Euphorbia didiereoides Denis ex Leandri (1934) is an endangered, spiny succulent shrub from southern Madagascar whose very name reveals its most remarkable feature: it so closely resembles species of Alluaudia (Didiereaceae) that the botanists who described it named it “the one that looks like Didierea.” This morphological convergence between two unrelated plant families — Euphorbia (Euphorbiaceae) and the endemic Malagasy Didiereaceae — growing side by side in the same arid habitat, represents one of the most striking examples of convergent evolution among succulent plants. Known from only six localities and three subpopulations in southern Madagascar, Euphorbia didiereoides is assessed as Endangered (EN) on the IUCN Red List and has been flagged by CITES for significant trade review due to ongoing collection pressure on wild populations.
Taxonomy and Nomenclature
Euphorbia didiereoides was described by the French botanist Marcel Denis and published by Jacques Leandri in 1934, in the Bulletin du Muséum National d’Histoire Naturelle (series 2, volume 6, page 121). The specific epithet didiereoides is constructed from Didierea (a genus of spiny trees in the Didiereaceae, endemic to Madagascar) and the Greek suffix -oides (“resembling”), directly referencing the plant’s extraordinary resemblance to members of that unrelated family, particularly the genus Alluaudia.
Within the genus Euphorbia, the species is classified in subgenus Euphorbia, section Goniostema — the same section that includes Euphorbia milii (the crown of thorns) and its relatives. This placement within the thorny Malagasy euphorbia radiation, rather than among the African candelabra species of section Euphorbia, underscores the independent evolutionary origin of the candelabra-like and spiny shrub forms on Madagascar.
According to Plants of the World Online (POWO, Kew), Euphorbia didiereoides has no accepted synonyms — an unusually clean nomenclatural record. The native range is given as southern Madagascar.
Common names: Madagascar spiny euphorbia. No widely established vernacular name exists in English, reflecting the species’ rarity in cultivation.
Convergent Evolution: When an Euphorbia Becomes an Alluaudia
The most compelling botanical story of Euphorbia didiereoides is its convergent resemblance to species of Alluaudia — a genus of spiny, succulent trees in the Didiereaceae (now placed in subfamily Didiereoideae within Cactaceae by some molecular phylogenies, or maintained as a distinct family by others). The Didiereaceae are among the most iconic endemic plant families of Madagascar, forming the dominant structural component of the island’s extraordinary spiny forests in the southwest.
Euphorbia didiereoides and Alluaudia species share a remarkably similar general architecture: erect, densely spiny, columnar stems bearing small, deciduous leaves during the rainy season, the whole plant forming a V-shaped or conical outline. The spines are thick, numerous, irregularly arranged, and of variable size (5–25 mm). The deciduous leaves are green, pubescent, elliptical with a mucronate (short-pointed) apex, lacking a petiole but with a prominent white midrib. In the field, a casual observer could easily mistake Euphorbia didiereoides for a small Alluaudia.
Yet these two plant lineages are separated by vast evolutionary distance. The Didiereaceae belong to the order Caryophyllales (alongside cacti, portulacas, and carnations), while Euphorbia belongs to the order Malpighiales. Their morphological convergence evolved independently under the selective pressures of the same harsh, arid Malagasy environment — intense drought, nutrient-poor substrates, and pressure from browsing herbivores (historically including giant tortoises and lemurs).
This is one of the most elegant examples of convergent evolution in the plant kingdom: two unrelated lineages, in the same habitat, evolving nearly identical vegetative forms while maintaining fundamentally different reproductive structures (cyathia in Euphorbia, conventional flowers in Alluaudia).
Description and Morphology
Euphorbia didiereoides is a semi-succulent, spiny, erect shrub or small tree reaching 2 to 4 metres tall in adult specimens (some sources report up to 2.5 m, but field observations by Castillon & Rajaovelona indicate 2–4 m for mature individuals). The growth habit is typically a single main stem or two to three stems branching from the base, developing numerous lateral ramifications that give the plant the overall shape of an inverted cone.
Stems
The main stem can reach up to 15 cm in diameter near the base, tapering progressively to approximately 3 cm at the apex. The stems are grey-green, densely covered with stout spines. Short lateral branches (brachyblasts) are produced, reaching up to approximately 2 cm long, though these are relatively rare; the stems are instead covered with small protuberances from which spines and leaves emerge.
Spines
The spines are one of the most distinctive features: thick, grey with reddish tips, densely arranged without any regular alignment, rarely solitary, and variable in size from 5 to 25 mm. This irregular, dense spine coverage contributes heavily to the Alluaudia-like appearance.
Leaves
The leaves are deciduous, appearing during the growing season (rainy period) and falling during drought. They are elliptical, green, pubescent (finely hairy), with a mucronate apex, sessile (without petiole), and bear a conspicuous white midrib. A slight red tinge is often visible, adding subtle colour to the foliage. The leaves are small relative to the plant’s size, consistent with a drought-adapted xerophytic strategy.
Flowers
The inflorescences are capitate (head-shaped) incyathescences — dense clusters of cyathia on peduncles up to 8 cm long, containing up to 64 individual cyathia per cluster. The flowers are small and green, with coloured cyathophylls (bracts) typical of section Goniostema. The peduncle is pubescent. The fruits are pubescent capsules.
Distribution and Habitat
Euphorbia didiereoides is endemic to southern Madagascar, where it inhabits the arid and semi-arid desert and dry shrubland biome. The species is restricted to rocky areas within the spiny forest ecosystem — one of the most biologically unique and threatened habitats on Earth. The Madagascar spiny forests harbour 48% endemic genera and 95% endemic species at the plant level, making them one of the Global 200 priority ecoregions for conservation.
According to the CITES Review of Significant Trade, Euphorbia didiereoides is known from only six localities and three subpopulations within a single area of southern Madagascar. This extremely restricted distribution, combined with the ongoing degradation of the spiny forest ecosystem, places the species in a precarious conservation position.
Conservation Status: Endangered and Under Trade Pressure
Euphorbia didiereoides was assessed as Endangered (EN) on the IUCN Red List in 2004 (assessment by Haevermans). The principal threats are:
Habitat degradation and fire. The Madagascar spiny forests are among the most threatened ecosystems on the island. Slash-and-burn agriculture (tavy), charcoal production, overgrazing by goats and cattle, and uncontrolled fires are progressively reducing and fragmenting the habitat. Southern Madagascar has experienced severe droughts in recent decades, compounding the stress on already fragile plant communities.
Collection for horticulture. Despite its Endangered status, Euphorbia didiereoides is collected from wild populations for the specialist succulent trade. CITES records show that Madagascar reported exports of 35 wild-collected live specimens between 1999 and 2008. While these numbers appear small, they are significant for a species known from only six localities. The CITES Plants Committee selected Euphorbia didiereoides for its Review of Significant Trade (PC19, 2010), flagging concerns about whether Madagascar was making adequate non-detriment findings before authorising exports.
Limited protected area coverage. Although the species is known from two areas that potentially qualify as protected under Madagascar’s New System of Conservation Areas, the actual level of protection afforded is uncertain.
Under CITES, Euphorbia didiereoides is listed in Appendix II as part of the succulent Euphorbia genus listing. It does not benefit from any of the cultivar exemptions applied to Euphorbia trigona, Euphorbia lactea, or Euphorbia milii.
Euphorbia pseudodidiereoides: A Critically Endangered Sister Species
In 2019, Castillon and Rajaovelona described a new species, Euphorbia pseudodidiereoides, from an isolated quartzite massif in the Ihorombe region of south-central Madagascar. This species is the presumed closest relative of Euphorbia didiereoides, sharing the Alluaudia-like habit, dense spination, pubescent leaves, and capitate inflorescences. It differs in its smaller stature (0.8–1.5 m versus 2–4 m), recumbent (drooping) terminal branches, and shorter, less dense incyathescences with broader, more rounded cyathophylls.
Euphorbia pseudodidiereoides is assessed as Critically Endangered (CR), known from a single locality. Its discovery underscores both the extraordinary endemism of the Malagasy euphorbia flora and the urgency of botanical exploration and conservation in the rapidly vanishing dry habitats of southern Madagascar.
Cultivation and Care
Euphorbia didiereoides is rare in cultivation and grown primarily by specialist collectors of Malagasy succulents. It is offered by a handful of specialist nurseries (such as Red Island Plants) that propagate the species from cultivated stock.
Light
Full sun is essential. In its native habitat, Euphorbia didiereoides grows fully exposed on rocky, open slopes in one of the most intensely sunlit environments on Earth. In cultivation, provide the maximum available sunlight — a south-facing position under glass, or direct outdoor sun in frost-free climates.
Temperature and Cold Hardiness
Euphorbia didiereoides is strictly tropical with no frost tolerance. It is rated for USDA hardiness zones 10b to 11b (minimum approximately +1.7 °C / 35 °F). In practice, temperatures below 10 °C should be avoided for extended periods, and any frost exposure is likely fatal. In all non-tropical climates, the species must be grown in a heated greenhouse or as a carefully managed indoor specimen.
Watering
Water sparingly during the growing season, allowing the substrate to dry completely between irrigations. During the cool/dry season, keep the plant almost completely dry. The species is adapted to the highly seasonal rainfall regime of southern Madagascar, where prolonged drought is normal. Overwatering, particularly during dormancy, causes root rot — the primary cause of death in cultivation.
Substrate
A very sharply draining mineral mix is essential — more mineral-heavy than a standard cactus blend. A mix of 60–70% pumice, perlite, or coarse volcanic gravel with 30–40% composted organic matter works well. Excellent drainage is non-negotiable.
Propagation
Propagation is by stem cuttings or, rarely, from seed. Cuttings should be taken during the active growing season, calloused for one to two weeks, and planted in dry mineral substrate. Rooting is slow and success rates are lower than for more vigorous euphorbia species. Seed, when available, germinates slowly and unpredictably.
Growth Rate
Slow. Euphorbia didiereoides is not a fast grower in cultivation, and patience is required. Specimens take many years to develop the characteristic dense spination and branching pattern seen in mature wild plants.
Sources
- Denis, M. (1934). Bulletin du Muséum National d’Histoire Naturelle, sér. 2, 6: 121. [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.
- Haevermans, T. (2004). Euphorbia didiereoides. The IUCN Red List of Threatened Species 2004: e.T44335A10893121.
- Rebmann, N. (2007). Les Euphorbes de Madagascar. Succulentes Spécial: 1–48.
- Castillon, J.-P. & Rajaovelona, L.R. (2019). Euphorbia pseudodidiereoides, une nouvelle euphorbe épineuse du Centre-sud de Madagascar. Malagasy Nature 13: 60–64.
- Aubriot, X., Lowry, P.P. II & Haevermans, T. (2021). Taxonomic changes and new species in Malagasy Euphorbia (Euphorbiaceae). Phytotaxa 492(1): 1–55.
- CITES Plants Committee (2010). Review of Significant Trade: Euphorbia spp. PC19 Doc. 12.3, Annex 3.
Authority Pages
- POWO — Plants of the World Online, Royal Botanic Gardens, Kew: Euphorbia didiereoides Denis ex Leandri
- IUCN Red List — International Union for Conservation of Nature: Euphorbia didiereoides — Endangered (EN), assessed 2004
- CITES — Convention on International Trade in Endangered Species: Euphorbia didiereoides — Appendix II, selected for Review of Significant Trade (PC19, 2010)
- GBIF — Global Biodiversity Information Facility: Euphorbia didiereoides
- iNaturalist: Euphorbia didiereoides
- Wikispecies: Euphorbia didiereoides