Obetia tenax (N.E.Br.) Friis
Common names: mountain nettle, rock tree-nettle, tree nettle, giant nettle, stinging nettle tree (Eng.); bergbrandnetel, rotsbrandnetel (Afr.); lebati (Northern Sotho); lutiya, lusotfo (Swazi); mbhadzwa (Tsonga); mmabi, moralejwe, more-walentswê (Tswana.); muvhazwi, dyambila, gukhunya, muendana-thavha, muungana muvhazwi (Venda); umbabazane, uluza (Xhosa); uluzi, umdadi-omkhulu, impongozembe, imbati (Zulu)
SA Tree No: 70
An awesome small tree with the most striking flowers and leaves with stinging hairs, that can be cooked and eaten as a vegetable.
Obetia tenax is small, deciduous, succulent tree or shrub, which grows 2 to 7 m tall. The main stem is smooth, bark is brown to pinkish bronze, with prominent lenticels and releases clear sap when peeled.
Many long stinging hairs are found mainly on the younger branches, and on leaves, twigs and flowers. Leaves are alternate, large, ovate, 35–130(–170) × 35–115(–190) mm, light green, soft, succulent, with a serrated margin and a long petiole, 40–140 mm.
Flowers are greenish yellow to white, borne in branched clusters and are usually produced before the leaves, in late winter to spring (Aug. –Sept.).
Bare trees in flower are conspicuous. The sexes are separate, and are borne on separate plants. Fruits are tiny, held in papery flower remains, in early summer (Oct. –Nov.) and the fruit does not open to release seeds.
According to the Red List of South African plants, Obetia tenax is assessed as Least Concern (LC) and is not threatened.
Distribution and habitat
Obetia tenax occurs naturally in the KwaZulu-Natal, Limpopo, Eastern Cape, Gauteng, Mpumalanga and North West Provinces. It is not endemic to South Africa, and also occurs in Swaziland, Botswana, Zimbabwe and Mozambique. It grows on dry rocky hillsides, among loose stones, sometimes near streams, in forest, thornveld and valley bushveld.
Derivation of name and historical aspects
The derivation of the genus name Obetia is unknown. The species name tenax means ‘tenacious’ or ‘strong’.
Bees are all over the plant during flowering season and even nest in hollows in the base of the stem. Only Black Rhino browse the stems and leaves and it is a food plant for the Pale-yellow Acraea and Dusky Acraea butterflies.
Obetia tenax bark produces a strong fibre and is traditionally used to make cord or rope, for thatching and for making sleeping mats. The leaves are cooked and eaten as morogo, a kind of spinach. It is also used in traditional medicine. The hairs cause intense burning irritation and can cause blisters on the skin. In the garden, it makes a good barrier plant and is an attractive bonsai subject.
Growing Obetia tenax
This plant can be easily propagated by seeds or cuttings. The growing medium for seed propagation is 3 parts sand and 1 part compost, in a seed tray. Sow in spring or early summer and place in the greenhouse with 30% shade netting. Water moderately until the seeds germinate. It is relatively fast-growing. Plant it in full sun, in well-drained soil and water moderately in summer.
- Boon, R. 2010. Pooley's trees of eastern South Africa, a complete guide. Flora & Fauna Publications Trust, Durban.
- Burrows, J., Burrows, S., Lotter, M. & Schmidt, E. 2018. Trees and shrubs of Mozambique. Print Matters Heritage
- Drummond, R.B. 1975. A list of trees, shrubs and woody climbers indigenous or naturalised in Rhodesia. Kirkia 10(1): 238.
- Hutchings, A., Scott, A.H., Lewis, G. & Cunningham, A.B. 1996. Zulu medicinal plants: an inventory. University of Natal Press, Pietermaritzburg.
- Palmer, E. & Pitman, N. 1972. Trees of southern Africa. Balkema, Cape Town.
- Raimondo, D. et al. 2009. Red list of South African plants. Strelitzia 25. SANBI (South African National Biodiversity Institute), Pretoria.
- Schmidt, E., Lötter, M. & McCleland, W. 2002. Trees and shrubs of Mpumalanga and Kruger National Park. Jacana, Johannesburg.
- Setshogo, M.P. 2005. Preliminary checklist of the plants of Botswana. Sabonet Report no. 7. Sabonet, Pretoria and Gaborone
Sephatle Evans Molekoa
Lowveld National Botanical Garden
Plant Type: Shrub, Tree
SA Distribution: Eastern Cape, KwaZulu-Natal, Limpopo, Mpumalanga, North West
Soil type: Sandy, Loam
Flowering season: Spring, Early Summer
Flower colour: White, Pink
Aspect: Full Sun
Gardening skill: Easy