PlantLife Volume 58.5, December 2024. South Africa's Succulent Euphorbias

 

South Africa's Succulent Euphorbias

 

Text and photographs by Detlef H. Schnabel

 

Introduction

Euphorbia, commonly known as spurge, is a cosmopolitan genus within the family Euphorbiaceae and is found across all climatic regions worldwide, except for subpolar and polar zones. It is one of the largest and most diverse genera of flowering plants, comprising over 2,000 recognised species (Radcliffe-Smith, 2001). 

The genus  Euphorbia was named by the Swedish biologist and physician Carl Linnaeus in honour of Euphorbus, a physician who served King Juba II of Numidia and Mauretania (52–50 BC – 23 AD). The common name 'spurge', applied to euphorbias, derives from the French word espurgier, meaning 'to purge', reflecting the purported purgative properties of the latex found in Euphorbia when consumed. Euphorbias have been used medicinally since ancient times.

While most species of Euphorbia are generally non-succulent, typically comprising herbaceous perennials and shrubs, Bruyns (2022) notes that the majority (79%) of the 172 species native to southern Africa (specifically Namibia and South Africa) are succulent—a term derived from the Latin word ‘succulentus‘ meaning 'juicy' or 'full of sap'. These species exhibit thickened, fleshy structures, such as stems, which are adapted for water storage, thereby enabling them to endure prolonged periods of drought without sustaining damage.

What makes a Euphorbia?

A key taxonomic feature of Euphorbia species—with a few exceptions—is their white, milky, and bitter-tasting sap or latex, which serves to protect them against herbivory. 

Whether Euphorbia sap is toxic or not is a subject of ongoing debate. Some prominent South African botanists assert that euphorbias are not poisonous (P.V. Bruyns and E. Van Jaarsveld, personal communications, 20 September 2024). Although the sap may not be toxic or poisonous, it is well documented that contact with it can cause skin and eye irritation. Therefore, caution should always be exercised when handling these plants.

Milky latex  is also observed in some genera within other plant families, such as Asclepias and Cynanchum (commonly referred to as milkweeds) in the Apocynaceae (dogbane family), and therefore does not serve as a definitive distinguishing feature. In contrast, what uniquely distinguishes euphorbias from all other plants is their distinctive floral structure, known as the cyathium (plural: cyathia), that is found nowhere else in the plant kingdom. This complex, specialised inflorescence mimics a single flower but is, in fact, a cluster of highly reduced individual unisexual flowers (either male or female). The structure of this 'false flower' exemplifies an efficient reproductive strategy, frequently (though not invariably) grouping the staminate and pistillate flowers together in a compact unit, thereby facilitating more effective pollination. In this instance, it is a so-called bisexual or hermaphroditic cyathium. Its main components are:

 

Figure 1. The Cyathium:  The primary characteristics of a bisexual cyathium, as exemplified by Euphorbia procumbens, include: a) Nectar secreting glands,  b) A centrally located female flower, c) Encircling male flowers, d) the involucrum 

•    Central female flower: At the centre of the cyathium is a single female flower, reduced to a pistil containing a three-chambered ovary and devoid of both petals and sepals (leaf-like structures present in many 'true flowers').

 

•    Surrounding male flowers: Encircling the centrally positioned female flower are several reduced male flowers, each consisting of a single pollen-producing stamen and also lacking both petals and sepals.

 

•    Involucre: A specialised structure, cup- or bowl-shaped, composed of fused modified leaves known as bracts (referred to as the 'floral envelope'), which surrounds and supports the flowers.

 

•    Nectar glands: The cyathium typically contains nectar-secreting glands that emit a sweet, foetid, or indefinable scent. These glands are positioned on the rim of the involucre, attracting insects for pollination. They may vary in colour and size, thereby enhancing their appeal to pollinators. Often, the glands exhibit appendages of varying shapes and sizes, further increasing their visibility and attractiveness to pollinators.

A cyathium can, however, consist solely of male or female flowers, in which case it is referred to as unisexual. 

Not all Euphorbia species exhibit the characteristic structure of cyathia typical of the genus. For instance, species previously classified under Pedilanthus, which has since been subsumed into Euphorbia, are notable exceptions. However, such instances are relatively rare.

Finally, euphorbias can be dioecious (unisexual), with male and female cyathia on separate plants, or monoecious, featuring male, female, or bisexual cyathia on the same plant, depending on the specific species. 

Meet some remarkable South African euphorbias

Succulent euphorbias exhibit a remarkable and bewildering diversity of growth forms, ranging from low-growing perennials to substantial trees, some reaching heights of 15 metres or more. Many species possess spines and are consequently often mistaken for cacti due to their similar appearance, despite the fact that they are not related and belong to a completely different plant family. 

South Africa, in particular, boasts a rich diversity of succulent Euphorbia flora, which can be attributed to the country's exceptionally varied climatic zones and habitats. Notable examples include the following species:

Euphorbia bupleurifolia

Figure 2. Euphorbia bupleurifolia, resembling a pine cone or a small cycad, is highly sought after by collectors and is regarded as being at an extremely high risk of extinction in its natural habitat.

Figure 3. Euphorbia bupleurifolia (encircled in red) is frequently encountered in grassland habitats, where it can be challenging to find.

Figure 4. A juvenile specimen of Euphorbia bupleurifolia.

This highly ornamental species is endemic to the eastern provinces of South Africa, specifically the Eastern Cape and KwaZulu-Natal.

Euphorbia bupleurifolia is a bisexual, spineless, dwarf succulent that attains heights of 40–200 mm. The usually unbranched, reddish-brown stem is erect and varies in shape from globose to cylindrical, measuring 25–70 mm in thickness. It is entirely covered with numerous tubercles, which create a resemblance to a pine cone or a small cycad, thus leading to its common names: cycad spurge or pine cone plant. The bluish-grey-green, non-succulent leaves, which are shed during the dry season, are elongated and narrow, widening towards the tip, and are tufted around the apex of the stem and branches.

The specific epithet bupleurifolia (also referred to as the species epithet or epitheton) is derived from Latin and Greek roots and translates approximately to 'having leaves like Bupleurum,' a genus belonging to the Apiaceae (carrot family).

Euphorbia clandestina

Figure 5. The leafy upper region of the stem of Euphorbia clandestina, with bisexual cyathia concealed between the bracts.

Figure 6. Euphorbia clandestina plants, reaching up to 1 metre in height, growing with support from shrubs on a rocky hill.

Figure 7. Euphorbia clandestina plant about 40 cm tall.

This attractive, bisexual, spineless succulent is native to the semi-arid regions of the Western Cape, where it grows in karroid scrub and renosterveld vegetation on stony slopes and plains. It exhibits a columnar growth habit, characterised by a single, erect stem typically measuring between 30 and 60 cm in height, occasionally reaching up to 120 cm, and up to 70 mm in diameter. The pale green stem, often mottled with purple or dark green, is usually unbranched, either cylindrical or club-shaped, and studded with prominent, warty outgrowths or tubercles. If the stem is damaged at its apex, branches may develop around the affected area; however, most plants tend to remain unbranched. The linear leaves are restricted to the upper region at the stem’s apex.

The species epithet clandestina is of Latin origin, signifying 'hidden' or 'concealed.' It pertains to the stalkless hermaphroditic cyathia, which are concealed among a double row of purple and green leaf-like structures known as cyathophylls, or cyathial leaves, that encircle them.

Euphorbia clandestina is commonly known as volstruisnek in Afrikaans, a term that translates literally to 'ostrich neck,' referring to the plant’s erect, warty, cylindrical stem.

Euphorbia esculenta

Figure 8. An aged Euphorbia esculenta plant, approximately 30 cm in diameter.

Figure 9. Euphorbia esculenta plants in their natural habitat in the Great Karoo. Inset: Bisexual cyathium of Euphorbia esculenta.

This striking species is endemic to the Eastern Cape, occurring in the semi-arid region of the Great Karoo. It is a typical representative of the so-called 'Medusa's head' or 'medusoid' euphorbias, a group of somewhat weird, yet nevertheless fascinating spurges characterised by numerous branches radiating from the main stem in a radial pattern. These plants are thought to resemble Medusa, the terrifying figure from Greek mythology with living snakes in the place of hair, hence the common name.

In Euphorbia esculenta, the plant develops a thick central stem or caudex with many snake-like branches, some up to 20 cm long, that spread out in a rosette shape near the top. This species can grow up to half a metre wide, making it one of the most conspicuous among the 'medusoid' Euphorbia species. Its central stem can rise as high as 30 cm above the ground. This happens partly because soil erosion sometimes exposes the stem, but in areas with very hard soil, there is very little stem below ground level. Other nearby plants of this species sometimes have stems that stay below the surface, which suggests that soil conditions affect whether the stem is exposed (Bruyns, 2022). 

The epithet esculenta means 'edible' or 'fit to eat' in Latin, indicating that the plant was once considered edible for humans. As noted by the German botanical explorer, plant collector, and natural historian Ferdinand Krauss (1846): 'When peeled, they have the shape of our kohlrabi and a similar taste; enjoyed raw, they leave a slightly scratchy sensation in the throat. However, when roasted in ashes or, better yet, cooked with meat, they are tolerable.' Nonetheless, I would personally refrain from consuming this plant.

Farmers have also regarded this species as a useful plant, feeding its nutritious tuberous roots and dried cores to livestock, particularly in years of drought.

Euphorbia meloformis

Figure 10. Euphorbia meloformis in its natural surroundings, displaying an unusually broad growth habit, with a diameter of approximately 20 cm.

Figure 11. The Euphorbia meloformis plant shown here is notably elevated above the ground, rather than being closely pressed to it, which is typical for the species.

Figure 12. Euphorbia meloformis, a larger male specimen approximately 12 cm in height, displays persistent, hardened inflorescence stalks that are notably elongated, with a seedling positioned below on the right.

Figure 13. The plant depicted is somewhat controversial. While some botanists consider it synonymous with Euphorbia meloformis, others regard it as a distinct species, Euphorbia valida. Euphorbia valida can be distinguished from Euphorbia meloformis by several characteristics, most notably its tendency to grow larger and develop a cylindrical stem with age, reaching heights of up to 30 cm and diameters of 12.5 cm. 

Another remarkable species endemic to the Eastern Cape is Euphorbia meloformis. The specific epithet meloformis is derived from Latin, in which melo refers to 'melon' and formis means 'shaped like' or 'in the form of'. Thus, meloformis translates to 'melon-shaped,' a designation that is particularly apt for this species.

Euphorbia meloformis possesses a single, swollen, prominently angled, and typically hemispherical spineless stem, exhibiting considerable variability in thickness, which generally ranges from 3 to 10 cm but may occasionally reach a diameter of 20 cm or more. The stem usually remains closely pressed to the ground or may even be slightly sunken into it. In natural environments, the stem rarely branches from the base or higher. However, plants in cultivation tend to branch more frequently. This dwarf succulent is predominantly unisexual but can occasionally be bisexual (Bruyns, 2022).

Due to its unusual and attractive melon-shaped appearance, the species ranks among the most popular and sought-after specimens of Euphorbia among succulent plant collectors and horticulturalists.

Euphorbia namaquensis

Figure 14. Close-up of Euphorbia namaquensis plants. The specimen on the left measures 30 cm in height without branches and approximately 40 cm in height with branches, exhibiting a base diameter of approximately 27 cm.

Figure 15. Euphorbia namaquensis, a monoecious species with hermaphroditic cyathia.

Figure 16. Bisexual cyathia of Euphorbia namaquensis.

Figure 17. Euphorbia namaquensis exemplifies the capacity of euphorbias to grow in seemingly inhospitable environments, including some of the hottest and driest landscapes in South Africa. One such location is situated south of Vioolsdrift in the Northern Cape, as illustrated in this photograph.

This is an additional species within the group of medusoid euphorbias. Although it may not be as conspicuous as Euphorbia esculenta, E. namaquensis also features a primary stem adorned with numerous densely crowded branches.

The species name namaquensis typically means 'from Namaqualand' or 'of Namaqualand,' referring to the Namaqualand region, a semi-arid to arid area located in Northern Cape in the north-west of South Africa and southernmost Namibia. However, to the best of current knowledge, the plant is only native to, or commonly found in, the region of South Africa south of the Orange River.

This subtly medusoid Euphorbia usually develops a single, erect, cylindrical main stem upon maturity, reaching heights of up to 30 cm. The stem is densely covered with small, rounded, wart-like projections known as tubercles. Relatively short branches, extending up to 12 cm in length, emerge from the axils of these tubercles, projecting towards the apex of the plant, thereby imparting a somewhat shaggy appearance to this bisexual plant. 

Euphorbia obesa

Figure 18. A female Euphorbia obesa plant in its natural habitat, bearing fruit.

Figure 19. The initially hemispherical stem of Euphorbia obesa may become cylindrical with age, and in its natural habitat, these elongated plants often lean to one side, as illustrated in this photograph.
The author's wife's hand served as a size reference. The plant was approximately 12 cm long.

Figure 20. Rarely observed in nature: a branched Euphorbia obesa plant, likely the result of damage to the apex. The plant leans close to the ground.

This species is native and endemic to the Eastern Cape, which is renowned for its abundance of euphorbias. Euphorbia obesa shares several morphological characteristics with the closely related E. meloformis, notably in its reduction to a single swollen main stem. It is thus not surprising that Peter MacOwan, then the curator of the Cape Town Botanic Gardens, who discovered this peculiar succulent in 1897, sent it to the Royal Botanic Gardens in Kew under the name Euphorbia meloformis. There, however, the plant was identified as a previously unknown species and subsequently named and described as Euphorbia obesa by Joseph Dalton Hooker in 1903.

This is a unisexual, spineless species characterised by a single, unbranched primary stem that is initially subglobose or nearly spherical but becomes cylindrical with age, often tending to lean to one side.

This stem typically exhibits eight flattened ridges and can reach a height of approximately 20 cm and a width of about 9 cm. It is grey-green to brown in colour and is adorned with numerous horizontal, dull purple transverse bands.

Euphorbia obesa is among the most striking and conspicuous species of succulent Euphorbia, perhaps even the most notable. It is highly sought after by succulent enthusiasts for its attractive appearance and is arguably the most popular Euphorbia species in succulent collections worldwide. Shortly after its discovery in 1897, unscrupulous collectors exploited wild populations, rendering it one of the first native South African species to face a very high risk of extinction as early as 1915.

The specific epithet obesa comes from Latin and means 'fat' or 'plump.' In the context of Euphorbia obesa, it refers to the plant's round, swollen, or chubby appearance, which resembles a small, plump ball.

Euphorbia polygona

Figure 21. An attractive variety of Euphorbia polygona with an epidermis covered with a brilliantly white layer of a waxy coating (Euphorbia polygona var. nivea). Inset: Male cyathia of  Euphorbia polygona var. nivea.

Figure 22. A particularly spiny, cactus-like variety of Euphorbia polygona (Euphorbia polygona var. major) in its natural habitat.

Figure 23. This photograph depicts the typical form of Euphorbia polygona.

Figure 24. Another variety of Euphorbia polygona, which also has an attractive white epidermis, is known as Euphorbia polygona var. alba. Compared to Euphorbia polygona var. nivea, however, this variety has a more compact growth habit and its cyathia have green nectar glands instead of purple ones.

This impressive, barrel-shaped, usually dioecious succulent shrub, commonly known as the 'African Milk Barrel,' is often mistaken for a cactus. There are 12 distinct natural varieties and it is perhaps the most morphologically diverse species in the genus Euphorbia (Schnabel, 2022). It is a popular choice for gardens and greenhouses and is frequently available in various forms at nurseries.

Euphorbia polygona is a multi-angled succulent, as its species name suggests. The epithet has Greek origins, derived from poly, meaning 'many,' and goni (or gona), meaning 'angle.' The plant forms clumps of predominantly spiny stems of varying sizes, reaching up to approximately 2 metres in height and between 4 and 30 cm in diameter. The colour of the involucral glands of the usually unisexual cyathia ranges from red to dark purple or yellow-green to green, while the epidermal coloration varies from pale green, green, bluish-green, and bluish-grey to greenish-grey, occasionally displaying striking horizontal light and dark grey-green stripes or a distinctly white, powdery, waxy coating.

Euphorbia polygona is native to the Eastern and Western Cape provinces of South Africa.

Euphorbia zoutpansbergensis

Figure 25. Euphorbia zoutpansbergensis growing on a rocky sandstone slope of a hill, in a sunny northeast-facing aspect. Inset: A juvenile Euphorbia zoutpansbergensis.

Figure 26. Euphorbia zoutpansbergensis generally possesses a solitary, erect stem. However, the plant may also exhibit multi-stemmed growth, as illustrated in this photograph.

This notable spurge is a representative example of the tree-like euphorbias indigenous to South Africa. It is a bisexual, usually single-stemmed succulent tree that reaches heights of 2–5 metres, distinguished by a large, nearly spherical crown composed of densely packed, slender branches that bear sharp spines along their angles.

The specific epithet zoutpansbergensis refers to the species’ occurrence in the Zoutpansberg, a mountain range located in the Limpopo Province of northeastern South Africa. The term 'Zoutpansberg' reflects an archaic Dutch spelling of 'Soutpansberg,' the Afrikaans name meaning 'Salt Pan Mountain.'

Threats and Conservation

Although highly resilient, many succulent euphorbias are seriously threatened by the reduction in the amount of space available for their survival and reproduction. Urban expansion, mining, agriculture, and overgrazing by livestock have contributed significantly to the deterioration of their natural habitats. However, the most urgent threat—not only to succulent euphorbias but to all succulent plants—is illegal collection for the international horticultural trade in Europe, the USA, and especially Asia. This illegal trade has escalated dramatically in recent years (Kriel, 2023; Trenchard, 2022) and has a substantial impact on South Africa and its neighbouring countries, that together are home to approximately 45% of the world's known succulent species. Recently, illegal collection in South Africa has become a large-scale operation, with plant seizures increasing by over 250% annually (Smith et al., 2023). Between 2021 and 2023, nearly 1.5 million succulents, covering approximately 650 species, were removed illegally from the wild without permits, resulting in a sharp decline in local populations. Consequently, commercial poaching has emerged as a critical conservation issue (Kriel, 2023; Smith et al., 2023). Many succulent species, including euphorbias such as Euphorbia bupleurifolia, Euphorbia meloformis, and Euphorbia obesa, are now threatened with extinction in their native habitats (Bruyns, Raimondo, & Dold, 2022; Raimondo et al., 2022).

The protection of these unique plants necessitates concerted conservation efforts. South Africa's legal framework, including the National Environmental Management: Biodiversity Act, provides some degree of protection, although improved enforcement and habitat restoration are essential. Conservation organisations, botanical gardens, and researchers are collaborating to cultivate endangered species and raise awareness of the importance of conserving these plants in their natural environments.

 

References

Bruyns, P. V. (2022). Euphorbia in southern Africa: Volume 1. Springer International Publishing AG.

Bruyns, P. V., Raimondo, D., & Dold, A. P. (2022). Euphorbia obesa Hook.f. National assessment: Red list of South African plants version. Retrieved October 29, 2024, from http://redlist.sanbi.org/species.php?species=574-4025 

Krauss, F. (1846). Beiträge zur Flora des Cap- und Natallandes. Regensburg.

Kriel, G. (2023, September, 11). How farmers can combat succulent poaching. Farmer’s Weekly Magazine. Retrieved October 29, 2024, from https://www.farmersweekly.co.za/opinion/by-invitation/how-farmers-can-combat-succulent-poaching/

Radcliffe-Smith, A. (2001). Genera Euphorbiacearum. Richmond (GB ): Royal Botanic Gardens Kew.

Raimondo, D., Dold, A. P., Berrington, W., Archer, R. H., Victor, J. E., von Staden, L., & Mhlongo, N. N. (2022). Euphorbia meloformis Aiton.   National assessment: Red list of South African plants version. Retrieved   October 29, 2024, from http://redlist.sanbi.org/species.php?species=574-4072

Schnabel, D. H. (2022). A monograph of Euphorbia polygona from the perspective of an amateur botanist (2nd ed.). Haan: D.H. Schnabel

Smith, G.F., Figueiredo, E., Victor, J. & Klopper, R.R. (2023): Plant poaching in southern Africa is aided by taxonomy. Is a return to Caput bonae spei inevitable? Taxon 72(4): 717–723.

Trenchard, T. (2022, May 4): South Africa’s plant poaching epidemic. Geographical. Retrieved October 29, 2024, from https://geographical.co.uk/wildlife/south-africa-plant-poaching-epidemic

About the author: 

Detlef H. Schnabel was born in 1958 in Düsseldorf, Germany.  Detlef is a German amateur botanist with a profound passion for the captivating succulent plants of South Africa. Since 2014, he has served as the national representative of the International Euphorbia Society (IES) for Austria and Germany, and in 2024, his role was expanded to include South Africa. He regularly contributes to Euphorbia World, the IES journal, sharing insights from his research. In 2021, Detlef was honoured by the IES with the ‘Daphne Pritchard Memorial Award’ for the best article published in Euphorbia World between 2018 and 2020. Since his retirement in 2018, Detlef has spent five to six months every year in George, a town on South Africa's Garden Route. From there, he continues his focused research on South African euphorbias, contributing to a deeper understanding and appreciation of these remarkable plants.