General Info – summary

This Tree is up to 8m high and trunk is up to 20cm wide.  Bark becomes dark and deeply grooved.  Alternate Leaves are simple.  Dioecious trees are capitula with the small yellow Florets (flowers) contained within a panicle.  Male florets with 5 anthers, female florets with one pistil, inferior ovary and an exserted style. The Fruit is a cypsela.  Pappus has an apical tuft of bristles for the wind dispersal of seeds.

Description

Brachylaena rotundata

Previous Names: Brachylaena discolour var. rotundata, Brachylaena rhodesiana.

SA Tree No. 730.

Common names: (Afr) Bosvaalbos, Bergvaalboom.  (Eng) Highveld Silver-oak, Mountain Silver Oak, Mountain Silver-oak, Yellow Silver-oak.

Family Asteraceae, Compositae.  (Daisy family: includes sunflowers, lettuce, chicory, marigolds and Brachylaena).  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 on this website 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 in the Asteraceae are called Florets that usually have a base of 5 fused Petals.  The Sepals are replaced by a Pappus (the modified calyx, the part of an individual floret, that surrounds the base of the corolla tube in flower heads of the plant family Asteraceae.  The pappus may be bristle, plume, scale or awn like.  In all members, the central florets are called Disc Florets.  In some members, excluding Brachylaena, the outer florets (Ray Florets) are also present.  These occur around the periphery of the flower.  Ray florets are usually long and brightly coloured (like the yellow outer florets in the sunflower).  Four or 5 stamens are fused to the corolla.  An inferior Ovary is present containing 1 Ovule and the Style has 2 lobes.  Each floret produces 1 Fruit with 1 Seed.

Name derivation: Brachylaena – short cloak – referring to the short floral bracts.  rotundata – with roundish leaves.  Ray florets are absent in the genus Brachylaena.

Conservation: National Status: L C. (Least Concern).  Assessed: Raimondo et al. (2009).

Tree

This Tree may reach 8m high or it may develop as an untidy much-branched shrub.  The Trunk has a diameter of up to 20cm.  The plant is usually solitary or may develop in small groups and the often-low-down Branches (photo 506) tend to droop.  The Bark is dark, blackish or brown-grey and ages to become deeply grooved (photo 896).  The usually slender smooth Twigs (1-year-old current branch segments) are initially covered with white hairs (photo 489) but slowly become purplish or reddish-brown and hairless.  Here Leaf Scars are clearly visible.  Young stems have the pale, raised Lenticels (a usually raised corky oval or elongated area on the plant that allows the uncontrolled interchange of gases with the environment – (photo 180).  In this photo they run lengthwise.

Leaves

The alternate and leathery, Leaves (photo 239) are narrowly elliptic/oblong-elliptic, ovate, oblanceolate (upside down egg) or oblong and up to 2-10 x 2,5-6cm (photo 597).  They are larger on coppice shoots (thicket or grove of small trees or shrubs, especially one exposed to periodic burning, cutting or pruning).  The tree may be deciduous – mainly temperature dependant.  The Upper surface is white on younger leaves (photo 236) and on mature leaves it becomes almost glabrous (hairless) and a dark green colour (photo 236).  Soft hairs cover the much lighter Lower surface (photo 597).  Here the protruding Midrib and the lateral Veins are clearly visible.  The veins may form a loose Y before reaching the margin (photo 569 & 897).  Slightly red autumn colours may develop.  The bluntly pointed 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 variable Margin is often entire or roughly and irregularly toothed – especially away from the base (photo 569).  The short, slightly swollen Petiole (leaf stalk) is up to 7mm long (photo 597).

Flowers

Flowers develop in Synflorescences (compound inflorescences).  Here, in axils (the upper angle between the petiole and the stem) of fallen leaves, they become arranged in Panicles (indeterminately, branched inflorescence with stalked flowers (photo 653).  Within the synflorescence, each smaller inflorescence is a Capitulum (a false flower containing a dense cluster of many small, drab yellow Florets (individual Flowers mainly in Asteraceae and grasses).  These yellow Florets may precede the new leaves.  Individual florets have Sepals replaced by a bristle like Pappus (the modified calyx, the part of an individual floret that surrounds the base of the corolla tube in flower heads of the plant family Asteraceae).  In the Corolla each floret usually has 5 fused Petals.  Below and outside the sepals and petals are 5-8 whorls of small overlapping Bracts (usually much-reduced specialised leaves – photos 40 & 45 – under Fruit).  Photo 40 show the bracts that remain after seed dispersal and loss of florets.  The capitula collectively form in a panicle that is between 4 and 40cm long.  They may be shorter when occurring in axils of fallen leaves.  Each capitulum (photo 654) is about 1cm long and supported by a single Peduncle (stalk of the flower cluster – photo 45 under Fruit).  A single, short Pedicel (stalk of a single floret) supports each Floret. The Involucre (whorls of visible, initially green bracts) are in 5-8 rows.  In photo 45 – under Fruit, the now clearly noticeable old bracts have aged from green to brown.  These are similar to a shaving brush when completely open (photo 653).  The Corolla has a dull tube ending with 5 recurved, light yellow petal lobes.

This plant 1s dioecious (unisexual floral structures with functional male and female parts on separate plants).  In spring the male tree produces the most attractive golden yellow pollen covered flowers.  In each Male Capitulum a dense cluster of 13 to 31 florets develops.  Here the 5 Stamens are attached to the non-functional style and surround the non-functional Stigma.  The Anthers are introrse (the line of dehiscence faces towards the flower centre).  Individual male florets/flowers have an abortive Ovary.  In the Female Capitula 11-27 florets develop.  Present 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 a single ovule, and the Style is exserted (sticking out) beyond the perianth (the 2 floral envelopes considered together; a collective term for the calyx and corolla) and ends with a Stigma (the part of the pistil that receives the pollen.  (Aug-Sep).

Fruit

The Fruit is a cypsela (a dry single-seeded fruit formed from a double ovary of which only one develops into a seed), tipped with creamy bristly hairs.  In the photos below the remains of the whorls of small overlapping Bracts are visible.  Aug ++

Distribution & Ecology

This plant is an Endemic (restricted to a particular geographic location) in southern Africa.  It is common on rocky ridges, hills and occurs in open woodland, and bushveld and on koppies (a small, natural, often rocky and slightly isolated, natural hill slightly above the flattish African veld).  The plant may be associated with termite mounds and often grows with Englerophytum magalismontanum (stamvrug) and Mimusops zeyheri (moepel).  It is also found in inland forests and wooded grasslands.  In South Africa these plants are located in the Free State, Gauteng (e.g., Johannesburg at Melville Koppies Nature reserve, Pretoria, and Magaliesberg), Mpumalanga, Limpopo, North West.  Beyond South Africa these plants occur in Botswana, Mozambique, Zimbabwe and Zambia.  This plant is absent in Namibia.  Flowers attract bees and flies – the agents of pollination.

Ethnobotany

The Tree is hardy, fast growing and transplants well.  The creamy-brown Wood is strong and sought after for tools, axe handles and carving, but beyond this, it is not large enough to be of a useful size.  (It has similar properties to those of the Ash – Fraxinus sp. in family Oleaceae).  Ash trees occur naturally in Europe, Asia and North America.

References

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.

Foden, W. & Potter, L. 2005. Brachylaena rotundata S.Moore. National Assessment: Red List of South African Plants version . Accessed on 2024/10/26.

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. Jacana, Johannesburg.

van Wyk, B. & van Wyk, P. 1997 Field guide to Trees of Southern Africa. Struik, Cape Town.

 

http://www.greenplanet.co.za/plant/Brachylaena-rotundata

https://en.wikipedia.org/wiki/Brachylaena_rotundata

http://www.mk.org.za/mkflora.htm

file:///C:/Users/Probook/Downloads/800-1861-1-SM.pdf

http://posa.sanbi.org/flora/browse.php?src=SP