This Tree may reach 8m high. The opposite Leaves are simple. Dioecious trees has capitula with the small yellow Florets on the receptacle. Fruit is a cypsela. The pappus has an apical tuft of bristles to aid wind dispersal of the 1 small, light Seed.
Brachylaena rotundata, Brachylaena discolour var. rotundata, Brachylaena rhodesiana.
RSA Tree No. 730.
Common names: Mountain Silver Oak, Highveld Silver-oak, Bosvaalbos, Bergvaalboom.
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. rotundata – with roundish leaves.
Conservation Status: L C. (Least Concern). 2009 (Raimondo et al.).
This Tree may reach 8m high or it may develop as a shrub. The Trunk has a diameter of up to 20cm. The plant is usually solitary or may develop in small groups and often Branches low down. These branches tend to droop. The Bark is dark, blackish or brown-grey and deeply grooved when old. The usually slender, smooth and grooved Twigs (1-year-old current branch segments) are initially covered with white hairs but slowly become purplish or reddish-brown and hairless. Pale, raised, visible Lenticels (a usually raised corky oval or elongated area on the plant that allows the uncontrolled interchange of gases with the environment) may run lengthwise (photo 180).
The alternatively arranged Leaves are narrowly elliptic, ovate (shape of an egg) or oblong and up to 16 x 6cm. They are larger on coppice (a thicket or grove of small trees or shrubs, especially one exposed to periodic burning, cutting or pruning) growth. The tree may be deciduous depending on the temperature. Rubbing the Upper surface of mature leaves exposes a glabrous (hairless) dark green colour. This dark green becomes more apparent on older leaves as they lose hair. Soft hairs cover the much lighter Lower surface. The protruding Midrib and lateral veins are clearly visible. The Apex is rounded to broadly tapering and may be toothed. It may be minutely mucronate (ending in a short, sharp abrupt hair-like tip). The Base tapers or is almost rounded. The Margin is often entire or roughly and irregularly toothed – especially closer to the apex. The short Petiole (leaf stalk) is up to 7mm long.
The Flowerheads are early blooming and the yellow Florets (individual flowers mainly in Asteraceae and grasses that make up a dense form of inflorescence) may precede the new leaves. They are arranged in dense round clusters in short terminal Panicles (indeterminate, branched inflorescences with stalked flowers) 4-40cm long or in short raceme-like panicles in the axils of fallen leaves. Here these florets are Dioecious (male and female flowers on the different trees). The Involucre (whorl/s of small leaves or bracts just below the flower) is cup-shaped with 5-8 rows of bracts. These decrease in size further down to the base of the Pedicel (stalk of a single flower in a cluster). The Receptacle is that expanded tip of the flower stalk from which the floral parts develop. It is greatly expanded in the Asteraceae and Ficus. It is not covered with chaffy scales. A Pappus (modified outer perianth series of Asteraceae is borne on the ovary and it may be bristle, plume, scale or awn like) is present. Here it has 1-2 rows of rough bristles. The Male florets are in heads of up to 14 individuals. Male tree flowering is displays up to 31 attractive yellow coloured florets are visible when pollen covers the flower heads in spring. The Corollas are a dull yellow. The ovary is abortive. In the Female florets, there are heads of up to 27 individuals. The Corolla is 5 lobed, filiform (thread or filament like) and is also dull yellow. Staminodes (sterile stamens) are absent. There is a single Pistil (a unit of the Gynoecium, the female element of the flower, composed of the Ovary, Style and Stigma). The inferior Ovary has an exserted (sticking out; projecting beyond the perianth) Style. (Aug-Sep).
The Fruit is a cypsela (Asteraceae – a dry single-seeded fruit formed from a double ovary of which only one develops into a seed), which has an apical tuft of orangey bristles. It is about 5mm long. The long, bristle tipped Seeds are small and light. (Aug–Dec).
Distribution & Ecology
This Tree is common on rocky ridges, koppies and hills. It is also found in inland forests and wooded grasslands. Located in the Free State, Gauteng (Johannesburg, Pretoria, and Magaliesberg), Mpumalanga, Limpopo, North West, Botswana, southern Mozambique, Zimbabwe and Zambia. It is often associated with Englerophytum magalismontanum (stamvrug).
The Tree is hardy, fast growing and transplants well. The creamy-brown Wood is strong but not very straight, nor of a useful size.
Burrows, J.E., Burrows, S.M., Lotter, M.C. & Schmidt, E. 2018. Trees and Shrubs Mozambique. Publishing Print Matters (Pty) Ltd. Noordhoek, Cape Town. 2018.
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.