Euphorbia ammak Schweinf. (1899) is a massive succulent tree endemic to the western Arabian Peninsula, where it stands as the sole large candelabra-forming Euphorbia native to the region. Often called the African candelabra or giant milk bush, this imposing species reaches ten metres in height and develops a striking silhouette of erect, four-ribbed branches that has captivated succulent collectors worldwide. Listed as Vulnerable on the IUCN Red List and regulated under CITES Appendix II, Euphorbia ammak occupies a unique biogeographical niche at the eastern fringe of the genus’s African radiation. Its latex contains euphol, a tetracyclic triterpene with documented anticancer activity, while its variegated cultivar ranks among the most misidentified large euphorbias in commercial horticulture.
Taxonomy and Nomenclature
Euphorbia ammak was described by the German-Baltic botanist and explorer Georg August Schweinfurth in 1899, in the Bulletin de l’Herbier Boissier (volume 7, appendix 2, page 319). The specific epithet ammak is derived from the local Arabic vernacular name for the plant in Yemen and the Hejaz region of Saudi Arabia.
Within the genus Euphorbia, the species is classified in subgenus Euphorbia, section Euphorbia — the large clade that unites the succulent, spiny, candelabra-forming species sometimes informally known as “tree euphorbias.” This placement allies Euphorbia ammak with well-known African candelabra species such as Euphorbia ingens, Euphorbia abyssinica, Euphorbia candelabrum, and Euphorbia cooperi.
According to Plants of the World Online (POWO, Kew), Euphorbia ammak has zero accepted synonyms — a remarkably clean nomenclatural history for a tree euphorbia. The native range is given as western Saudi Arabia and northern Yemen.
Common names: African candelabra, giant milk bush, candelabra spurge, desert cactus.
Description and Morphology
Euphorbia ammak is a large, tree-like succulent that forms a short, stout trunk crowned by an ascending framework of erect to slightly curved branches, creating the characteristic candelabra outline. In its native habitat, mature specimens attain heights of eight to ten metres.
Stems and Ribs
The branches are thick, dark green, and divided by four wing-like ribs — a diagnostic character that remains remarkably constant across populations. This is a key identification feature: while Euphorbia abyssinica develops five to eight ribs on mature branches and Euphorbia ingens shows four to five ribs with a tendency toward five, Euphorbia ammak maintains four ribs with great consistency. The branches reach a diameter of 12 to 15 cm, with relatively thin walls compared to the more massive Euphorbia ingens.
The rib margins are undulate (wavy), bearing teeth spaced approximately one centimetre apart. This wavy margin is another useful distinction from Euphorbia abyssinica, whose ribs tend to be straighter-edged.
Spines and Spine Shields
The spines are paired, brown, horn-shaped, and up to one centimetre long, emerging from obtriangular (inverted-triangular) spine shields that stand individually along the ribs. This spine shield morphology constitutes one of the most reliable characters for separating Euphorbia ammak from Euphorbia ingens, which possesses circular spine shields. The spines tend to diminish or disappear on very old stems.
Leaves
In favourable conditions — particularly when warmth and humidity coincide — simple, lanceolate leaves appear near the growing tips of branches. On seedlings, these leaves reach up to 40 mm long and 7 mm wide; on older plants, the leaves are smaller and deciduous, persisting only briefly before falling naturally.
Flowers and Fruits
Euphorbia ammak produces solitary, subsessile cyathia above the pairs of spines. The flowers are yellow-green, fleshy, and approximately one centimetre in diameter. Flowering can occur year-round in tropical climates but tends to concentrate in spring in Mediterranean and subtropical cultivation. The fruits are small, green, three-lobed capsules typical of the genus.
Distribution and Habitat
Euphorbia ammak is endemic to the western Arabian Peninsula, with its native range restricted to western Saudi Arabia (principally the Hejaz and Asir regions) and northern Yemen. This distribution makes it the only large candelabra euphorbia native to the Arabian Peninsula — a biogeographically significant distinction, since all other arborescent candelabra species of comparable stature (Euphorbia ingens, Euphorbia candelabrum, Euphorbia abyssinica, Euphorbia cooperi) are restricted to mainland Africa.
The species inhabits rocky plains, precipitous hillsides, and thorny scrublands within the arid and semi-arid biome. It grows in wadis (seasonal watercourses) and on dry slopes at low to moderate elevations. While historically more widespread, Euphorbia ammak has become rare across much of its native range due to habitat degradation and overgrazing, though it reportedly remains locally common in parts of northern Yemen.
Conservation Status
Euphorbia ammak was assessed as Vulnerable (VU) on the IUCN Red List in 1998. The primary threats include habitat loss from agricultural expansion, urbanisation, and degradation of the arid scrubland ecosystems of the Hejaz and Yemeni highlands. The species’ restricted endemic range on the Arabian Peninsula amplifies its vulnerability; unlike continental African candelabra euphorbias that span multiple countries, the entire wild population of Euphorbia ammak is concentrated in two nations experiencing significant land-use change.
As a succulent Euphorbia, the species is listed under CITES Appendix II, which regulates international trade by requiring export permits. Artificially propagated specimens are widely available in the horticultural trade and do not contribute to wild collection pressure.
Euphol: A Triterpene with Anticancer Properties
One of the most scientifically significant aspects of Euphorbia ammak is the presence of euphol in its latex and leaf tissues. Euphol (C₃₀H₅₀O) is a tetracyclic triterpene alcohol classified within the Euphane subclass that occurs across many species in the Euphorbiaceae, most notably Euphorbia tirucalli.
A phytochemical study published in the Journal of Pharmacognosy and Phytotherapy (2014) investigated the chloroform extract of Euphorbia ammak leaves collected in Saudi Arabia and isolated three compounds: euphol, α-glutinol, and stigmasterol. All three showed cytotoxic activity in vitro against human cervical adenocarcinoma (HeLa) cells, with euphol demonstrating the strongest activity — an IC₅₀ of 9.25 μg/ml combined with a resistance fraction of only 13%. Thin layer chromatography confirmed that euphol was the predominant compound in the milky latex of the leaves.
This finding places Euphorbia ammak within a broader pharmacological context. Euphol has attracted substantial research attention across multiple cancer types: in vitro screening on 73 human cancer cell lines showed particular sensitivity in pancreatic and oesophageal carcinoma cells, with IC₅₀ values as low as 1.41 μM. The compound has demonstrated pro-apoptotic, anti-proliferative, anti-inflammatory, and anti-nociceptive properties, and has shown synergistic interactions with conventional chemotherapy agents such as gemcitabine and paclitaxel. More recently, a 2024 study explored Euphorbia ammak phytochemicals through structure-based drug discovery for breast and lung cancer biomarkers.
⚠ Critical safety disclaimer — the remedy is also a poison. Euphol research remains entirely at the in vitro and preclinical stage: no approved drug, supplement, or therapeutic protocol based on euphol currently exists for human use. The very same latex that contains this promising molecule is an extremely caustic and toxic substance. Direct contact with the milky sap of Euphorbia ammak causes severe chemical burns to the skin and mucous membranes, and can result in permanent eye damage including blindness if it reaches the eyes. Ingestion of any part of the plant or its latex can provoke intense inflammation of the digestive tract, vomiting, and systemic toxicity. Cases of severe poisoning from Euphorbia latex — including fatalities — are documented in the medical literature. Under no circumstances should the raw latex, leaves, stems, or any unprocessed part of Euphorbia ammak be consumed, applied topically, or used as a home remedy. The gap between a compound showing cytotoxic activity in a laboratory dish and a safe, effective medicine for human patients is vast, requiring years of pharmacological development, dosage calibration, toxicity testing, and clinical trials. Self-medication with Euphorbia latex in the hope of anticancer benefits is not only ineffective but genuinely life-threatening.
The Euphorbia ammak ‘Variegata’ Confusion
The cultivar Euphorbia ammak ‘Variegata’ is one of the most popular large succulent houseplants in the world — and one of the most frequently misidentified. Plants displaying a marbled pattern of creamy-yellow and pale blue-green are routinely sold under names including Euphorbia ingens ‘Variegata’, Euphorbia ingens ‘Marmorata’, Euphorbia abyssinica ‘Variegata’, and Euphorbia erythraeae f. variegata. In reality, the overwhelming majority of variegated large candelabra euphorbias in the commercial trade are Euphorbia ammak ‘Variegata’.
How to Distinguish Euphorbia ammak from Similar Species
The confusion is understandable, as several large candelabra euphorbias share a similar overall habit. However, a combination of morphological characters allows reliable identification:
Versus Euphorbia ingens (South and East Africa): The rib margins of Euphorbia ammak display a distinctly wavy, undulate pattern, while those of Euphorbia ingens tend to grow straight. The spine shields of Euphorbia ammak are obtriangular (elongated, inverted-triangular), whereas those of Euphorbia ingens are circular. Euphorbia ingens also develops far more branches at maturity, forming a dense, hemispherical crown that can resemble a Dracaena draco canopy, while Euphorbia ammak remains more open and loosely branched. No variegated form of the true Euphorbia ingens has been confirmed by Euphorbia specialists; virtually all plants sold as “variegated ingens” are Euphorbia ammak.
Versus Euphorbia abyssinica (Ethiopia, Eritrea, Sudan): Euphorbia abyssinica develops five to eight ribs at maturity versus the constant four of Euphorbia ammak. Its spines are more densely packed and more lethal-looking, and its branches are generally more upright and tightly clustered. True Euphorbia abyssinica is rarely encountered in commercial cultivation; most plants sold under this name are either Euphorbia ammak or other misidentified taxa.
Versus Euphorbia candelabrum (tropical East Africa): Euphorbia candelabrum is a much larger tree, reaching up to 20 metres, with a broader, more rounded crown. It also develops more ribs per branch than Euphorbia ammak.
Variegation in Euphorbia ammak
The variegation in Euphorbia ammak ‘Variegata’ is chimaeral, resulting from a somatic mutation that produces chlorophyll-deficient tissue alongside normal green tissue. This creates the distinctive marbling pattern. Because variegated tissue is less photosynthetically efficient, ‘Variegata’ specimens generally grow more slowly than the typical green form, produce smaller leaves, and may be somewhat less vigorous in sub-optimal conditions. The degree of variegation is variable: some plants are predominantly creamy-white with minimal green, while others are mostly green with sporadic lighter streaking.
Crested (cristata) forms of Euphorbia ammak also circulate in the trade, sometimes combined with the variegation to produce crested-variegated specimens that command premium prices among collectors.
Cultivation and Care
Euphorbia ammak is a rewarding plant for Mediterranean, subtropical, and arid-climate gardens, and also performs well as a large container specimen in bright indoor settings.
Light
Full sun is ideal. In the wild, Euphorbia ammak grows fully exposed on open hillsides and rocky plains. In cultivation, at least six to eight hours of direct sunlight per day produces the best growth and colouration. Young plants tolerate partial shade and can be grown indoors near a bright south-facing window, but etiolation will occur in insufficient light. The variegated cultivar is slightly more sensitive to intense midday sun and may show scorch marks in extreme heat, particularly if the plant is not acclimated.
Temperature and Cold Hardiness
Euphorbia ammak is frost-tender. It tolerates temperatures down to approximately −3 °C (25 °F) for brief periods, but any sustained exposure below freezing causes necrosis along the thin rib margins, permanently disfiguring affected branches. New growth must originate from undamaged tissue below the injury. In USDA hardiness 10a to 11b (marginal in zone 9b), the species can be grown outdoors year-round with appropriate winter protection. In cooler climates, it must be overwintered indoors or in a frost-free greenhouse.
The ideal temperature range for active growth is 16–30 °C. The plant enters dormancy during cool winter months and should be kept dry and protected from temperatures below 5 °C for prolonged periods.
Watering
Like most arborescent euphorbias, Euphorbia ammak stores water in its thick stems and tolerates drought. However, it does not handle extended dry periods as well as smaller, globular succulent species. During the active growing season (spring through autumn), water thoroughly whenever the soil has dried several centimetres below the surface — roughly every one to two weeks depending on temperature and pot size. In winter, reduce watering dramatically, allowing the substrate to dry almost completely between irrigations. Overwatering and waterlogged soil cause root rot and are the most common cause of death in cultivation.
Substrate
A sharply draining mineral mix is essential. A standard cactus and succulent potting blend amended with additional pumice, perlite, or coarse sand (roughly 50–60% mineral fraction) works well. Clay pot culture improves drainage and aeration. Euphorbia ammak is not particular about soil pH.
Fertilisation
Feed with a balanced, half-strength liquid fertiliser once monthly during the growing season. Avoid fertilising during winter dormancy.
Propagation
Euphorbia ammak is most commonly propagated by stem cuttings. Cut a branch segment, allow the cut surface to dry and callus over for one to two weeks in a shaded, well-ventilated location, then plant the calloused end in dry, well-draining substrate. Rooting hormone is beneficial but not strictly necessary. Water sparingly until roots are established. The species can also be grown from seed, though seed is rarely available, and germination is slow and unpredictable.
Safety warning: the white latex released when cutting the plant is highly caustic. Always wear gloves and protective eyewear. Rinse any skin contact with cold water immediately. The latex can cause severe burns to the eyes and mucous membranes.
Pests and Problems
Euphorbia ammak is generally pest-resistant. Mealybugs are the most common issue, followed by occasional scale insects. Root rot from overwatering is by far the greatest cultivation risk. In outdoor settings, strong winds can snap top-heavy branches — mature specimens that become tall and loosely branched may require staking or judicious pruning to prevent toppling.
Uses in Landscape Design
In frost-free climates, Euphorbia ammak makes a dramatic architectural specimen. Its candelabra silhouette provides strong vertical accent in xeriscape, rock, Mediterranean, and desert gardens. It pairs naturally with other large succulents — Aloe trees, Pachypodium, Dracaena draco, agaves, and columnar cacti — and can serve as a living barrier or hedge when planted in rows, a traditional use in parts of Yemen.
In southern California, Euphorbia ammak (especially the variegated cultivar) has become one of the two most commonly planted large euphorbias alongside Euphorbia ingens, thriving in the Mediterranean climate of coastal areas from San Diego to the Bay Area. In Australia, the species has adapted particularly well to coastal environments.
As a container plant, Euphorbia ammak is excellent for five to ten years, after which it may outgrow most pot sizes. Indoor specimens can reach the ceiling within a few years in optimal light.
Sources
- Schweinfurth, G.A. (1899). Bulletin de l’Herbier Boissier, 7 (appendix 2): 319. [Original species description]
- 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.
- Rahman, M.A. et al. (2002). Notes on succulent plant species of Saudi Arabia. Bangladesh Journal of Plant Taxonomy 9(1): 25–40.
- Al-Yahya, M.A. et al. (2015). Chemical constituents from the leaves of Euphorbia ammak growing in Saudi Arabia. Journal of Pharmacognosy and Phytotherapy 7(2): 14–17. [Euphol isolation and cytotoxicity data]
- Silva, V.A.O. et al. (2018). In vitro screening of cytotoxic activity of euphol from Euphorbia tirucalli on a large panel of human cancer-derived cell lines. Experimental and Therapeutic Medicine 16(2): 557–566.
- Wang, L. et al. (2013). Euphol arrests breast cancer cells at the G1 phase through the modulation of cyclin D1, p21 and p27 expression. Molecular Medicine Reports 8(4): 1279–1285.
- Lin, M.W. et al. (2012). Euphol from Euphorbia tirucalli selectively inhibits human gastric cancer cell growth through the induction of ERK1/2-mediated apoptosis. Food and Chemical Toxicology 50(12): 4333–4339.
- Yasukawa, K. et al. (2000). Inhibitory effect of euphol, a triterpene alcohol from the roots of Euphorbia kansui, on tumour promotion by 12-O-tetradecanoylphorbol-13-acetate in two-stage carcinogenesis in mouse skin. Journal of Pharmacy and Pharmacology 52(1): 119–124.
Authority Pages
- POWO — Plants of the World Online, Royal Botanic Gardens, Kew: Euphorbia ammak Schweinf.
- CITES — Convention on International Trade in Endangered Species: Euphorbia ammak — Appendix II (succulent Euphorbia spp.)
- IUCN Red List — International Union for Conservation of Nature: Euphorbia ammak — Vulnerable (VU), assessed 1998
- IPNI — International Plant Names Index: Euphorbia ammak Schweinf.
- GBIF — Global Biodiversity Information Facility: Euphorbia ammak Schweinf.
- WFO — World Flora Online: Euphorbia ammak Schweinf.
- Wikispecies: Euphorbia ammak