Pelargonium vanderwaltii Van Jaarsv.
Common names: Otjihipa pelargonium (Eng.); Otjihipa malva (Afr.)
A rare, cliff-dwelling perennial, known only from sheer, south-facing cliffs of the Otjihipa Mountains in the Kaokoveld of northern Namibia. It is a cliff-squatter, forming solitary shrublets in crevices against the cliff. It grows fairly well in cultivation, best as a pot plant, and flowers in summer.
Pelargonium vanderwaltii is a perennial, succulent to semi-succulent shrublet, up to 180 mm tall and 300 mm in diameter, much and irregularly branched, quite compact, winter-deciduous and slightly aromatic. The roots are fibrous. The ascending, rounded stems are 5–10 mm in diameter, green at first, becoming reddish brown, dark brown and smooth with age. The surfaces of young branches are covered with soft, white hairs (sericeous), becoming hairless (glabrescent) with age. The leaves are simple, crowded at the tips and ascending. The leaf blades are broadly egg-shaped to almost round 15–30(–50) × 25–38(–65) mm, the base heart-shaped (cordate). The margins are toothed (dentate), sinuate, and with a row of hairs (ciliate). The upper and lower surfaces are covered with soft hairs, the lower surface with prominent veins. The leaf tip is rounded. The petiole, 40–100 mm long, is persistent, drying to grey-white. The stipules are also persistent, triangular, 2 × 3 mm. The inflorescences are terminal, producing a 3-flowered pseudo-umbel, 50–70 mm in diameter; the peduncle short, 5–10 mm long, and the flower stalks 20 mm long. The sepals are linear-lanceolate, 5.0 × 1.5–2.5 mm, acute. The 5 petals are spoon-shaped (spathulate), rounded at the ends, varying from dark to pale mauve. The stamens, with 2 shorter, bearing white pollen. The seed (mericarps) is 5 mm long, the tail 12 mm long.
Pelargonium vanderwaltii although rare, is not endangered due to its remote, safe, cliff-face habitat, ensuring its long-term survival.
Distribution and habitat
Pelargonium vanderwaltii is known only from Kaokoveld in northwestern Namibia and adjacent to the Kunene River, bordering Angola to the north. It grows on sheer, south-facing, granitic rock crevices of the Otjihipa Mountain, at an altitude of 1 500–1 900 m. The twin peak, where the plants grow, is locally known by the Himba as Okahukumune. P. vanderwaltii grows on southern aspects of the western peak. The vegetation is semi-arid, sharing its habitat with other species such as Aeollanthus haumanii. The vegetation on this mountain consists mainly of Commiphora-Cyphostemma Savanna. Rainfall in the habitat is sparse and ranges from 75–100 mm per annum and is experienced mainly in summer, in the form of thunder showers. The winters are dry, cooler and with occasional fog from the Namib Desert.
Derivation of name and historical aspects
Pelargonium vanderwaltii was named by Braam van Wyk and the author in 2006, in the journal Aloe. Pelargonium vanderwaltii was named in honour of Adri van der Walt (1938–2003), late professor of Botany at the University of Stellenbosch. Adri’s main work in botany was the on the genus Pelargonium and the 3-volume work that he produced together with artist Ellaphie Ward-Hilhorst, treated many species of Pelargonium (Glen & Germishuizen 2010). This species was first collected by Mr Pieter Winter, botanist from the South African National Biodiversity Institute, on an expedition to the Otjihipa Mountains with Mr and Mrs Thompson from Haenertsburg. The plant was visited in its habitat on a subsequent by the author (E.v.J.) on an expedition investigating the cliff faces in the Kaokoveld region, and additional material gathered, upon which the plant was grown, illustrated and named.
Pelargonium vanderwaltii belongs to section Cortusina DC., representing 20 species. This section has short, thick, fleshy stems, armed with persistent stipules. Most of these are confined to Namaqualand and southern Namibia. P. vanderwaltii has the northernmost distribution in the north of Namibia.
Pelargonium vanderwaltii is pollinated by insects. Solitary plants grow in crevices of the cliff and the south-facing cliffs provide ideal protection from larger herbivores. However, when damaged by mammals, such as the Chacma Baboon, the plants simply resprout. The succulent nature of the stems, ensure its long term survival in spite of dry conditions. In winter the plant becomes deciduous. The seeds are oblong-obovoid, attached to a spirally twisted awn. Seeds are dispersed by wind in autumn, during the onset of the summer rains. Once landed on a suitable crevice, the twisted awn of the seed unwinds with moisture, and forces the seed into the substrate.
No uses have been recorded.
Growing Pelargonium vanderwaltii
Pelargonium vanderwaltii is best for dry, semi-desert, warm-temperate gardens (Van Jaarsveld 2010). The plant is easily grown in a hot, dry climate and best propagated by cuttings. Cuttings ranging from 60–100 mm long, root rapidly in moist sand in summer. A rooting hormone is not required. The plants grow slowly. It is best planted in a mineral-poor, sandy, acidic soil, in light shade. Ample compost should boost its performance.
Pelargonium vanderwaltii can be grown both as a container plant or in dry, semi-desert gardens (Van Jaarsveld 2010), where frost is absent or light. It should preferably be grown on dry stone walls or rockeries. It is best grown in well-drained sandy soil and an annual compost dressing will improve its growth performance. In cooler climates, it should rather be grown in a heated greenhouse and kept dry in winter. When grown in containers, the plants should be protected from frost. They are fairly pest-free, but will rapidly rot if kept too wet or in poorly drained soil.
- Glen, H.F. & Germishuizen, G. (compilers). 2010. Botanical exploration of southern Africa, edition 2. Strelitzia 26. South African National Biodiversity Institute, Pretoria.
- Van Jaarsveld, E.J. & Van Wyk, A.E. 2006. Pelargonium vanderwaltii, a new cliff dwelling species from the Otjihipa Mountians, northern Namibia. Aloe 43 2 & 3: 32–34.
- Van Jaarsveld, E.J. 2010. Water wise gardening. Struik, Cape Town.
E.J. van Jaarsveld
Kirstenbosch National Botanical Garden (Retired)
Extraordinary senior lecturer and researcher, Department of Biodiversity and Conservation, University of the W. Cape.
Plant Type: Succulent
Soil type: Sandy
Flowering season: Late Summer
Flower colour: Mauve/Lilac
Aspect: Full Sun, Morning Sun (Semi Shade)
Gardening skill: Challenging