Euphorbia trigona Mill. (1768) is a fast-growing succulent shrub or small tree from Central Africa that has become one of the most widely cultivated houseplants in the Euphorbia genus — yet paradoxically, it may never have existed in the wild. Known primarily from cultivation, never confirmed to flower, and possibly of hybrid origin, the African milk tree is a botanical enigma wrapped in a remarkably easy-to-grow package. Its distinctive three-angled stems, persistent teardrop-shaped leaves, and the wildly popular purple-red cultivar ‘Royal Red’ have made it a fixture of indoor plant collections worldwide. Commercially, Euphorbia trigona is so heavily traded that it has been specifically exempted from CITES regulation — one of only three Euphorbia species to receive this distinction.
Taxonomy and Nomenclature
Euphorbia trigona was named and described by the Scottish-born botanist Philip Miller in the eighth edition of The Gardener’s Dictionary, published in 1768. The specific epithet trigona comes from the Latin for “three-angled,” referring to the triangular cross-section of the stems — the species’ most immediately recognisable feature.
Within the genus Euphorbia, the species is classified in subgenus Euphorbia, section Euphorbia, alongside the large candelabra-forming African euphorbias. However, its placement in this group is not entirely straightforward given its unusual biology and uncertain wild provenance.
According to Plants of the World Online (POWO, Kew), Euphorbia trigona has one accepted synonym: Euphorbia hermentiana Lem. (1858), described by the French botanist Charles Lemaire in L’Illustration Horticole. The native range is given as Gabon to Malawi, encompassing Angola, Congo, the Democratic Republic of the Congo, Gabon, and Malawi. The species has been introduced to Bangladesh, India, and Tunisia.
Common names: African milk tree, African milk bush, cathedral cactus, candelabra cactus, Abyssinian euphorbia, friendship cactus, good luck cactus, high chaparral (Dreikantige Wolfsmilch in German, Cowboy-kaktus in Danish).
The Mystery of Origin: A Plant Known Only from Cultivation?
Perhaps the most intriguing aspect of Euphorbia trigona is the persistent uncertainty surrounding its wild origins. According to the Encyclopedia of Living Forms (LLIFLE) and multiple taxonomic references, the species is possibly of hybrid origin, as it is known primarily — and perhaps exclusively — from cultivation. The type specimen was said to originate from India, but the more likely geographic origin is Angola in Central Africa.
Several lines of evidence support the hypothesis that Euphorbia trigona may not exist as a truly wild species. The plant has never been known to flower in cultivation, a striking absence for a species that has been grown for over 250 years. While some anecdotal reports claim occasional flowering, no verifiable documentation exists. This sterility is consistent with hybrid origin, as interspecific hybrids in Euphorbia frequently display reduced or absent fertility.
In Central Africa, Euphorbia trigona is widely planted as a hedge and ornamental, which obscures the extent of genuinely wild populations. Some reports describe it growing in thickets and semi-arid savannas, but it remains unclear whether these represent native stands, naturalised escapes from cultivation, or ancient introductions that predate botanical documentation.
This unusual status makes Euphorbia trigona a “cultigen” — a plant known primarily through its long association with human cultivation rather than from wild populations — a designation it shares with other widely grown species whose exact wild ancestry remains debated.
Description and Morphology
Euphorbia trigona is a tender, evergreen succulent that develops into a densely branched, erect shrub or small tree reaching two metres or more indoors and up to 3.5 metres (approximately 12 feet) under ideal conditions. It produces multiple upright branches from the base, creating a compact, columnar silhouette that gives it its popular name “cathedral cactus.”
Stems
The stems are the plant’s defining feature: triangular in cross-section (three-winged), segmented, and dark green with distinctive V-shaped lighter green patterns along the faces. The angles are more or less winged, with prominent teeth spaced approximately one centimetre apart. The stems are succulent, storing water efficiently, and are covered by thin, smooth, green bark that gradually turns grey to brownish with age.
This three-sided architecture is unique among the commonly cultivated tree euphorbias and immediately distinguishes Euphorbia trigona from four- to eight-ribbed species like Euphorbia ammak, Euphorbia ingens, and Euphorbia abyssinica.
Spines
The spines are paired, reddish-brown darkening to grey with age, and measure 5 to 6 mm long. They are arranged along the ridges of the stems, with leaves emerging from between each pair of spines.
Leaves
Unlike most arborescent euphorbias, Euphorbia trigona produces conspicuous, persistent leaves — a character that immediately sets it apart. The leaves are obovate to elliptical (teardrop-shaped), measuring 2 to 5 cm long and up to 1.5 cm wide, with entire margins. They grow along the branch ribs from between the paired spines on each ridge, giving the plant a leafier, less austere appearance than its larger candelabra relatives.
The leaves are typically deciduous, dropping in winter under conditions of reduced light and cooler temperatures, then regenerating in spring. However, in consistently warm, bright, indoor conditions — particularly without direct sunlight — leaves may persist for several years.
Flowers and Fruits
Euphorbia trigona has never been reliably documented to flower in cultivation. In theory, the flowers would be small cyathia typical of the genus, green to yellow in colour, surrounded by bracts. The reported absence of flowering over centuries of cultivation is one of the strongest arguments for the species’ possible hybrid origin. The fruit, when described from wild-origin material, is a dull red schizocarp measuring 5–6 mm by 12–15 mm, with light brown to white, smooth seeds approximately 3.5 × 3 mm.
The ‘Royal Red’ Cultivar
Euphorbia trigona ‘Royal Red’ (also marketed as Euphorbia trigona f. rubra, Euphorbia trigona ‘Rubra’, or simply “Red African Milk Tree”) is the most commercially significant cultivar and arguably one of the most popular succulent houseplants of the 2020s.
Characteristics
‘Royal Red’ is selected for its ability to develop deep burgundy to magenta colouration on stems and leaves when grown in sufficient light. The anthocyanin pigments responsible for this red-purple flush intensify under bright conditions, particularly in direct or near-direct sunlight, and fade back toward green in lower light — a reversible process that serves as a visual indicator of light adequacy.
The stems display a bicoloured look: the body of the stem often retains more green tones while the rib margins, spine bases, and leaves flush rich magenta-red. Some specimens develop an almost entirely purple-red appearance, while others remain predominantly green with red accents. The V-shaped patterning on the stem faces takes on a bronzish-green to purple-red hue.
Cultivar versus Variety
‘Royal Red’ is a cultivar (cultivated variety), not a hybrid. It originated as a somatic mutation — a spontaneous change in the DNA of the cells of a single plant — rather than through crossing with another species. All ‘Royal Red’ plants in circulation are vegetatively propagated from this original mutant or its descendants, which explains the high degree of uniformity in the clone. The care requirements are identical to those of the standard green Euphorbia trigona.
CITES Status: A Rare Exemption
Euphorbia trigona holds a distinctive regulatory position. While all succulent Euphorbia species are listed under CITES Appendix II, the current CITES annotation explicitly states that:
“Artificially propagated specimens of cultivars of Euphorbia trigona […] are not subject to the provisions of the Convention.”
This means that cultivated Euphorbia trigona — including ‘Royal Red’ and all other cultivars — can be traded internationally without CITES permits, provided the specimens are recognisably artificially propagated. This exemption, which took effect on 18 September 1997, was introduced to reduce the administrative burden on management authorities, since the species is propagated on an industrial scale and is not collected from the wild for international trade.
Euphorbia trigona shares this privileged status with only two other Euphorbia taxa: Euphorbia lactea (crested, fan-shaped, or colour mutants grafted on Euphorbia neriifolia rootstock) and Euphorbia milii (when traded in shipments of 100 or more artificially propagated specimens). The trade volume justifying this exemption is substantial: CITES trade records documented 228,126 specimens of Euphorbia trigona traded internationally between 1995 and 1999 alone, placing it among the most heavily commercialised euphorbia species globally.
Phytochemistry and Traditional Uses
Traditional Medicine
In its Central African range and in India (where the species has been introduced and widely naturalised), Euphorbia trigona has traditional medicinal applications. In the Ayurvedic system, the latex has been used as an agent against urinary tract infections. In other traditional practices, the leaves are applied as a poultice for the treatment of boils, and the milky sap has been used to treat earaches. The plant has also been employed traditionally for muscle swelling, allergies, and psoriasis.
Phytochemical Profile
Phytochemical investigations have revealed a diverse secondary metabolite profile. A 2022 study from the Jawaharlal Nehru Tropical Botanic Garden and Research Institute (India) isolated and characterised six compounds from Euphorbia trigona: epi-friedelinyl acetate, 3β-friedelinol, taraxerol, rhoiptlenone, stigmasterol, and stearic acid — with epi-friedelinyl acetate, rhoiptlenone, and stearic acid reported for the first time from this species. The major triterpenoids quantified by HPTLC were 3β-friedelinol (0.91% dry weight) and taraxerol (1.45% dry weight).
A broader phytochemical review identified 16 compounds from Euphorbia trigona, spanning triterpenoids (lupane, oleanane, and phorbol-type), phenolic compounds (gallic acid and ellagic acid derivatives, flavonoids), phytosterols, and glycosides. A 2025 study using supercritical fluid CO₂ extraction identified high concentrations of rosmarinic acid, gallic acid, daidzein, ellagic acid, naringenin, and ferulic acid, and demonstrated anti-yeast, anticancer (MTT assay), wound healing, and anti-obesity (lipase inhibition) activities in vitro.
Importantly, cytotoxicity testing of Euphorbia trigona plant and latex extracts against human cervical cancer (HeLa) cells showed insignificant cytotoxic effects up to 100 μg/ml concentration, while being non-toxic to the normal cardiac myoblast cell line (H9C2). This relatively mild cytotoxic profile contrasts with the more potent activity documented for euphol-rich species like Euphorbia tirucalli and Euphorbia ammak.
⚠ Critical safety disclaimer — the latex is toxic regardless of its medicinal history. Despite traditional medicinal uses, the white latex of Euphorbia trigona is an irritant and a poison. Contact with skin causes dermatitis and chemical burns; contact with eyes can result in severe keratoconjunctivitis and potential vision damage. Ingestion causes intense inflammation of the digestive tract. Under no circumstances should the latex or any part of the plant be used for self-medication. Traditional uses reflect historical practices that did not benefit from modern toxicological knowledge, and the gap between ethnobotanical use and safe, evidence-based medicine is vast. All handling of Euphorbia trigona should involve gloves and eye protection, and contact with the sap should be immediately rinsed with cold water.
Cultivation and Care
Euphorbia trigona is one of the easiest large succulents to grow, tolerating a wider range of indoor conditions than most arborescent euphorbias. Its rapid growth — gaining 30 to 60 cm per year under good conditions — and dramatic silhouette make it an ideal statement plant for bright interiors.
Light
Bright, indirect light is the minimum; full sun produces the best growth, colouration (particularly for ‘Royal Red’), and spine development. At least four to six hours of direct or bright filtered sunlight per day is recommended. In insufficient light, stems become etiolated (stretched and pale), spines shorten, and the red cultivar reverts to green.
A south-facing window is ideal in the Northern Hemisphere. In summer, the plant can be moved outdoors to a gradually acclimated sunny position. Be aware that sudden exposure to intense sunlight after indoor overwintering can cause stem scorch.
Temperature
Euphorbia trigona prefers warmth: the ideal range is 18–30 °C, and it tolerates high summer temperatures without difficulty. It is not frost-hardy — prolonged exposure below 5 °C causes damage, and any frost is potentially fatal. In USDA zones 10b to 11b (marginal in zone USDA 10a), it can be grown outdoors year-round. In cooler climates, it must be brought indoors for winter. It should never be placed near cold draughts or single-pane windows in winter.
Watering
Water thoroughly during the growing season (spring through autumn) when the top 2–3 cm of soil has dried completely. In winter, reduce watering significantly — once monthly or less — allowing the substrate to dry almost entirely between irrigations. Euphorbia trigona stores water efficiently in its succulent stems and tolerates moderate drought, but overwatering causes root rot, the single most common cause of death.
Substrate
A well-draining mix is essential. A standard cactus and succulent blend amended with extra perlite, pumice, or coarse sand (50–60% mineral fraction) works well. The species is not fussy about pH (tolerates mildly acidic to mildly alkaline). Good drainage is far more important than nutrient content.
Fertilisation
Feed monthly with a balanced, half-strength liquid fertiliser during the active growing season. Do not fertilise during winter dormancy.
Propagation
Euphorbia trigona propagates effortlessly from stem cuttings, which is the universal method given that the plant does not flower or set seed. Cut a branch or segment, rinse the cut end with cold water to stop latex flow, allow it to callus for several days to a week in a dry, shaded location, then plant in dry, well-draining substrate. Roots typically establish within two to four weeks. Rooting hormone is helpful but not required.
Safety reminder: always wear gloves and eye protection when cutting. The latex flows freely and is highly irritant.
The Toppling Problem
One well-known challenge with mature Euphorbia trigona is its tendency to become top-heavy and fall over. The plant develops a surprisingly shallow and compact root system relative to its height, creating an imbalanced centre of gravity as the branching crown grows. Heavy clay or ceramic pots provide better stability than lightweight plastic containers. Staking may be necessary for tall specimens, and periodic pruning of top-heavy branches reduces the risk of the entire plant toppling — a particularly messy event given the copious latex release.
Pests and Diseases
Euphorbia trigona is essentially pest-free. Mealybugs and scale insects can occasionally appear but are rarely serious. Root rot from overwatering remains the primary threat. In outdoor settings, strong winds can damage the brittle columns.
Landscape and Interior Design Uses
In frost-free climates (USDA zones 10–11), Euphorbia trigona makes an excellent hedge, screen, or architectural accent — a traditional use in its Central African range. Its dense branching and spiny stems create an effective living barrier.
As an indoor plant, it serves as a dramatic vertical element in bright rooms, offices, atriums, and sunrooms. The ‘Royal Red’ cultivar is particularly prized for adding colour to predominantly green succulent collections. Group plantings of green and red forms create striking colour contrasts.
The species is also widely grown in container culture on patios and balconies during the warm season, moved indoors for winter. Its relatively narrow footprint makes it suitable for spaces where floor area is limited but vertical height is desired.
Sources
- Miller, P. (1768). The Gardener’s Dictionary, ed. 8, n° 3. [Original species description]
- Lemaire, C. (1858). Euphorbia hermentiana. L’Illustration Horticole 5 (Misc.): 63. [Synonym]
- Govaerts, R., Frodin, D.G. & Radcliffe-Smith, A. (2000). World Checklist and Bibliography of Euphorbiaceae (and Pandaceae) 1–4: 1–1622. The Board of Trustees of the Royal Botanic Gardens, Kew.
- Carter, S. & Eggli, U. (2003). The CITES Checklist of Succulent Euphorbia Taxa, 2nd edition. Federal Agency for Nature Conservation, Germany.
- Anju, V. & Rameshkumar, K.B. (2022). Phytochemical investigation of Euphorbia trigona. Industrial Crops and Products 178: 114620.
- Bazaid, A.S. et al. (2025). Unveiling the in vitro activity of extracted Euphorbia trigona via Supercritical Fluid Extraction against pathogenic yeasts, obesity, cancer, and its wound healing properties. Bioresources and Bioprocessing 12: 28.
- Kemboi, D. et al. (2020). A review of the ethnomedicinal uses, biological activities, and triterpenoids of Euphorbia species. Fitoterapia 154: 104750.
- Amtaghri, S. et al. (2022). Traditional uses, pharmacological, and phytochemical studies of Euphorbia: a review. Current Topics in Medicinal Chemistry 22(19): 1553–1576.
- Mavundza, E.J. et al. (2025). Pharmacological significance, medicinal use, and toxicity of extracted and isolated compounds from Euphorbia species found in Southern Africa: a review. Plants 14(3): 469.
Authority Pages
- POWO — Plants of the World Online, Royal Botanic Gardens, Kew: Euphorbia trigona Mill.
- CITES — Convention on International Trade in Endangered Species: Euphorbia trigona — Appendix II with explicit exemption for artificially propagated cultivars
- GBIF — Global Biodiversity Information Facility: Euphorbia trigona Mill.
- IPNI — International Plant Names Index: Euphorbia trigona Mill.
- LLIFLE — Encyclopedia of Living Forms: Euphorbia trigona
- NC State Extension — North Carolina Extension Gardener Plant Toolbox: Euphorbia trigona
- Wikispecies: Euphorbia trigona