Euphorbia tirucalli is a succulent tree native to eastern and southern Africa that has become one of the most widely cultivated ornamental species in the genus Euphorbia. Known by a bewildering array of common names — pencil cactus, pencil tree, firestick plant, milk bush, Indian tree spurge — this spineless, tree-like euphorbia is prized for its extraordinary architectural form: dense masses of smooth, cylindrical, pencil-thin green branches that glow vivid orange and red in cool weather. It is also one of the most dangerous plants commonly sold in garden centres, with a latex so caustic that a single splash in the eye can cause temporary blindness and send the victim to the emergency room. A member of the family Euphorbiaceae, Euphorbia tirucalli has been investigated as a biofuel crop, used as a traditional fish poison across Africa, and controversially promoted — then debunked — as an anti-cancer remedy.
Taxonomy and Nomenclature
Euphorbia tirucalli was described by Carl Linnaeus in 1753 in Species Plantarum (volume 1, page 452). The species is classified within the subgenus Euphorbia.
The specific epithet tirucalli is not Latin but borrowed from tirukalli, the name used by the inhabitants of Malabar (Kerala, southern India), where the plant was widely cultivated at the time of its description. This is one of the rare cases in the genus where Linnaeus adopted a vernacular name directly as the scientific epithet.
Synonyms (POWO — 18 synonyms recorded): The most commonly encountered include Euphorbia media N.E.Br., Euphorbia scoparia N.E.Br., Euphorbia viminalis Mill., and Tirucalia indica Raf. The full synonymy reflects the species’ extraordinarily wide distribution and long history of cultivation, which led to multiple independent descriptions from different regions.
Common names: pencil cactus, pencil tree, firestick plant, fire sticks, milk bush, milk hedge, Indian tree spurge, rubber hedge euphorbia, naked lady, petroleum plant (English); kraalmelkbos (Afrikaans); arbre de Saint-Sébastien, euphorbe effilée (French); Bleistiftstrauch, Milchbusch (German); 绿玉树, lü yu shu (Chinese).
Description
Euphorbia tirucalli is a large, unarmed (spineless), succulent shrub or small tree that can reach 5 to 7 m in cultivation and up to 12–15 m in its native African habitat.
Trunk and Branches
The plant develops one or several woody main trunks with brown, rough bark. The crown is dense and rounded, composed of an extraordinary profusion of smooth, cylindrical, pencil-thick succulent branches (5–8 mm in diameter) that are the plant’s most distinctive feature. These branches are bright green, finely striated longitudinally, and arranged in whorls or brush-like masses at the tips of older stems. The overall effect is coral-like — a living sculpture of densely packed green pencils.
The ‘Sticks on Fire’ Colour Change
The cultivar Euphorbia tirucalli ‘Sticks on Fire’ (also sold as ‘Rosea’ or ‘Firesticks’) is the form most commonly seen in the horticultural trade. Its stems undergo a spectacular seasonal colour change: during cooler months and under intense sunlight, the normally green branches turn vivid shades of orange, red, and coral pink. This colour intensifies with cold stress, full sun exposure, and mild drought — the very conditions that would stress most other plants. In warm, shady conditions the plant reverts to green. This is not a separate species or even a distinct botanical variety: it is a naturally occurring colour form that appeared in the wild and was selected for cultivation. The Illustrated Handbook of Succulent Plants lists it under Euphorbia tirucalli without varietal rank.
Leaves
The leaves are tiny (1–2.5 cm long, 3–4 mm wide), oval, and ephemeral — appearing briefly at the tips of growing shoots before falling quickly. For most of the year, the plant is effectively leafless. Photosynthesis is performed primarily by the green stem tissue, using a remarkable dual photosynthetic system: the stems employ Crassulacean acid metabolism (CAM), while the transient leaves use the standard C3 pathway. This combination allows the plant to maintain carbon fixation even under extreme aridity — the CAM stems fix CO₂ at night with minimal water loss, while the C3 leaves maximise carbon gain during the brief humid periods when they are present.
Flowers and Fruit
Small, yellowish cyathia appear in clusters at the branch tips, mainly during the cooler months. They attract butterflies, bees, and other insects. The fruit is a fuzzy, pinkish, three-lobed capsule approximately 12 mm in diameter that splits explosively when ripe to eject its seeds.
Latex
When any part of the plant is damaged, Euphorbia tirucalli exudes a copious, milky-white latex that is extremely toxic and caustic. This latex is arguably the most dangerous aspect of this otherwise easy-going plant (see Toxicity and Safety Precautions).
Distribution and Habitat
According to POWO, Euphorbia tirucalli is native to Angola, the Democratic Republic of the Congo, Mozambique, Rwanda, South Africa (KwaZulu-Natal), Eswatini, Tanzania, and Zambia. Its presence in numerous other countries — including Eritrea, Ethiopia, Ghana, Somalia, South Sudan, Sudan, India, Indonesia, China, the Philippines, Australia, Madagascar, and much of tropical America — reflects a very long history of human introduction and subsequent naturalisation. The species has been traded, planted, and spread along maritime and caravan routes for centuries, making it virtually impossible to determine where it is truly native and where it was introduced.
In its natural habitat, Euphorbia tirucalli grows in semi-arid tropical climates at altitudes from sea level to approximately 2,000 m. It occurs in open savanna, thin woodland, grassy hills, rocky outcrops, and along watercourses. It often forms dense thickets and may produce hedge-like barriers in the veld.
A Dual-Purpose Plant: Biofuel Potential
Euphorbia tirucalli has attracted serious interest as a biofuel crop for semi-arid tropical regions. The rationale is compelling: the plant’s unique CAM + C3 photosynthetic combination allows it to produce substantial biomass on marginal land with minimal water input. The latex is rich in terpenoid hydrocarbons (primarily the C30 triterpenoid euphorol) that can be cracked into high-octane fuel.
Estimates suggest that Euphorbia tirucalli plantations could yield 10 to 20 tonnes of dry matter per hectare per year, from which approximately 1 to 2 tonnes of crude hydrocarbon oil could be extracted — equivalent to roughly 100 barrels per hectare annually. The residual fibrous biomass can be converted to gas, solid fuel (pellets, briquettes, charcoal), or paper pulp. The gross energy value of the biomass is approximately 17,600 kJ/kg.
In Venezuela and Colombia, Euphorbia tirucalli is already cultivated as a biofuel crop on a significant scale. The advantage is that the species thrives on land too dry and poor for conventional agriculture, offering economic potential for currently disadvantaged regions. However, large-scale commercial exploitation has not yet materialised in most countries, partly due to the challenges of handling the caustic latex at industrial scale.
Ethnobotanical Uses
Fish Poison
Across eastern and southern Africa, cut branches of Euphorbia tirucalli are thrown into rivers and pools to stun or kill fish. The latex disperses in the water and acts as a potent ichthyotoxin. This ancient practice is documented in multiple countries and cultures but is now largely restricted by conservation legislation.
Living Fence
One of the most widespread traditional uses: Euphorbia tirucalli is planted as a living hedge around homesteads, livestock pens, and cultivated fields throughout Africa and India. The dense, interlocking branches form an impenetrable barrier, and the toxic latex deters both human intruders and browsing animals. The common names “rubber hedge euphorbia” and “kraalmelkbos” (Afrikaans for “kraal milk bush”) reflect this use.
Traditional Medicine — And a Dangerous Myth
Euphorbia tirucalli has been used in traditional medicine across Africa, India, Indonesia, Malaysia, and Brazil for an extraordinary range of conditions, including warts, coughs, asthma, earache, rheumatism, toothache, and even as an alleged treatment for cancer and tumours.
The anti-cancer claim has been conclusively debunked. Research has demonstrated that Euphorbia tirucalli latex actually suppresses the immune system, promotes tumour growth, and is associated with the development of Burkitt’s lymphoma — a cancer of the lymphatic system prevalent in regions of Africa where the plant is abundant. The latex contains phorbol esters that act as potent tumour promoters (co-carcinogens). Far from curing cancer, Euphorbia tirucalli is now considered a cofactor in the disease. Self-medication with this plant’s latex is extremely dangerous and should be firmly discouraged.
Other Uses
The wood is white, close-grained, and moderately hard. It is used in Africa for roof struts, toys, and veneers. The latex has also been used as a fixative (for attaching knife blades to handles and spearheads to shafts) and as an insect repellent — the plant is reputed in Africa to deter mosquitoes and ants.
Cultivation
Euphorbia tirucalli is one of the easiest and fastest-growing large succulents in cultivation. It thrives on neglect, rewards full sun with spectacular colour (in the ‘Sticks on Fire’ form), and can grow 50 cm or more per year under good conditions.
Light
Full sun. The species requires maximum light exposure for compact growth and, in the ‘Sticks on Fire’ cultivar, for the most intense colour development. In insufficient light, the plant etiolates rapidly, producing thin, weak, pale branches. Indoors, place it in the brightest position available — a south- or west-facing window with direct sunlight for at least 5–6 hours per day.
Soil
Well-drained substrate is essential. A standard cactus and succulent mix, or a 2:1:1 blend of potting soil, perlite, and coarse sand, works well. The species is tolerant of a wide range of soil types in the ground, including clay soils common in southern California, provided drainage is adequate.
Watering
Highly drought-tolerant once established. During the growing season (spring through autumn), water when the top few centimetres of soil are completely dry — typically every 2 to 3 weeks. In winter, reduce watering to once a month or less. Overwatering is the most common cause of failure, leading to root rot that can kill large specimens surprisingly quickly.
Temperature and Hardiness
Euphorbia tirucalli is a tropical species with limited frost tolerance. It is significantly more cold-sensitive than species from the South African Cape like Euphorbia resinifera or Euphorbia enopla.
Anglophone grower reports (California, Arizona):
On DavesGarden, a grower in Peoria, Arizona, reported catastrophic damage after a short cold snap with overnight temperatures in the -1 to -2 °C (27–30 °F) range: all stems turned white and began falling off the branches, with bark discolouration. The grower questioned whether the twenty plants around the yard would survive at all. Another DavesGarden contributor noted that their pencil cactus survived a freak Christmas snowfall in 2005 with the loss of a few limbs, but bounced back because the cold did not persist. On Houzz, a grower observed that even mild nights around 3 °C (37 °F) caused tip die-back: shrivelling and blackening of branch tips that had to be cut away. The consensus from experienced California growers: the species is best suited to USDA zones 10 to 11 for permanent outdoor planting.
Francophone grower reports (France):
On CactusPro, the species is unanimously treated as a frost-intolerant houseplant in France. The encyclopaedia entry states: “rated as occasionally surviving -2 °C, but avoid dropping below 7 °C.” A contributor (ericdumans) reported that an unheated veranda that remained around 10 °C during winter was nearly fatal for his Euphorbia tirucalli: “I didn’t see much left of the tirucalli. It came back from the base in spring, but it had a close call.” On the Hivernage (Overwintering) thread, experienced collectors in Strasbourg explicitly list Euphorbia tirucalli among the species they do not risk leaving in their cold greenhouse, even when other euphorbias survive at 5 °C. On Au Jardin, a French contributor reported that their plant “froze this winter” when left outdoors, but was successfully propagated from cuttings taken from surviving tissue and placed in water — demonstrating the species’ remarkable ability to regenerate, but also confirming that outdoor exposure to French winters is lethal.
Synthesis — practical cold hardiness guidelines:
- Absolute minimum: approximately -2 °C (28 °F) for a very brief period, dry conditions. Even at this threshold, severe tip damage is virtually guaranteed and entire stems may be lost.
- Recommended winter minimum: 7 to 10 °C (45–50 °F). Below this range, growth stops and the risk of progressive cold damage increases sharply.
- Recommended USDA zones: 10b to 11 for permanent outdoor cultivation. Zone 10a is marginal; zone 9b is incompatible with long-term outdoor cultivation of this species.
- The zone 9b verdict: Euphorbia tirucalli should not be planted in the ground in zone 9b. Unlike Euphorbia balsamifera, which has demonstrated survival in favourable zone 9b microclimates (e.g., the Domaine du Rayol in Var), Euphorbia tirucalli has no comparable track record in continental Europe. Every cold snap below 0 °C will cause disfiguring damage, and a single night below -3 °C will likely kill the plant outright.
- For European growers: This is strictly an indoor or greenhouse plant in all of mainland Europe. It can be placed outdoors from June to September, then must be overwintered in a bright, frost-free room at 10–15 °C. In a cool veranda (8–10 °C), keep it completely dry to minimise rot risk.
Propagation
Euphorbia tirucalli is extremely easy to propagate by stem cuttings:
- Cut a healthy branch section (15–30 cm).
- Immediately plunge the cut end into cold water for 10–30 minutes to coagulate the latex and produce a clean wound.
- Allow the cutting to dry and callus in a shaded, dry location for 7–10 days.
- Plant in well-drained cactus mix and water sparingly until roots establish — typically 3 to 6 weeks in warm conditions.
Propagation by seed is possible but rarely practised, as cuttings are so efficient.
Pests and Diseases
Few problems. The toxic latex deters most insects and herbivores. Potential issues include:
- Root rot: The primary disease risk, caused by overwatering or poorly drained soil.
- Mealybugs and spider mites: Occasional pests, particularly on indoor specimens.
- Cold damage progressing to rot: After frost injury, damaged tissue softens and rots. The rot can spread into healthy tissue if not removed promptly (see below).
Toxicity and Safety Precautions
Euphorbia tirucalli has one of the most dangerous latexes of any commonly cultivated plant. It flows copiously from the slightest wound, and its effects are far more severe than many growers expect from a plant sold casually at Home Depot or Jardiland.
Routes of exposure and effects:
- Eyes: This is the most serious risk. A single splash of latex in the eye causes immediate, excruciating pain, severe keratitis (corneal inflammation), copious tearing, and temporary blindness that can last days to weeks. Multiple reports on DavesGarden describe emergency room visits after accidental eye contact during pruning. One detailed account describes a grower whose wife caught a drip from a severed branch in her eye while rotating the pot — pain lasted weeks and poison control warned of potential effects lasting up to 8 weeks. Eye exposure from Euphorbia tirucalli is a medical emergency requiring immediate hospital attention.
- Skin: The latex causes irritation, redness, and blistering on prolonged contact. Some individuals experience severe allergic reactions.
- Ingestion: Burns to mouth, lips, tongue, and throat. Nausea, vomiting, diarrhoea.
Mandatory precautions:
- Always wear sealed goggles (not just glasses) and thick gloves when pruning, repotting, or handling the plant.
- Wear a long-sleeved shirt — latex drips downward when cutting stems at height and can run along arms to exposed skin.
- Never use a chainsaw or power tools. These aerosolise the latex into a dangerous mist. Use hand tools only.
- After cutting, plunge the wound end into cold water to coagulate the latex and stop the flow.
- Wash hands and all tools thoroughly with soap and water after any contact.
- Keep the plant away from children, pets, and high-traffic areas.
- If latex enters the eyes, flush immediately with copious clean water for at least 15 minutes and seek emergency medical care.
Pruning a Large Specimen — Specific Risks
Euphorbia tirucalli is a fast grower that can reach 2 m indoors in a few years, often requiring pruning to control size. This is the most common scenario for latex accidents. The latex flows freely and in large volume from each cut — far more than most growers anticipate. When cutting overhead branches, gravity ensures the sap drips directly toward the face. Always have a second person present when pruning a large specimen, in case of an eye splash requiring immediate flushing.
Removing Frost-Damaged Branches
After a freeze, damaged stems soften, blacken, and may begin to rot. As with Euphorbia ingens, wait for warm, dry conditions before cutting. Remove all affected tissue well below the visibly damaged zone, into firm green tissue. Apply sulphur or copper-based fungicide to the wound. Damaged tissue still contains latex — handle with full protective gear.
Conservation Status
Euphorbia tirucalli is not threatened. It is one of the most widely distributed and abundantly naturalised Euphorbia species in the tropics. Like all succulent Euphorbia species, it is listed on CITES Appendix II, though cultivated specimens of Euphorbia tirucalli are exempted from CITES provisions since 18 September 1997, reflecting its extreme abundance in cultivation worldwide.
FAQ
Is Euphorbia tirucalli a cactus?
No. Despite being universally called “pencil cactus,” it is a member of the family Euphorbiaceae, not Cactaceae. Key differences: milky toxic latex (absent in cacti), no areoles, no cactus-type spines, and the characteristic cyathium floral structure of Euphorbia.
Why does my ‘Sticks on Fire’ turn green?
Colour loss in the ‘Sticks on Fire’ cultivar is caused by insufficient light and/or warm temperatures. The orange-red pigmentation is a stress response triggered by cool temperatures, bright direct sun, and moderate drought. Move the plant to a sunnier position and reduce watering to encourage colour return.
Can Euphorbia tirucalli cure cancer?
No — and the opposite is true. Research has demonstrated that the latex promotes tumour growth, suppresses immune function, and is a cofactor in Burkitt’s lymphoma. Self-medication with Euphorbia tirucalli latex is dangerous and should never be attempted.
How fast does Euphorbia tirucalli grow?
Very fast for a succulent. Outdoors in warm climates, it can grow up to 50 cm per year. One CactiGuide forum member reported growth of 1.3 m in 14 months from a small potted cutting. Indoors, growth is slower but still vigorous with adequate light and watering.
Is Euphorbia tirucalli invasive?
In some tropical regions, particularly in parts of Australia, the Caribbean, and the Pacific, Euphorbia tirucalli has naturalised and can become locally invasive. In temperate climates, frost prevents any invasive potential.
Key Takeaways
Euphorbia tirucalli is a plant of extraordinary contradictions: spectacularly beautiful yet dangerously toxic, effortlessly easy to grow yet capable of sending its owner to the emergency room. Its unique dual photosynthesis, its potential as a biofuel crop for arid lands, and the cautionary tale of its debunked cancer cure make it one of the most scientifically interesting species in a genus of over 2,000. For growers who respect its latex and provide it with warmth and light, the pencil cactus rewards with one of the most striking architectural forms in the succulent world.
Sources and References
- Plants of the World Online (POWO), Royal Botanic Gardens, Kew — Euphorbia tirucalli L. Accepted name.
- Mwine, J.T. & Van Damme, P. (2011). “Euphorbia tirucalli L. (Euphorbiaceae): the miracle tree: current status of available knowledge.” Scientific Research and Essays, 6(23): 4905–4914.
- South African National Biodiversity Institute (SANBI), PlantZAfrica — Euphorbia tirucalli.
- Voigt, W. & Porter, H. (2007). “Euphorbia tirucalli.” Plants of South Africa.
- CactusPro, Encyclopédie — Euphorbia tirucalli Linné 1753.
- Valadez-Vega, C. et al. (2015). “The role of Euphorbia tirucalli as a co-factor in Burkitt lymphoma.” World Journal of Clinical Cases, 3(1): 1–7.