© Henry Brisse
Tamarix usneoides is an evergreen shrubby tree of semideserts and karroid areas, with short scaly trunk, leafy branches usually extending from ground level, scaly leaves and cream-white flowers.
Tamarix usneoides is a perennial shrub or small tree 0.6–6.09 m tall; crown upright, narrow, somewhat columnar or narrowly conical; plants usually found in dense stands. Stems short, scaly. Branches leafy, usually extending from ground level; branchlets almost drooping. Bark brown-grey, rough, glabrous when older, longitudinally fissured. Leaves 1.25 mm long, greyish green, with salt glands, scale-like, vaginate (base clasping the stem or branch), closely overlapping, with short to inconspicuous herbaceous point. The plants are rarely dioecious.
Tamarix usneoides branches
Inflorescence loose to more or less densely composed of slender axillary sprays or racemes. Flowers very small, pale, cream-white; petals inequilateral, 2.25 mm long, elliptic-ovate; sepals entire, outer sepals smaller, ovate-acute, inner sepals bigger, trullate-ovate; bracts similar to leaves, vaginate, shorter than to slightly exceeding pedicels (flower stalks); pedicels half as long as sepals; corolla persistent. Flowering in summer, July to October, sometimes in January, February and May. Fruit is a capsule, ovoid, about 6 mm long, dehiscent. Each flower can produce thousands of tiny (1 mm diameter) seeds that are contained in a small capsule and are usually decorated with a tuft of hair at the apex.
Tamarix usneoides flowers
T. usneoides is usually deep-rooted; tap roots are able to harvest water from deeper in the soil profile, may reach 30 m in depth; spreading adventitious roots are often produced when a plant is buried by shifting dunes and may reach a length of 50 m.
Illustrated diagram of T. usneoides
Click for larger image
According to SANBI's Threatened Species Programme T. usneoides is of Least Concern status.
Distribution and habitat
Tamarix usneoides is distributed in the semidesert and karoo areas of the southwestern region of South Africa in the Northern Cape, Western Cape and Eastern Cape provinces, and in Namibia. It occurs along river banks, dry or temporary river beds and pans with subterranean, often brackish water, on sandy and salty dunes and flats, and in rocky deserts, at altitudes of 90–1 370 m.
Derivation of name and historical aspects
Linnaeus altered the name Tamaricus of Tournefort to Tamarix, a classical Latin name for trees of the genus. The genus Tamarix is native to drier parts of Africa, Asia and Europe, and consists of about 50–60 species. In South Africa the genus is represented by T. usneoides. Pure stands of T. usneoides are difficult to find because the species hybridizes with alien species.'. There are three alien species in southern Africa: T. chinensis, T. parviflora and T. ramosissima, which are now naturalized in the arid parts of the country. These aliens have a more rounded crown, sessile leaves and pale to dark pink flowers. The hybrid of T. usneoides and T. ramosissima occurs in Western Cape and also in Namibia. It looks more like the latter, with flowers that might look creamish but in fact have a tint of pink and, as in T. ramosissima, it has long prominent bracts and long internodes.
|| Tamarix usneoides hybrid flowers Photo: Alex Dreyer
Many species of the genus are known to be troublesome due to their invasive habits and because they compete with neighbouring plants for water resources. Tamarix plants are xerophytic trees or shrubs. They have long tap roots that allow them to intercept deep water tables and exploit natural water resources. They are highly tolerant of various stressful conditions such as heat, cold, drought, floods, and high concentrations of dissolved solids. Tamarix is an adaptable halophytic genus, tolerant of highly saline habitats. It is able to limit competition from other plants by taking up salt from deep ground water through the roots, accumulating it in their leaves, exuding the excess concentrated salts through glands in the leaves and dropping them, causing a situation of increased surface soil salinity. By this temporal alteration of the environment it inhibits the development of native plant species. The salt is washed away from the soil surface during heavy rains. Tamarix is fire-adapted; it has a high foliar water and salt content making it difficult to burn. Fire increases flowering and seed production. When fire does occur, Tamarix resprouts readily from its root crown and rhizomes. The seeds are contained in a small capsule and are usually adorned with a tuft of hair at the apex that aids in dispersal by wind. Seeds can also be dispersed by water.
Uses and cultural aspects
The leaves provide fodder to livestock. Wood is used mainly for firewood. The genus is an efficient windbreaker, excellent dune binder, used for ornamentation, serves as hedges under desert or dry conditions, or near seashores, used for fixation of river banks to prevent erosion; it is tolerant of salt spray, and known to contain high amounts of tannin.
Tamarix usneoides in habitat
Photo: Alex Dreyer
Growing Tamarix usneoides
Tamarix usneoides is rarely seen in gardens, while alien and hybrid Tamarix species with pink flowers are widely grown as ornamentals and sometimes mistaken for T. usneoides. The grower may recognise T. usneoides by its cream-white flowers, and vaginate, scaly leaves. Tamarix can spread both vegetatively, by adventitious roots and sexually, by seeds. Tamarix trees are most often propagated by cuttings. Seedlings require extended periods of soil saturation for establishment. The trees can tolerate a wide range of environmental conditions once established.
References and further reading
- Baum, B.R. 1978. The genus Tamarix. The Israel Academy of Sciences and Humanities, Jerusalem.
- Foden, W. & Potter, L. 2005. Tamarix usneoides E.Mey. ex Bunge. National Assessment: Red List of South African Plants version 2011.1. Accessed on 2011/09/12.
- Germishuizen, G., Meyer, N.L., Steenkamp, Y. & Keith, M. (eds) 2006. A checklist of South African plants. Southern African Botanical Diversity Network Report 41. SABONET, Pretoria.
- Van Wyk B.P. & B.-E. 2000. Photographic guide to trees of southern Africa. Briza Publications. Pretoria.
Pretoria National Herbarium