Acacia xanthophloea Benth.

The fever tree is an attractive, semi-deciduous to deciduous tree approximately 15 to 25 meters tall and has an open, rounded to spreading or flattish crown which is sparsely foliated. The characteristic, almost luminous, lime green to greenish-yellow bark is smooth, slightly flaking, and coated in a yellow powdery substance described by some as sulphurous. If the powdery surface is rubbed away with the finger it will reveal a green bark beneath. Young twigs have a red-brown bark which peels off leaving the twigs sulphur yellow. The long straight white thorns are arranged in pairs and although they are very significant on young trees they often become barely noticeable on mature specimens.

Bright yellow, golden, ball-like flowers which are sweetly scented are borne in clusters on shortened side shoots at the nodes and towards the ends of branches. Flowering occurs from August or September to November. Flowers are followed by the production of yellowish- brown to brown pods which split open to reveal the small hard brown seeds, which may be harvested from January to April.

The genus name Acacia is derived from the greek word acantha meaning spine, thorn or prickle and the species name xanthophloea is derived from the greek words xanthos meaning yellow and phloios meaning bark.

The fever tree occurs mainly in depressions and shallow pans where underground water is present or surface water collects after summer rains. It is also found in low-lying swampy areas, along the margins of lakes and on river banks. It often forms pure, dense stands of closed woodland in seasonally flooded areas on alluvial soils. This tree can be found from Kenya in the north to KwaZulu Natal in the south. It is a prominent feature in the lowveld region of South Africa.

This tree is popular amongst birds for nest building as the thorns add extra protection against predators such as snakes. Young branches and leaves are eaten by elephant and the leaves and pods are eaten by giraffe and vervet monkeys. Monkeys and grey louries also eat the flowers. The gum and green seeds are eaten by baboons. Insects such as bees are attracted by the yellow colour and sweet scent of the flowers and perform a pollination role.

The wood is hard, heavy and a suitable general purpose timber but it should be seasoned before use otherwise it is likely to crack. The main stems and larger branches are used to fence out hippo from fields on the Pongola floodplain and the timber is reputed to be used for boxwood. Medicinally the bark is used for treating fevers and eye complaints.

Early pioneers thought that this tree caused a fever since people travelling or living in the areas where it grew contracted a bad fever. They therefore associated the fever with the tree. This however was erroneous as the swampy places where fever trees grow are also ideal breeding grounds for mosquitoes, which carry malaria. Thus through these early settlers the myth was born and the plant acquired its name as the fever tree.

Growing Acacia xanthophloea

The fever tree is an exceptionally attractive tree and is often used to decorate gardens and urban landscapes. Its contrasting bark, feathery foliage, and architectural attributes make it an eye-catcher and thus suitable as a focal point in a landscape. A fast growth rate of
approximately 1.5 m per year under ideal conditions make this plant a good candidate for gardeners and landscapers who want quick results.

This plant has root nodules containing nitrogen fixing bacteria as do most members of the Mimosaceae family and these play an important role in the nitrogen enrichment of soils which then has a positive impact on the growth of plants around the fever tree. The dappled shade underneath the canopy is ideal for smaller plants which require protection from the full brunt of the suns rays but still require sufficient light.

The fever tree is relatively easy to propagate. Before sowing, the seed should be soaked in hot water overnight. This causes the seeds to swell and usually by the next morning they are ready to be sown. Seed can be sown in seedling trays using a well drained seedling medium and then covered lightly. When the seedlings reach the two-leaf stage (approx. six to eight weeks after sowing) they should be transplanted from seedling trays into nursery bags, taking care not to damage the long taproot. Seedlings and young trees transplant well. Seed and young growing plants are available at selected seed stockists and nurseries respectively.

Due to its mature dimensions it is recommended not to plant it close to buildings. This tree can tolerate moderate frost and can often be seen in cultivation in the cooler areas on the highveld such as certain parts of Johannesburg and Pretoria.

Acacia xanthophloea belongs to the pod bearing family Fabaceae. There are 40 species , subspecies and varieties of Acacia represented in South Africa. Many species such as the fever tree have leaflets which fold up at night. A special feature of this family is the pulvinus which is a conspicuous thickening at each petiole and petiolule base which allows the leaves to close at night and also during extreme heat. Stipules (or a stipular scar) are always present and are often modified into thorns or spines as is the case with the fever tree.

The genus Acacia is mostly confined to Africa where almost all have stipular spines or recurved thorns. It is also found in Australia where most are without thorns. Acacias are conspicuous , particularly in drier areas, becoming dominant in many vegetation types and are important fodder trees with useful wood, gum, and bark. Acacias are also host to many butterfly species which have specialised in feeding on the flowers pods or leaves.

References

• Coates Palgrave, K. 1983 Trees of Southern Africa. Struik: Cape Town.
• Johhson, D. & Johnson S.1993 Gardening with Indigenous Trees and Shrubs. Southern Book Publishers (Pty) Ltd.
• Smit, N. 1999 Guide to the Acacias of South Africa. Briza: Pretoria
• Pooley. E 1993. The complete field guide to Trees of Natal, Zululand & Transkei. Natal FloraPublications Trust: Durban.
• Trendler, R. & Hes, L. 1994. Attracting Birds to your Garden in southern Africa. Struik Publishers (Pty)Ltd.: Cape Town.
• Venter, F & Venter J. 1985 Making the Most of Indigenous Trees. Briza Publications:Pretoria.
• Van Wyk, B, & van Wyk, P. 1997 Field Guide to Trees of Southern Africa. Struik: Cape Town.

Andrew Hankey & Marc Stern
Witwatersrand National Botanical Garden
March 2002