The Euphorbiaceae — the spurge family — are one of the great puzzles and glories of the plant world. This is the fifth-largest family of flowering plants, with approximately 6,700–7,500 species spread across 218–300 genera (depending on the classification followed), spanning every continent except Antarctica and every growth form from creeping desert annuals to towering rainforest trees. Among its members are some of the most economically important plants on Earth (rubber, cassava, castor oil), some of the most popular ornamentals (poinsettia, croton, pencil cactus), some of the most dangerous (the genus Euphorbia includes species whose latex can blind and kill), and some of the most bizarre — succulent trees that mimic cacti so convincingly that even experienced botanists are fooled at first glance.
For growers of succulent plants, the Euphorbiaceae are second only to the Cactaceae and the Crassulaceae in importance. The genus Euphorbia alone contains roughly 500 succulent species — more than any other single genus in any family — and they include some of the most sought-after collector plants in the world. But to understand the succulent euphorbias, it helps to understand the family they belong to: its structure, its chaotic taxonomic history, and the remarkable diversity of forms it has produced across five continents.
Classification — A Family Dismembered and Reassembled
Euphorbiaceae sensu lato: the traditional, sprawling family
For most of the 20th century, the Euphorbiaceae were defined very broadly — “Euphorbiaceae sensu lato” — as a massive family of roughly 300+ genera and 8,000 species, united by a suite of morphological characters including unisexual flowers, often a single ovule per locule, and frequently a milky latex. The most influential classification was that of Grady Webster (1975, 1994), who divided this enormous family into five subfamilies: Phyllanthoideae, Oldfieldioideae, Acalyphoideae, Crotonoideae, and Euphorbioideae.
The molecular revolution: five families from one
Molecular phylogenetic studies in the late 1990s and 2000s — particularly the landmark work of Kenneth Wurdack and collaborators — revealed that Euphorbiaceae sensu lato were not monophyletic: the five subfamilies did not all share a single common ancestor exclusive to the family. The Angiosperm Phylogeny Group (APG II, 2003; APG III, 2009; APG IV, 2016) resolved this by splitting the old, broad family into five separate families:
- Euphorbiaceae sensu stricto — the uniovulate subfamilies (Acalyphoideae, Crotonoideae, Euphorbioideae). This is the Euphorbiaceae as currently defined. ~218–300 genera, ~6,700 species.
- Phyllanthaceae — segregated from the former Phyllanthoideae. Includes Phyllanthus, Breynia, Sauropus. ~59 genera, ~2,000 species.
- Picrodendraceae — segregated from the former Oldfieldioideae. ~24 genera, ~80 species.
- Putranjivaceae — segregated from Phyllanthoideae–Drypeteae. 3 genera, ~210 species.
- Pandaceae — segregated from Acalyphoideae–Galearieae. 3 genera, ~18 species.
This means that many plants once called “Euphorbiaceae” in older literature no longer belong to the family. The phyllanthus you see in a tropical garden or the drypetes in a botanical collection are now Phyllanthaceae and Putranjivaceae, respectively — not Euphorbiaceae. This matters for succulentes.net because the succulent genera — Euphorbia, Jatropha, Monadenium (now absorbed into Euphorbia) — all remain firmly within Euphorbiaceae sensu stricto.
Rafflesiaceae: the family within a family
One of the most extraordinary discoveries of the molecular era is that the Rafflesiaceae — the parasitic family that includes the largest flower in the world, Rafflesia arnoldii — are derived from within the Euphorbiaceae. Molecular evidence places them as highly modified, parasitic descendants of a euphorbiaceous ancestor, deeply nested within the family’s phylogeny. This is a stunning example of how extreme parasitism can obliterate all morphological resemblance to a plant’s true relatives.
The Three Subfamilies of Euphorbiaceae Sensu Stricto
Subfamily Euphorbioideae — the latex-bearing spurges
This is the largest and most horticulturally important subfamily, and the one that concerns succulent growers most directly. It is characterised by a toxic, milky latex — the defining feature that links the poinsettia to the pencil cactus and the candelabra tree. The latex contains diterpene esters (including phorbol esters and ingenol esters) that cause severe skin irritation, eye damage, and gastrointestinal toxicity. All members of this subfamily should be handled with gloves.
Principal genera of interest:
- Euphorbia L. — the giant of the family. Approximately 2,000 species, making it the second-largest genus of flowering plants after Astragalus. Found worldwide, but with centres of diversity in Africa, Madagascar, and the Americas. Includes roughly 500 succulent species ranging from globular “living stones” to 20-metre candelabra trees. The genus also includes non-succulent species like poinsettia (E. pulcherrima), leafy spurge (E. esula), and the Mediterranean shrub E. characias. The genus has absorbed several former genera: Monadenium, Synadenium, Pedilanthus, and Endadenium — all now placed within Euphorbia based on molecular evidence. Treated in our dedicated genus hub.
- Hura L. — the sandbox tree (Hura crepitans). A large tropical American tree whose trunk is covered in conical spines and whose ripe seed capsules explode with a loud crack, launching seeds at speeds up to 70 m/s. The latex is used as an arrow poison by indigenous peoples.
- Hippomane L. — the manchineel (Hippomane mancinella), often called the most dangerous tree in the world. Every part is toxic; standing beneath it in rain can cause skin blisters from latex-contaminated runoff.
- Excoecaria L. — the blind-your-eye mangrove (Excoecaria agallocha), whose latex causes temporary blindness on eye contact.
- Hevea Aubl. — the Pará rubber tree (Hevea brasiliensis). Although it belongs to Crotonoideae in some classifications, it is often discussed alongside Euphorbioideae because of its latex — but note that Hevea latex is innocuous, not toxic.
Subfamily Crotonoideae — the crotons and their allies
A large, predominantly tropical subfamily characterised by latex that is generally innocuous (not toxic like the Euphorbioideae latex). Pollen morphology and wood anatomy are key diagnostic features.
Principal genera of interest:
- Croton L. — approximately 1,200 species, the second-largest genus in the family. Mostly shrubs and small trees, pantropical. Croton lechleri produces “dragon’s blood” resin used in traditional medicine. Not to be confused with the ornamental “crotons” of the houseplant trade, which are Codiaeum variegatum (Crotonoideae as well, but a different genus).
- Codiaeum A.Juss. — the garden croton (Codiaeum variegatum). One of the most popular tropical foliage houseplants, with hundreds of cultivars in every colour from green to yellow, orange, red, and near-black. Native to Indonesia and Malaysia.
- Jatropha L. — approximately 170 species, pantropical. Includes succulent caudiciform species highly prized by collectors (Jatropha podagrica, the “Buddha belly plant”; Jatropha cathartica) as well as the biofuel crop Jatropha curcas (Barbados nut). The genus produces a clear to slightly milky sap, not the white latex of Euphorbia.
- Hevea Aubl. — ~10 species, South American. Hevea brasiliensis is the primary source of commercial natural rubber — one of the most economically important plants on Earth.
- Manihot Mill. — approximately 100 species, American. Manihot esculenta (cassava, manioc) is the third-largest source of carbohydrate calories in the tropics, feeding over half a billion people daily. The roots contain cyanogenic glycosides that must be processed before consumption.
- Ricinus L. — a monotypic genus. Ricinus communis, the castor oil plant, is the source of castor oil (used industrially and medicinally) and of ricin — one of the most potent biological toxins known, classified as a biological weapon. A single seed can kill an adult if ingested.
Subfamily Acalyphoideae — the copperleaves
The third subfamily, characterised by the absence of milky latex (the sap is clear or coloured but not milky) and by diverse floral morphology. Many members have stinging hairs.
Principal genera of interest:
- Acalypha L. — approximately 500 species, the third-largest genus in the family. Pantropical herbs, shrubs, and small trees. The ornamental Acalypha hispida (chenille plant, “red-hot cat-tail”) and Acalypha wilkesiana (copperleaf) are widely cultivated.
- Macaranga Thouars — approximately 300 species, Old World tropics. Pioneer trees of forest gaps, often with spectacular peltate leaves. Several species have mutualistic relationships with ants.
- Tragia Plum. ex L. — approximately 150 species, pantropical. Characterised by abundant stinging hairs.
- Dalechampia Plum. ex L. — approximately 130 species, pantropical vines with elaborate floral bracts that attract resin-collecting bees.
Diversity of Forms
The Euphorbiaceae display an almost unparalleled range of growth forms for a single family:
Succulent trees and shrubs. The candelabra euphorbias of Africa (Euphorbia ingens, Euphorbia ammak, Euphorbia candelabrum) converge so completely with the columnar cacti of the Americas that they are routinely mistaken for cacti. This is the textbook example of convergent evolution: two unrelated lineages on two continents evolving identical solutions to the same arid environment.
Succulent globulars. Euphorbia obesa, Euphorbia meloformis, and Euphorbia symmetrica form spherical to cylindrical bodies that mimic Astrophytum and Ferocactus cacti — complete with ribs and a superficially similar surface texture.
Medusoid euphorbias. Euphorbia caput-medusae, Euphorbia flanaganii, and relatives produce a central caudex from which numerous snake-like succulent arms radiate — the “Medusa’s head” form, unique to the Euphorbiaceae.
Caudiciform succulents. Euphorbia stellata, Euphorbia cylindrifolia, Jatropha podagrica, and many Malagasy species produce a swollen, woody caudex with seasonal deciduous branches — prized by collectors for their sculptural, bonsai-like appearance.
Tropical timber trees. Hevea brasiliensis (rubber), Hura crepitans (sandbox tree), and many Macaranga species are large rainforest trees with no hint of succulence.
Herbaceous weeds and annuals. Euphorbia peplus (petty spurge), Euphorbia helioscopia (sun spurge), and Chamaesyce species (now included in Euphorbia) are small annual weeds of disturbed ground worldwide.
Subshrubs and perennial border plants. Euphorbia characias, Euphorbia myrsinites, Euphorbia rigida, and Euphorbia polychroma are frost-hardy Mediterranean and European species widely used in temperate ornamental gardens — completely different in ecology and appearance from their succulent African relatives.
Geophytes with underground storage. Several Malagasy euphorbias and some African species produce tuberous or rhizomatous underground organs that survive the dry season, sending up annual above-ground shoots.
Parasitic plants. The Rafflesiaceae, derived from within the Euphorbiaceae, have abandoned photosynthesis entirely and parasitise the roots of tropical vines.
The Latex — Chemistry, Danger, and Function
The milky latex of the Euphorbioideae is the family’s most notorious and ecologically important feature. It is produced in specialised laticifer cells that form a network throughout the plant body, under pressure, so that any wound immediately releases a flow of white sap.
The latex contains a complex cocktail of diterpene esters (phorbol esters, ingenol esters, resiniferatoxin in some species), triterpenes, and other secondary metabolites. These compounds cause severe contact dermatitis on skin, keratitis and potential blindness on eye contact, and gastrointestinal haemorrhage if ingested. Some species are co-carcinogenic (they promote tumour development in conjunction with other carcinogens) — notably Euphorbia tirucalli, which has been epidemiologically linked to Burkitt’s lymphoma in Africa.
The ecological function of the latex is primarily anti-herbivore defence. The diterpene esters are intensely unpalatable and toxic to most mammals, insects, and fungi, providing the plant with a highly effective chemical shield. This defence system has allowed succulent euphorbias to thrive in environments where cacti — which lack such potent chemical defences — rely instead on mechanical defence (spines).
Economic Importance
The Euphorbiaceae include plants of enormous economic significance:
Hevea brasiliensis — natural rubber. The global natural rubber industry (over 14 million tonnes annually) depends almost entirely on this single species.
Manihot esculenta — cassava. A staple food for over 500 million people in tropical regions, and the third-largest source of carbohydrate calories after rice and maize.
Ricinus communis — castor oil (industrial lubricant, pharmaceutical base) and ricin (biological toxin).
Jatropha curcas — biofuel crop, though commercial viability has been disappointing relative to early expectations.
Euphorbia pulcherrima — poinsettia. One of the most commercially successful ornamental plants in the world, with over 70 million plants sold annually in the United States alone.
Codiaeum variegatum — garden croton. A major tropical foliage houseplant with hundreds of cultivars.
Genera of Interest for Succulent Growers
For the audience of succulentes.net, the following genera within the Euphorbiaceae are the most relevant:
Euphorbia — the dominant genus, with ~500 succulent species. Treated in our dedicated genus hub.
Jatropha — caudiciform succulents, particularly Jatropha podagrica (Buddha belly), Jatropha cathartica, Jatropha multifida (coral plant).
Synadenium (now included in Euphorbia) — the former Synadenium grantii (now Euphorbia umbellata) is a popular succulent houseplant.
Monadenium (now included in Euphorbia) — succulent East African species, formerly a separate genus, now absorbed into Euphorbia. Monadenium ritchiei (now Euphorbia ritchiei) is widely grown.
Pedilanthus (now included in Euphorbia) — the slipper spurges, characterised by zygomorphic (bilaterally symmetrical) cyathia. Pedilanthus tithymaloides (now Euphorbia tithymaloides) is a common tropical garden plant.
Sources and Further Reading
- Plants of the World Online (POWO), Royal Botanic Gardens, Kew — Euphorbiaceae. powo.science.kew.org
- Wurdack, K.J., Hoffmann, P. & Chase, M.W. (2005). Molecular phylogenetic analysis of uniovulate Euphorbiaceae (Euphorbiaceae sensu stricto) using plastid rbcL and trnL-F DNA sequences. American Journal of Botany, 92(8): 1397–1420.
- Webster, G.L. (1994). Classification of the Euphorbiaceae. Annals of the Missouri Botanical Garden, 81: 3–32.
- Radcliffe-Smith, A. (2001). Genera Euphorbiacearum. Royal Botanic Gardens, Kew.
- Horn, J.W., van Ee, B.W., Morawetz, J.J., Riina, R., Steinmann, V.W., Berry, P.E. & Wurdack, K.J. (2012). Phylogenetics and the evolution of major structural characters in the giant genus Euphorbia L. Molecular Phylogenetics and Evolution, 63(2): 305–326.
- Carter, S. & Leach, L.C. (2001). Euphorbiaceae. Flora Zambesiaca, 9(5).
- Govaerts, R., Frodin, D.G. & Radcliffe-Smith, A. (2000). World Checklist and Bibliography of Euphorbiaceae (with Pandaceae). Royal Botanic Gardens, Kew.
- APG IV (2016). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants. Botanical Journal of the Linnean Society, 181: 1–20.