Euphorbia polygona

Euphorbia polygona
Growing from beside a boulder, south of Makhanda, South Africa
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Embryophytes
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Malpighiales
Family: Euphorbiaceae
Genus: Euphorbia
Species:
E. polygona
Binomial name
Euphorbia polygona
Synonyms[1]
  • Euphorbia anoplia
  • Euphorbia cucumerina
  • Euphorbia horrida
  • Euphorbia polygonata

Euphorbia polygona, the many-angled cactus euphorbia, is a plant in the spurge family native to dry areas of South Africa.

Description

Euphorbia polygona is a hairless succulent with many stems that can be 15 centimeters to 2 meters in length.[2] The overall appearance is very similar to columnar cactuses from the Americas.[3] Stems branch near the base of the plant, very rarely further up, and grow a fibrous root network from the base of the main stem or some of the branches. On occasion plants will produce short rhizomes, 2–10 cm long. The stems tend to be club-shaped, larger in diameter towards the top than at the base, with a width of 4–30 cm, though usually not more than 20 cm.[2]

The stems are covered in tubercles, cone shaped outgrowths, they fuse to make seven to twenty ribs on the stems.[4] They are often quite narrow and wavy.[5] The groves between the ribs can be as much as 1.5 cm deep;[6] they can go straight up the stems or less frequently twist around them.[3] Towards the top of the stems small 1–2 mm long and 1 mm wide vestigial leaves are produced, but are not retained for long.[2]

The thorns on the ribs are long lasting peduncles, the stalks that attach to the flowers,[7] 0.4–4 cm long and 1–3 mm thick at the base.[2] Some of these peduncles are modified to never produce flowers and on other plants they are absent.[2] Usually the spines are in groups of two to five.[8] The flowers are produced near the top of the stems, but not at its very end, in the joints between the tubercles atop the ribs.[2]

Taxonomy

Euphorbia polygona was given its scientific name in 1803 by Adrian Hardy Haworth. It is part of genus Euphorbia which is classified in the Euphorbiaceae family.[1] According to Plants of the World Online it has no accepted varieties,[1] but due to many botanists reducing Euphorbia horrida to a synonym of E. polygona the botanist Detlef H. Schnabel has argued for the recognition of a variety named horrida to prevent the loss of genetic diversity in the species.[9]

If Euphorbia horrida is considered to be a synonym, then Euphorbia polygona has 18 heterotypic synonyms including 4 species and 14 varieties.[1]

Table of Synonyms
Name Year Rank Notes
Euphorbia anoplia Stapf 1923 species
Euphorbia cucumerina Willd. 1799 species
Euphorbia horrida Boiss. 1860 species
Euphorbia horrida var. major A.C.White, R.A.Dyer & B.Sloane 1941 variety
Euphorbia horrida var. noorsveldensis A.C.White, R.A.Dyer & B.Sloane 1941 variety
Euphorbia horrida var. striata A.C.White, R.A.Dyer & B.Sloane 1941 variety
Euphorbia polygona var. alba D.H.Schnabel 2014 variety
Euphorbia polygona var. ambigua D.H.Schnabel 2014 variety
Euphorbia polygona var. anoplia (Stapf) D.H.Schnabel 2013 variety
Euphorbia polygona var. exilis D.H.Schnabel 2012 variety
Euphorbia polygona var. hebdomadalis D.H.Schnabel 2012 variety
Euphorbia polygona var. horrida (Boiss.) D.H.Schnabel 2014 variety
Euphorbia polygona var. major (A.C.White, R.A.Dyer & B.Sloane) D.H.Schnabel 2013 variety
Euphorbia polygona var. minor D.H.Schnabel 2013 variety
Euphorbia polygona var. nivea D.H.Schnabel 2011 variety
Euphorbia polygona var. noorsveldensis (A.C.White, R.A.Dyer & B.Sloane) D.H.Schnabel 2013 variety
Euphorbia polygona var. striata (A.C.White, R.A.Dyer & B.Sloane) D.H.Schnabel 2013 variety
Euphorbia polygonata G.Lodd. 1828 species nom. subnud.

Names

Euphorbia polygona is known by the common name many-angled cactus euphorbia.[10] The name African milk barrel, a name previously used for E. horrida, is now applied to the species by writers who accept the merger of the two taxa.[11] It has also been called baboon's noors, from an Afrikaans name for the plant, baviaansnoors.[12]

Range and habitat

Euphorbia polygona is endemic to the country of South Africa where it is found in the Western and Eastern Cape provinces.[13] There is grows from areas near Uniondale in the eastern part of the Western Cape in the Kouga, Baviaanskloof, Groot Winterhoek, and Suurberg mountains to the area near Makhanda in the Eastern Cape.[5]

In the Cape Fold Belt it often is found on drier, rocky sandstone outcrops in relatively wet areas, often on the hotter north or east facing slopes. To the north on the edge of the Great Karoo it grows in flatter areas and hills, often on shale.[5]

Ecology

The cactus euphorbias, regardless of if E. horrida and E. polygona, have long been recognized as the only natural host for the mistletoe Viscum minimum. It grows within the stems of the plants pushing out small leaves and flowering shoots.[6] In cultivation the related Euphorbia stellispina has been found to be a suitable host for the parasite.[14] Plants shorter than 15 cm are considerably weakened by the parasite causing some tissue death and possibly killing the host.[15]

Cultivation

Many-angled cactus euphorbia has a long history of cultivation outside its native habitat, with the first records of it being grown in Europe dating from 1790.[10] They are also grown in Karoo gardens and containers in their native South Africa.[16]

Succulent euphorbias are readily propagated in cultivation from cuttings that are allowed to heal for 14 days before being planted into moist sand to root. Plants are also grown from seed planted in well drained soil with germination occurring after three to four weeks in warm conditions.[16]

The plant is mildly poisonous to humans. The milky sap can cause mild to severe skin irritation and itching or permanent damage to the eyes.[11]

The cultivar 'Snowflake' is valued by plant growers for the exceptionally generous coating of natural waxes giving its cactus-like stems a whitened appearance.[17] It entered the plant trade in the 1980s and was variously labeled as E. horrida and E. polygona prior to their merger.[18]

References

Citations

  1. 1 2 3 4 POWO 2026.
  2. 1 2 3 4 5 6 Bruyns 2022, p. 157.
  3. 1 2 Scott 1958, p. 141.
  4. ↑ Bruyns 2022, pp. 157–158.
  5. 1 2 3 Bruyns 2022, p. 158.
  6. 1 2 Rauh 1984, p. 49.
  7. ↑ Bruyns 2012, p. 517.
  8. ↑ WFO 2026.
  9. ↑ Schnabel 2013, pp. 6–7.
  10. 1 2 Smith & Van Wyk 2008, p. 174.
  11. 1 2 NC State Extension n.d.
  12. ↑ White, Dyer & Sloane 1941, p. 843.
  13. ↑ Hassler 2026.
  14. ↑ Horwood 1983, p. 46.
  15. ↑ Horwood 1983, p. 467.
  16. 1 2 Powrie 1998, p. 297.
  17. ↑ Trager 1987, p. 26.
  18. ↑ Kemble 2021.

Sources

Books

  • Bruyns, Peter V. (2022). Euphorbia in Southern Africa. Vol. 1 (1st ed.). Cham: Springer International Publishing AG. doi:10.1007/978-3-030-49402-5. ISBN 978-3-030-49402-5. OCLC 1337156939.
  • Bruyns, P.V. (2012). "Euphorbia". In Manning, John; Goldblatt, Peter (eds.). Plants of the Greater Cape Floristic Region. Vol. 1: The Core Cape Flora. Pretoria, South Africa: SANBI, Biodiversity for Life. pp. 513–518. ISBN 978-1-919976-74-7. OCLC 866860203. Retrieved 18 May 2026.
  • Powrie, Fiona (1998). Grow South African plants : a gardeners' companion to indigenous plants. Claremont, South Africa: National Botanical Institute, Kirstenbosch. ISBN 978-1-919684-15-4. OCLC 43263113. Retrieved 18 May 2026.
  • Rauh, Werner (1984). The Wonderful World of Succulents: Cultivation and Description of Selected Succulent Plants Other than Cacti (Second, Revised ed.). Washington, D.C.: Smithsonian Institution Press. ISBN 978-0-87474-780-5. OCLC 10072928. Retrieved 18 May 2026.
  • Scott, S. H. (1958). The Observer's Book of Cacti and Other Succulent. London: Frederick Warne & Co. OCLC 311289. Retrieved 18 May 2026.
  • Smith, Gideon; Van Wyk, Ben-Erik (2008). The Garden Succulents Primer. Portland, Oregon: Timber Press. ISBN 978-0-88192-954-6. OCLC 226356849. Retrieved 18 May 2026.
  • White, Alain; Dyer, R. Allen; Sloane, Boyd L. (1941). The Succulent Euphorbieae (Southern Africa). Vol. II. Pasadena, California: Abbey Garden Press. OCLC 1820590. Retrieved 18 May 2026.

Journal articles

Web sources

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