Adromischus diabolicus
Introduction
Adromischus diabolicus is a rare, cliff-hugging succulent from the Northern Cape. The plants are dwarf, rosulate, leaf and stem succulents forming small mats, the leaves green to dull greyish green and yellowish-green tubular flowers with reddish-purple lobes in summer. Best grown in containers.
Fig. 1. A close-up of a cluster of the cliff-hugger, Adromischus diabolicus at Aggeneys, Northern Cape. Note the dried fruiting follicles.
Description
Description
Dwarf-sized, densely branched, compact, cluster-forming and cliff hugging plant, up to 50 mm high, 250 mm in diameter, from a tuberous rootstock. Branches green at first, becoming grey, up to 3 mm in diameter. The leaves 15–20 × 7–17 mm, brittle, obovate to broadly obovate or rarely rounded, grey-green to green, immaculate, biconvex, or flat during drought. The margin is entire and horny with blunt leaf tips. The surface has a flaking, waxy layer, apex obtuse, rounded to truncate and the base wedge-shaped. Plants only sparsely flowering, the inflorescence a spike-like monochasium up to 150 mm long, bearing 1–3 pedicellate flowers, the pedicel(s) 5–10 mm long. The calyx up to 3.5 mm long. The corolla 12.5–14.0 mm long with a funnel-shaped tube, yellowish green, and the floral lobes reddish-purple on the upper surface, ovate-triangular, 2.5–3.5 mm long, with club-shaped hairs in the throat, the apices acute. The anthers included. Flowering is in early summer (November–December).
Fig. 2. An illustration of a plant in flower in habitat at Aggeneys, Bushmanland by Marieta Visagie.
Conservation Status
Status
Adromischus diabolicus was assessed as Rare in 2009 and Data Deficient in 2015 by the Red List of South African Plants. It is widespread and not threatened, the plants are safeguarded by its difficult to reach habitat and its distribution falls within a greater conservation region.
Fig. 3. The south-facing cliff-face habitat of Adromischus diabolicus north-east of Aggeneys, Bushmanland, Northern Cape (left). (right) A close-up of Adromischus diabolicus filling a vertical crevice on the cliff, showing the tangled, articulated stem tubers.
Distribution and habitat
Distribution description
Confined to the Northern Cape where it grows in the mountains along the Orange River from the south-eastern end of the Richtersveld to near Pofadder in the east. Plants grow in crevices and on ledges on gneiss and quarzite of the Karoo Supergroup (Johnson et al. 2006). The rugged mountainous terrain of the lower Orange River Valley has many ledges, crevices and fissures, ideal for establishment of plants. Adromischus diabolicus grows mainly on the cooler, south-facing aspects at an altitude of 500–900 m. Plants are rooted in, proliferate and fill crevices, the cluster size often depending on the growing space allowed by the crevice. The climate is very hot in summer, with an average daily maximum temperature of 26–28°C and an average daily minimum 13–15°C. During summer it is not uncommon to reach 45°C. Winters are mild without frost. Rainfall is mainly in autumn and spring and occasionally at other times of the year, about 50-100 mm per annum falls in the form of thunder showers or cyclonic winter rain.
The associated vegetation consists of Eastern Gariep Rocky Desert (Desert Biome) (Mucina & Rutherford 2006). Associated cliff-dwelling plants include Conophytum fulleri, Crassula exilis subsp. sedifolia, Pelargonium xerophyton, Cotyledon orbiculata, Tylecodon rubrovenosus, Ornithogalum sp., Aloidendron dichotomum, Crassula sericea var. velutina, Crassula elegans, Adromischus alstonii, Crassula muscosa, Anacampseros ruschii, Kleinia longiflora and Jamesbrittenia ramosissima.
Fig. 4. The mountains at Aggeneys, Northern Cape, habitat of Adromischus diabolicus. Plants only grow on sheer south-facing cliffs, this photo taken at the end a long drought in Bushmanland.
Derivation of name and historical aspects
History
Adromischus diabolicus was named by Helmut Toelken in Bothalia in 1979 from plants collected by horticulturist Pieter Drijfhout from the Stellenbosch University Botanical Garden. Pieter collected his plants near the Blesberg Mine in Bushmanland. The Latin species name diabolicus pertains to the very hot, inhospitable, diabolical desert climate of this lower portion of the Orange River. The common name Gariep adromischus pertains to its habitat, the lower Orange River, Gariep is a Khoikhoi word meaning ‘great’ or ‘large’ and is another name for the Orange River, the largest of the rivers in South Africa.
Adromischus diabolicus is one of 6 species of Adromischus that belong in section Brevipedunculati, established by Carl von Poellnitz in 1940 to accommodate those species characterised by funnel-shaped, glaucous-green (rarely pink) corolla tubes that are slightly grooved at their ends, and with minute club-shaped hairs on the inner surfaces of lobes and throats. The colour of the lobes varies from white to dark mauve and rarely orange (A. phillipsiae). Other members of this section include A. caryophyllaceus, A. fallax, A. phillipsiae and A. nanus. Of these, A. diabolicus, A. nanus and A. fallax are associated with cliffs.
Adromischus diabolicus is closely related to A.nanus from quartz hills just north east of Steinkopf. Adromischus nanus grows in exposed habitats and is not mat-forming. It is also a dwarf, but less branched plant. Adromischus diabolicus was illustrated by botanical artist Marieta Visagie from plants collected by the author in Bushmanland.
For those interested in Adromischus, see Adromischus, the Cactus File Handbook published in 1998 by John Pilbeam, Chris Rogerson and Derek Tribble.
Fig. 5. Large cliff hugging clusters of Adromischus diabolicus on south-facing cliff faces in Bushmanland, north-east of Aggeneys, Northern Cape, (left) after rain (right) during the dry season.
Ecology
Ecology
Adromischus diabolicus proliferates forming dense, cliff-hugging mats from a tangled tuberous base. It is mainly confined to shady, sheltered south-facing cliffs or boulders. Moisture is stored in the succulent stems, leaves and tubers. The plants have a slow, conservative growth and are long-lived perennials which can withstand long periods of drought. The leaves grow ascending-spreading, green in shady crevices becoming greenish-brown during periods of drought. Most of the population grows out of reach of herbivores, however the dassie or rock rabbit (Procavia capensis) will graze the plants during periods of drought.
Fig. 6. A cluster at Aggeneys that has been damaged by dassies or rock rabbits (Procavia capensis) that graze and damage the plants where they can get access to the plants.
The leaf margin is entire, lacking the horny, stiff margin of most other species of Adromischus. Compared to other non-cliff relatives, there is a reduction in armament, a response to the undisturbed cliff habitat. The stoloniferous nature enables a vegetative propagation back-up, allowing the plant to colonise new crevices and maximising its long term survival on the cliff.
The plant produces only a few flowers but what it lacks in flowers it makes up for in its dense vegetative growth. The inflorescence grows ascending to spreading, the corolla with dark purplish-reddish lobes that are probably adaptated to a specific flying insect for pollination. The capsules release the seed in autumn, coinciding with the autumn or winter rainfall. Moisture is retained longer in the substrate during this cooler time of the year thus providing the best chance of germinating. The seed is minute and light, and is shaken from the capsules, dispersed by wind, and is ideal for establishment in crevices.
Fig. 7. A close-up of a small cluster of the Adromischus diabolius showing the flaking waxy leaf surface and a dried fruiting follicle.
Uses
Use
No medicinal or cultural uses have been recorded.
Growing Adromischus diabolicus
Grow
Plants are easily grown but best in small containers and are ideal in miniature succulent container gardens grown with other cliff dwelling plants such as Crassula exilis subsp. sedifolia, Haworthiopsis tessellata and Tylecodon sulphureus var. armianus. It grows best in dappled shade in a sandy to gritty soil. Plants should be watered only sparingly during autumn and spring. Plants rapidly respond to watering, becoming turgid, dividing rapidly, forming dense clusters and filling the containers. Plants can be fed with a mild solution of organic fertiliser throughout the year. Its very easy growing nature maximises its survival rate. Plants adapt well to small rock-filled containers.
Fig. 8. Adromischus diabolicus in habitat on a sheer, south-facing cliff in the Northern Cape. (left) A vertical crevice filled with a plant after sufficient rainfall. (right) A plant at the end of a long drought.
Plants are easily propagated by division or stem cuttings in late summer, and are not too difficult in cultivation. Avoid over watering as plants tend to rot.
Sow seed in autumn or spring in a shallow tray in a sandy mixture and keep moist. Germination is within 3 weeks and once large enough to handle, transfer to individual containers. Place container in a shady position but with full light. The south side of a building is ideal.
Plants are relatively disease free, except for root rot with too much watering, but aphids, vine weevils, slugs and snails can sometimes be a problem.
References
- Johnson, M.R., et al. 2006. Sedimentary rocks of the Karoo Supergroup. In M.R. Johnson, C.R. Anhaeusser & R.J. Thomas (eds), The geology of South Africa: 463–501. Geological Society of South Africa, Johannesburg Council for Geoscience, Pretoria.
- Mucina, L. & Rutherford, M.C. (eds) 2006. The vegetation of South Africa, Lesotho and Swaziland. Strelitzia 19. South African National Biodiversity Institute, Pretoria.
- Pilbeam, J., Rodgerson, C. & Tribble, D. 1998. Adromischus. The Cactus File Handbook 3. Cirio Publishing Services, Southampton.
- Raimondo, D., Von Staden, L., Foden, W., Victor, J.E., Helme, N.A., Turner, R.C., Kamundi, D.A. & Manyama, P.A. (eds) 2009. Red list of South African plants. Strelitzia 25. South African National Biodiversity Institute, Pretoria.
- Toelken, H.R. 1985. Crassulaceae. Flora of Southern Africa 14: 1–229.
- Toelken, H.R. 1979. CRASSULACEAE: Three new taxa and a new combination. Bothalia 12(4):633-634.
- Von Poellnitz, K. 1940. Zur Kenntnis der Gattungen Cotyledon L. und Adromischus Lem. Feddes repertorium specierum novarum regni vegetabilis, Zeitschrift für systematische Botanik 48: 80–113.
- Von Staden, L. 2015. Adromischus diabolicus Toelken. National Assessment: Red List of South African Plants version . Accessed on 2024/05/22.
Credits
Ernst van Jaarsveld
Kirstenbosch National Botanical Garden (Retired)
Babylonstoren Farm (Current)
Extraordinary senior lecturer and researcher,
Department of Biodiversity and Conservation, University of the Western Cape
May 2024
Acknowledgements: the author thanks colleagues Cornell Beukes and Nico van Wyk for assistance in the field.
Plant Attributes:
Plant Type: Succulent
SA Distribution: Northern Cape
Soil type: Sandy
Flowering season: Early Summer
PH: Acid
Flower colour: White, Pink
Aspect: Shade, Morning Sun (Semi Shade)
Gardening skill: Average
Special Features:
Drought resistant
Horticultural zones
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