This Tree may reach 30m high with a vertically fissured bark. Simple Leaves are discolorous and toothed near the apex. Tiny yellow Florets are dioecious. Fruit is a small cypsela with attached bristles.
Brachylaena transvaalensis, Brachylaena discolour subsp. transvaalensis.
RSA Tree No. 731.
Common name: Forest Silver-oak.
Family: Asteraceae – Compositae (Daisy family: includes sunflowers, lettuce, chicory, marigolds). There are in excess of 1 900 genera and close to 33 000 species. This is possibly the second biggest plant family. In southern Africa, there are 246 genera and about 2 300 species. Local genera containing trees include Brachylaena, Oldenburgia and Tarchonanthus. Some members have flowers grouped in heads and the whole head may appear to be a single flower – like the “sunflower”. Surrounding each flower are bracts. Individual Flowers have sepals replaced by a pappus which may be bristle, plume, scale or awn like. Individual flowers are called Florets, which may have 5 fused petals. The inferior Ovary contains one Ovule and the Style has 2 lobes.
Name derivation: Brachylaena – short cloak – referring to the short floral bracts. transvaalensis – referring to location in the old province – Transvaal.
Conservation Status: L C. (Least Concern). 2009 (Raimondo et al.).
The Tree is up to 30m high. The Trunk is single, straight and up to 30cm+ in diameter. The plant is usually solitary or may occur in small groups. The initially smoothish Bark is grey or brown-grey. It ages to become vertically fissured and stringy. Pale, raised Lenticels (a usually raised corky oval or elongated area on the plant that allows the uncontrolled interchange of gases with the environment), which may run lengthwise, are visible on the hairless young branches.
The tree may be briefly deciduous. The Leaves are dark green above and have dense whitish hairs below. The leaves are spirally arranged, simple (has a single blade which may have incisions that are not deep enough to divide the blade into leaflets) and may be wavy. Each leaf is narrowly elliptic and usually about 8 x 4cm or larger. The veins are sunken above but protrude below, where they are more clearly visible. The lateral veins end in a rough V-shape before reaching the margin. The Margin is entire, apart from close to the apex – where it is irregularly and sharply toothed. It may be rolled under. The Apex is tapering to acuminate (said of an acute apex whose sides are somewhat concave and taper to a protracted point – like a drip-tip). The Base is narrowly tapering and runs partly down the 5mm long Petiole (leaf stalk).
The yellow Florets (Flowers) are in Capitula (Flowerheads). The florets are individual flowers, mainly in Asteraceae and grasses that, together, make up a dense form of inflorescence. The unisexual florets are dioecious (male and female flowers on the different trees). A cylindrical 5-lobed Corolla tube is present. The Male Capitula have 11-16 florets. The Anthers are filiform (thread or filament like). Bracts occur in 3-7 rows. The Receptacle (is that expanded tip of the flower stalk from which the floral parts develop and is greatly expanded in the Asteraceae and Ficus) is honeycombed, and slightly convex. The Ovary is usually absent. A Pappus (modified outer perianth series of Asteraceae, borne on the ovary and it may be bristle, plume, scale or awn like) is present. In this case, it has a single row of scabrid (having a rough or scaly surface) bristles. The Female Capitula has up to 8 florets in large axillary and terminal Panicles (indeterminate, branched inflorescence with stalked flowers) which are up to 16cm long. The Involucre (one or more whorls of small leaves or bracts standing underneath a flower or flower-cluster) is round to cup-shaped. There are 4-6 rows of bracts extending to the base of the stalk. The ribbed, single chambered Ovary is ovoid to oblong. It has an apical tuft of scabrid bristles in a single row. (Jul-Sep).
The Fruit is a small Cypsela (in Asteraceae it is a dry single-seeded fruit formed from a double ovary of which only one develops into a seed) or nutlet. Here the pappus (modified outer perianth series) has several rows of creamy brown bristles present. (Sep-Nov).
Distribution & Ecology
The Tree is located in evergreen and deciduous forests as well as wooded grasslands in KwaZulu-Natal – along the escarpment, Mpumalanga, Limpopo and Swaziland. The Nectar attracts insects including bees. Insectivorous or carnivorous birds that visit the Trees include Flycatchers, Shrikes and Prinias. Bushbuck and Kudu browse the Leaves.
The hard, tough and fine-grained Wood is used for implement handles, boat building, fence posts etc. Propagation is through seeds or cuttings. The Roots are non-evasive. The tree grows best in full sun and is frost hardy. Aqueous extracts from the plant have shown some antibacterial activity.
Boon, R. 2010. Pooley’s Trees of eastern South Africa. Flora and Fauna Publications Trust, Durban.
Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of Southern Africa, edn 3. Struik, Cape Town.
Lawrence, G. H. M, 1951. Taxonomy of Vascular Plants, The Macmillan Company, New York. Tenth Printing 1965.
Palmer, E. & Pitman, N. 1972. Trees of southern Africa, Balkema, Amsterdam, Cape Town.
Schmidt, S. Lotter, M. & McCleland, W. 2002. Trees and Shrubs of Mpumalanga and the Kruger National Park.
van Wyk, B. & van Wyk, P. 1997 Field guide to Trees of Southern Africa, Struik, Cape Town.