Euphorbia umfoloziensis Peckover
Common names: Umfolozi euphorbia (Eng.); (some euphorbias are commonly known as umhlonhlo in isiZulu)
In a hot river valley in northern KwaZulu-Natal, this rare, spiny, dwarf succulent can be found. It has only ever been recorded from this one river valley. Euphorbia umfoloziensis boasts inflorescences with bright, canary-yellow flowers, known as cyathia, and has a carrot-like root with a thickened stem.
Fig. 1. An adult Euphorbia umfoloziensis in cultivation showing thickened body and angled branches.
Euphorbia umfoloziensis is a long-lived, low-growing succulent plant that has both the root and thickened stem underground. The root is seldom branched and ends in a taproot, giving rise to secondary roots. The stem branches sideways, developing several heads, which are separated from the root by extended depressions where old branches have fallen off. The stem apex gives rise to 10–20 aerial stems, which are about 50–80 mm long and are bluish-green with lighter green markings. The tubercles have paired spines, which are thin, V-shaped and may have basal prickles. The spine shield may either be continuous or discontinuous. Euphorbia umfoloziensis has numerous inflorescences on new growth, with a solitary cyathium at the flowering eye. This cyathium can either be male or bisexual and is canary-yellow. The fruit is an obtusely trilobed capsule, which is sessile within the involucre, while the seed is subglobose and has a diameter of approximately 3 mm. The seed is variegated with light and dark brown. The flowering season for E. umfoloziensis is unknown, however, the peak flowering time for most other euphorbias in a similar climate is late winter and spring.
Fig. 2. Section of Euphorbia umfoloziensis branch showing characteristic paired spines.
Euphorbia umfoloziensis is closely related to E. vandermerwei, which occurs in the Mpumalanga province. These species both possess a single cyathium at the flowering eye whereas other euphorbias have a cyme of 3 cyathia. Their branches are also not spiralled like other euphorbias. The main difference between these two species is the thickened tap root of E. umfoloziensis, while E. vandermerwei has a fibrous type of root. The colour of the cyathia and the capsule is another difference, with E. vandermerwei having a reddish cyathium and a red capsule with spherical locules whereas E. umfoloziensis has a canary-yellow cyathium and a green capsule with a shade of red.
The Red List of South African plants currently classifies Euphorbia umfoloziensis as Vulnerable (VU) under the criteria D2. Threats to this species include habitat degradation due to trampling of seedlings and overgrazing, and the illegal harvesting of plants by succulent enthusiasts. All succulent euphorbias, including E. umfoloziensis, are included in CITES Appendix II.
Distribution and habitat
Euphorbia umfoloziensis is confined to only two localities in the Umfolozi River valley in KwaZulu-Natal. The plants were found growing in groups on well-drained, red sandy loam, on north facing slopes of the river valley, with only the branches exposed. The veld type of both localities is Valley Bushveld and these sites fall under the Savanna Biome in the Zululand Lowveld vegetation type. As these sites are lower than 800 m above sea level, the temperatures in summer can get extremely hot, reaching a maximum of 40°C. Plants of this species can tolerate high surface temperatures as the northern slope orientation exposes them to concentrated solar radiation. While the winters are cool, frost is unlikely to occur in this region.
Derivation of name and historical aspects
The genus name Euphorbia was assigned by Carl Linnaeus to commemorate Euphorbus who was a physician to King Juba II of Mauretania. The specific epithet, umfoloziensis, refers to where the species occurs, in the Umfolozi River valley. The common name spurge that is given to euphorbias is derived from the French word espurgier, meaning ‘to purge’, which gives an indication of the properties of the Euphorbia latex when ingested.
The genus Euphorbia belongs to the large, cosmopolitan family Euphorbiaceae. Approximately 200 species in the family Euphorbiaceae occur in South Africa. The genus Euphorbia is the third largest genus of flowering plants in the world, consisting of more than 2 000 species, which vary in habit. The genus has been divided into sections based on the uniqueness of growth forms of these plants. They vary from small geophytes, annuals or perennial herbs, to shrubs or trees. In southern Africa alone there are about 20 species of tree euphorbias, reaching heights of up to 18 m. Roughly 1 300 members of the genus are herbs, or typical spurges, with herbaceous branches only. The shrubby species are found in semi-arid lands of many countries, particularly in Africa and America. About 850 Euphorbia species have evolved the succulent habit; with most of these being African species. The succulent euphorbias occur in India, Arabia, Africa, the Canary Islands and Madagascar.
Euphorbia umfoloziensis is closely related to E. vandermerwei and allied to E. enormis, E. persistens, E. groenewaldii and E. tortirama.
Fig. 3. A fruiting Euphorbia umfoloziensis plant in cultivation and a close-up of the trilobed seed capsule and the characteristic, mottled, light and dark brown seed.
Euphorbias have reduced, unisexual flowers but sometimes the female and male flowers are fused in a cyathium. While plants of some Euphorbia species are bisexual, the plants of others are either male or female and plants of both sexes are required to produce seed. Many plants with bisexual flowers can self-pollinate, thereby resulting in selfing or autogamy. Self-fertilization is more common in annual plants whereas cross-fertilization is more prevalent for perennial plants. Some species have self-incompatibility mechanisms which prevent self-fertilization. In certain Euphorbia species, the female flower of the cyathium develops first, which prevents pollination by the pollen from the male flowers within the same involucre. Another strategy is the positioning of the ovary above the reach of the male flowers. The fertilization of winter-flowering plants when few or no insects are available suggests that self-fertilization is the norm within this genus. The cyathium glands produce nectar, and pollination is mainly by flies or other small insects while certain species depend on the force of wind or explosive dehiscence of the anther cells to transmit pollen. Upon successful pollination, the ovaries will develop into dry capsules filled with seeds. These will rupture when ripe, scattering the seed.
Although there are no recorded medicinal uses for Euphorbia umfoloziensis, many species of Euphorbia are widely known for their medicinal properties. These species treat a multitude of diseases and ailments such as skin ulcers, toothaches, haemmorrhoids, warts, cancer tumours and intestinal parasites. Some species, like E. hirta, possess insecticidal properties and have been used effectively against fruit flies, weevils, bugs, beetles and aphids. Many Euphorbia species are used as arrow and fish poison in many African countries, because the latex is extremely toxic. Some non-toxic euphorbias are used as fodder for livestock. However, the main uses of Euphorbia species are horticultural due to their showy bracts and often brightly coloured foliage. The smaller, succulent euphorbias have also become increasingly popular as pot plants and overtrading is causing a decline in the number of wild species. As a result, the succulent species of the genus Euphorbia are included in the Appendices to the Convention on International Trade In Endangered Species Of Wild Fauna And Flora (CITES).
Fig. 4. A young Euphorbia umfoloziensis specimen in cultivation.
Growing Euphorbia umfoloziensis
Euphorbia plants are relatively easy to propagate from seed or cuttings. Seed is the best way of propagation. Euphorbia seeds are released by an explosive dehiscence, so it is advisable that one covers the seed capsule with a stocking or fine net while waiting for the seeds to be released. Germination of Euphorbia seeds should ideally take place during warm weather. Euphorbia seeds generally take about 14 days to germinate. A seedling mixture suitable for Euphorbia seedlings contains 4 parts fine river sand, 4 parts coarse river sand, 1 part sieved, well-rotted compost, 1 part perlite and 1 part vermiculite. The seedlings should not be grown in full sunlight and the seedling mixture should not be overwatered but should always remain slightly damp.
When growing euphorbias from cuttings, this should ideally be done during the warmer months (December to February in South Africa). Most of the branched, miniature species such as E. umfoloziensis can be propagated in this way. Euphorbia cuttings should have the cut ends either sealed with a tree sealer or should be dusted with sulphur, the smaller ones should be left to dry out. The cuttings should be left for a few weeks to dry out. The cuttings should then be rooted in coarse sand or a sandy medium and kept dry until the roots start to form. Once the roots have appeared, the cuttings may be watered once a day during very hot weather.
The soil is probably the most important aspect in ensuring successful propagation. The most ideal medium would be soil from their natural environment. However, since this is not always possible, it is best to use soil that is as close to the natural environment as possible. The recommended potting mixture for euphorbias contains: 4 parts fine river sand, 2 parts course river sand, 4 parts sieved, well-rotted compost, 1 part perlite, 1 part vermiculite and 1 part coconut fibre. The soil pH should be between 6.5 and 7.5 and good drainage is very important.
Aloe marlothii and Euphorbia pulvinata are good companion species for Euphorbia umfoloziensis as these were present in one of the sites in which this species was discovered.
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Nokukhanya Nozipho Mhlongo
Threatened Species Unit, Pretoria National Botanical Garden
Plant Type: Succulent
SA Distribution: KwaZulu-Natal
Soil type: Sandy, Loam
Flowering season: Winter
Flower colour: Yellow
Aspect: Full Sun
Gardening skill: Easy