). The History of Allelopathy. Springer. p. 3. ISBN 978-1-4020-4092-4. Retrieved 2009-08-12.



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