Delosperma zeederbergii L.Bolus
Common names: Spekboom River mesemb (Eng.); spekboomriviervygie (Afr.)
Delosperma zeederbergii is only known from cliffs along the upper Spekboom River near Lydenburg (Mashishing) in Mpumalanga. A fast grower, it has soft flaccid growth, from a more compact centre, becoming sprawling, with linear lanceolate leaves and attractive dark purplish-pink flowers. It is a cliff-squatter and can be used as a pot plant or hanging basket. The leaves are slightly grooved at the top and keeled at the base.
Fig. 1. Delosperma zeederbergii in habitat on a sheer, south-facing cliff face at about 2 000 m above sea level, at Swartkop Forrel Oord near Lydenburg, on 5 January 2005. Note the grassveld in the backround (Lydenburg Mountain Grassland). The plant is towards the end of its flowering season with swollen young fruiting capsules developing, and shares its habitat with Aloe arborescens, Crassula lanceolata and a young Crassula sarcocaulis in the background.
Delosperma zeederbergii is a lax, decumbent, soft and flaccid, summer growing, succulent shrublet to about 250 mm in diameter, the stems radiating from a short, somewhat compact central growth and tuberous rootstock. The roots are fibrous. The stems die back partially during winter, the resting phase, when the plant becomes more compact. The branches with internodes 30-40 mm long, reddish brown and 2 mm in diameter. The leaves are somewhat flattened and linear lanceolate to subterete, gracefully recurved 30-50 x 3-5 mm, the upper surface channelled the lower surface keeled and the apex acute. The leaf surface is minutely papillate. The juvenile leaves of the compact phase are ovate lanceolate and shorter than the adult leaves. The flowers are about 25–30 mm in diameter, opening during the day, and closing at night; pedicels papillate, 12-18 mm long. Petals up to 15 x 1.2-3 mm broad purplish pink. Filamentous staminodes present becoming pale, the anthers and pollen straw-coloured. Flowering is mainly in spring and summer.
Fig. 2. Delosperma zeederbergii in flower in its habitat, growing on south facing cliffs at Spekboom River, Mpumalanga in January 2005. It shares its habitat with Crassula lanceolata and a species Streptocarpus.
Not common and only known from the upper reaches of the Spekboom River, the plants are well protected by the sheer cliffs and, therefore, are not threatened. The 2006 assessment for the Red List of South African Plants lists it as Data Deficient – Insufficent Information (DDD), known only from the type specimen, however the author has observed it growing on many cliffs in the region, and found plants on cliffs at 1 500 m and again at 2 000 m and infers that they most probably also grow at sites in-between.
Fig. 3 The Spekboom River at Doringhoek, cliff-face habitat of Delosperma zeederbergii.
Distribution and habitat
Delosperma zeederbergii is only known from the upper Spekboom River between 1 500 and 2 000 m above sea level, growing on cliffs. It is found on the farm Doringhoek, about 5 km upstream from the bridge (Lydenburg Burgersfort Road) at about 1 500 m to 2 000 m at the Swartkop Forrel Oord. It was located on two separate occasions by the author in January 2005 and July 2022.
At the Swartkop Forrel Oord, at about 2 000 m altitude, plants were found in January 2005 on sheer south facing cliffs. The plant grows on ledges and shares its habitat with other species such as Aloe arborescens, Cotyledon orbiculata, Haemanthus humilis, Crassula lanceolata, Crassula sarcocaulis, Crassula setulosa var. deminuta, Senecio oxyriifolius, Plectranthus verticillatus. Taller shrubs in the habitat include Halleria lucida, Dais cotinifolia, Cephalanthus natalensis and Protea roupelliae. The associated vegetation is Lydenburg Mountain Grassland of the Grassland Biome (Mucina et al. 2006).
Fig. 4. The Spekboom River has cut a gorge through in the hard sandstone rock, forming the cliff-face habitat of Delosperma zeederbergii. Note the Helichrysum kraussii shrubs and occasional Cussonia paniculata var. sinuata in the grassland.
Along the Spekboom River, closer to the bridge, on the farm Doringhoek, plants were observed in July 2022 growing in Lydenburg Doringveld of the Grassland Biome (Mucina et al. 2006). The plants were observed on cliffs adjacent to the river on both sides. The cliff and rocky steep sides here with plants mostly a mosaic of the Savanna & Grassland biome and include species such as Berchemia discolor, Bowkeria cymosa, Ficus glumosa, Ficus burkei, Ficus sur, Ficus ingens, Ficus abutiilifolia, Greyia sutherlandii, Commiphora marlothii, Englerophytum magalismontanum, Cussonia spicata and Cussonia transvaalensis. On the cliffs, Delosperma zeederbergii shares its shallow crevice habitat with plants such as Aeollanthus buchnerianus, Aloe arborescens, Aloe spicata, Crassula expansa subsp. fragilis, Crassula setulosa, Crassula swaziensis, Haemanthus humilis, Cyanotis speciosa, Kalanchoe sexangularis, Kalanchoe rotundifolia, Plectranthus verticillatus, Coleus ramosior, Senecio barbertonicus and Senecio oxyriifolius.
Fig. 5. Left: The cliff-face habitat at Spekboom River, July 2022, although no spekboom (Portulacaria afra) grows here, Senecio barbertonicus and rock splitting figs (Ficus abutilifolia) also grow on the cliff. Right: Delosperma zeederbergii growing in a rock crack on an exposed north face. Note the shorter compact flat purplish brown leaves and seed capsules from the previous season.
Plants usually grow on mineral-poor, quarzitic sandstone cliffs. The aspect on the north and west face is exposed but the southern cliffs, where most plants grow, are protected from excessive sunlight and the rocks also hold the moisture longer. Plants are rooted in crevices of ledges, occasionally becoming drooping over the rock faces. Temperatures are moderate to cold in winter, the average daily maximum about 18°C and average daily minimum for the region 10°C. Winters are cool but frost is absent or light. Rainfall is mainly in summer, ranging from 800 to 1 500 mm per annum.
Derivation of name and historical aspects
Delosperma zeederbergii was first collected on 13 March 1933 by Mr M. Zeederberg and at more or less the same time by Ernest Galpin (1858-1941), a well known botanist who sent cuttings to Kirstenbosch National Botanical Garden where it was grown on (Garden accession number 433/33 NBG). When it came into flower October 1933 it was illustrated by the botanical artist B.D. Carter. The four Zeederberg brothers, of Swedish descent, were well-known for their Zeederberg Coach Company, a horse-drawn mail and stage coach which operated during the late 1800s and early 1900s and petered out after the Anglo Boer War. The younger brother, Pieter Frederick Martin Zeederberg (-1942), is thought to be person after whom the plant is named.
Fig. 6. A plant of Delosperma zeederbergii on a south facing moist cliff together with ferns and liverwort, at Doringhoek, Spekbomrivier, July 2022. Note the shorter compact flat leaves.
Delosperma zeederbergii was named by Louisa Bolus in 1934 in her Notes on Mesembryanthemum and allied genera (p. 422) from the Zeederberg collection and additional plant material provided by Ernest Galpin. The next collection was by the author in January 2005 at the Zwartkop Forrel Oord above the Spekboomrivier (NBG 102/05) as part of the author’s research on cliff-dwelling succulent plants. In 2007 the Mpumalanga Plant Specialist Group also searched for Delosperma zeederbergii from the bridge and upstream but was unsuccessful (Agenbag 2007). In July 2022 the farm Doringhoek, Spekboomrivier was visited to look for Spekboom (Portulacaria afra) by a team of botanists and ecologists. Although the Portulacaria afra could not be found, Delosperma zeederbergii was found at three sites on both sides of the river.
Delosperma zeederbergii belongs to a soft, flaccid-stemmed group from the summer-rainfall grassland region. Although perennial, they have a limited life span of 3-5 years and new populations are established from seed. The other closely related species include D. soutpansbergensis (endemic to the Soutpansberg) and D. waterbergensis (endemic to the Waterberg), all summer-growing, obligatory cliff dwellers, growing on the cooler, south-facing cliffs in mineral poor, quarzitic sandstone soil.
Fig. 7. A Delosperma zeederbergii plant growing in a rock crack on an exposed north face at Doringhoek, Spekbomrivier, July 2022. Note the shorter compact leaves and mature seed capsules on the previous season’s growth.
The plants grow firmly rooted in crevices and on ledges. The succulent leaves enable the plant to withstand periods of drought. The fine pointed papillae, apart from storing moisture, assist with trapping dew and fog. Fog in summer is not uncommon on the Mpumalanga Escarpment Mountains and provides additional moisture. The plant is a rapid grower from a central rootstock, the fast growing flowering branches die back during the dry winter months, but the central portion remains intact, sprouting again in spring. The younger juvenile leaves are shorter ovate lanceolate and often becoming purplish, caused by the betanin pigment which helps slow down photosynthesis during the dry period.
Fig. 8. A close-up of the leaves of Delosperma zeederbergii in cultivation at Babylonstoren Farm, the plants collected from the farm Doringhoek, Spekboomrivier.
The flowers are pollinated by bees and other small insects. The seeds are retained in the hygrochastical capsules and are only released during periods of rain, when the capsule’s expanding keels force open the cell lids and the seeds are dispersed when the falling raindrops splash them out of its capsule. Delosperma fruiting capsules do not have covering membranes, as are found in many other mesembs (hence the name delos=naked and sperma=seed). However upon drying, the cell lids are closed again contracting keels conserving the seed until the next rain shower.
Fig. 9. Delosperma zeederbergii with purplish-pink flowers, in cultivation at Babylonstoren Farm, November 2022 (plants collected at Doringhoek, Spekboomrivier).
Delosperma zeederbergii can be grown as an ornamental succulent plant. It is easily grown in containers and in gardens outside of its habitat provide it is in well-drained soil in a cool, shady position.
Fig. 10. A plant of Delosperma zeederbergii in cultivation at Babylonstoren Farm, originally collected at Doringhoek, Spekboom River).
Growing Delosperma zeederbergii
Although Delosperma zeederbergii is easy to grow, and despite being a succulent, it needs regular watering during the summer months, at least 3 times a week. Best grown in a container and placed on a south facing aspect. It is tolerant of dappled shade. The plant reacts well to organic fertilisers such as seaweed-based liquid fertilizers or compost and is best for cool grassland gardens (Van Jaarsveld 2010). Due to its specialized cliff habitat, which it shares with few species, it cannot compete with more aggressive growing plants so take care not to let it get overgrown by companion plants in the garden. They grow rapidly and should flower during the first season. It is adapted to grow on mineral poor quarzitic sandstone soil. At Babylonstoren Farm plants are grown in ceramic containers in shady conditions.
Propagate from stem cuttings 7-12 cm long in summer or autumn, remove the lower leaves and plant the stems to a depth of about 1-4 cm in a sandy mixture. Keep moist until well rooted.
Plants grow well in a general succulent mixture, such as 2 parts sand, 1 part garden loam and 1 part well broken down compost. It is adaptable to other soils but good drainage is essential and regular moisture during the summer months.
- Agenbag, L. 2007. Not finding Delosperma zeederbergii. Crew News Volume 4 p.17. Available for download at https://www.sanbi.org/wp-content/uploads/2018/04/crewewsletter-december2007.pdf
- Bolus, L. 1934. Delosperma zeederbergii in Notes on Mesembryanthemum and allied Genera, page 422.
- Burgoyne, P.M. 2006. Delosperma zeederbergii L.Bolus. National Assessment: Red List of South African Plants version 2020.1. Accessed on 2023/02/01.
- Hartmann, H.E.K. 1991. Mesembryanthema. Systematics, biology and evolution of some South African taxa. Contributions from the Bolus Herbarium. No. 13: 75–157.
- Hartmann, H.E.K. 2001. Aizoaceae A–E. In Eggli, U. & Hartmann, H.E.K. (eds.), Handbook of succulent plants. Springer. Heidelberg, New York, etc.
- Lavis, M. 1969. Notes on the genus Delosperma (Mesembrieae). Journal of South African Botany 35: 145–147.
- Mucina, L. & Rutherford, M.C. (eds) 2006. The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, Pretoria.
- Van Jaarsveld, E.J. 2010. Waterwise gardening in South Africa and Namibia. Struik, Cape Town.
Ernst van Jaarsveld
Kirstenbosch National Botanical Garden (Retired 2015)
Extraordinary senior lecturer and researcher,
Department of Biodiversity and Conservation, University of the Western Cape
Acknowledgements: the author thanks Anso Le Roux for her help in arranging the Spekboom expedition to Mpumalanga and Limpopo, as well as for providing information on the Zeederberg family and copies of the type specimen; and Tommy Steyn and Frik Bronkhorst for assistance in the field and arranging the help of the farmer at Doringhoek, Spekboomrivier, Lydenburg.
Plant Type: Shrub, Succulent
SA Distribution: Mpumalanga
Soil type: Sandy
Flowering season: Spring, Early Summer, Late Summer
Flower colour: Pink
Aspect: Full Sun, Morning Sun (Semi Shade), Afternoon Sun (Semi Shade)
Gardening skill: Easy