Gardeners need not hesitate on the choice of tree if the keurboom
is on the list; it is a beautiful tree, suitable for both the domestic
garden and big landscapes. It is fast-growing, beautiful in flower
and has an attractive growth form.
divaricata and V. oroboides are very similar and are
often confused with each other. Both are small to medium-sized trees,
with a bushy, rounded to broadly conical growth habit with branches
growing close to the ground.They are very fast-growing when young,
attaining up to 1.3 m. in a year, and reaching their full height
in only a few years. V. divaricata rarely exceeds 10 m in
height; V. oroboides can reach up to 15 m. They are also
relatively short-lived, their average lifespan being 12 to 20 years.
The bark is silver-grey and smooth in young trees; as the tree gets
older the bark turns grey and rough. The trunk can grow up to 600
mm in diameter.
leaves are pinnately compound in both species. V. divaricata
has 5-9 pairs of leaflets plus a terminal one, whereas V. oroboides
has 6-12 pairs of leaflets plus the terminal leaflet.
leaflets have entire margins and the stipules fall early. V.
oroboides leaflets are smaller and greyish green in colour and
are densely covered in velvety hairs, whereas those of V. divaricata
are green and almost hairless.
The keurboom has beautiful, sweetly scented, pea-shaped
flowers in dense terminal sprays about 100 mm long. V. divaricata
has pinkish mauve to violet-pink flowers and the keel has dark purple
tips. The flowers are produced in profusion in spring to early summer
(August to November). V. oroboides flowers are pale pink
or pinky-white to white and they are produced in profusion in mid
to late summer (January to April).
to add to the confusion, the V. oroboides trees near George
have rose-violet or purple-violet flowers during spring, but can
be differentiated from V. divaricata by the conspicuous rust-coloured
hairs that cover the leaves and twigs. Both species flower sporadically
out of season. Both produce a flat, brown, velvety 50-80 mm long
pod, becoming black with age, which splits into 2 valves releasing
2 - 6 seeds.
The keurboom is native to a small, narrow strip along the southeastern
coast of South Africa. Virgilia oroboides is found below
1 200 m in a narrow strip along the coast from the Cape Peninsula
to George. V. divaricata also occurs below 1 200 m but from
Klein Swartberg Mountains to George to Van Staden's Pass near Port
Elizabeth in Eastern Cape. Both occur in forest margins, most often
beside streams or on river banks but also on hillsides and thickets.
V. divaricata is found in abundance in the Knysna and Plettenberg
Bay area, particularly along the Keurbooms River, which takes its
name from this tree.
flowers of both species are rich in nectar and attract many insects
and birds, such as sunbirds, carpenter bees, honey bees and ants.
Also, many birds such as doves and white-eyes nest in them. In the
forest, the large handsome ghost moth, Leto venus, lays its
eggs at the foot of the keurboom so that the hatching caterpillars
can bore into the wood. The blue butterfly, known as the Lucerne
Blue, Lampides boeticus, breeds on lucerne and on keurboom
Derivation of the name and historical aspects
These two species have a rather complicated history of naming. Virgilia
oroboides has quite a few synonyms and both have been called
V. capensis although by different authors. There is still
an argument about whether they are one variable species or two separate
species. At present they are regarded as two separate species, and
V. oroboides is divided into two subspecies; the rose-violet-flowered
plant with rust-coloured hairs on the leaves and twigs that occurs
near George being V. oroboides subsp. ferruginea and
the pale, pink-flowered plant with white hairs on the leaves and
twigs that occurs from the Cape Peninsula to Swellendam being V.
oroboides subsp. oroboides.
The generic name Virgilia was given in honour of Virgil,
the greatest of Roman poets. The specific epithet oroboides
means resembling Oribus, a genus of plants with pea flowers
that is now included in Lathyrus, the sweet pea genus; ferruginea
means of the colour of iron-rust and refers to the rust-coloured
hairs that cover the leaves and twigs of this subspecies; divaricata
means divergent and refers to the widely spreading branches. The
Afrikaans common name was inspired by the beauty of these trees,
and means 'the pick of all trees' (keur meaning choice and
boom, a tree, pronounced to sound like cure bwoom). Keurboom
trees were cultivated in England as long ago as 1767 and are grown
in Australia and in the USA today where they are also known as tree-in-a-hurry
or Cape lilac.
In earlier times the wood was much in demand for yokes. It was also
used for spars, wagon-bed planks and rafters, and can be used for
furniture. The transparent gum that exudes from the bark was once
used as a substitute for starch.
Growing V. oroboides and V. divaricata
attractive fragrant flowers and the fast growth rate make the keurboom
a popular tree for the garden. Of the two, Virgilia divaricata
is the better choice as its foliage is more luxuriant, and its growth
more compact and it is amazingly beautiful when in full flower.
A keurboom is the perfect tree for the new, bare garden because
it grows so fast it will take only two or three years before it
will be creating shade, or a screen, and filtering the wind - which
is an important consideration in Cape Town suburbs. It is also one
of the best species to use as a pioneer in the first stage in the
succession to forest. It is happy to grow out in the open, grows
fast and quickly and creates the shade that the slower-growing,
more permanent trees need to grow in.
Virgilia is propagated from seed. The seed coat is hard and requires
some stimulation to initiate germination. Seeds can be soaked in
hot water before sowing, or the seed coat can be cracked artificially.
They also respond to stimulation by fire and can be treated with
Instant Smoke Plus Seed Primer. Seed should be sown in autumn
or spring, in well-drained soil at a depth of 0.5 - 1 cm and covered
with the sowing medium or milled bark and then watered. Seed can
also be sown in situ, e.g. for forest rehabilitation projects. The
seeds are highly fertile and can remain alive for many years after
they have fallen, even after as many as 30 years they will germinate
if conditions are favourable.
the seedlings after the first pair of true leaves has emerged when
they are large enough to handle. Virgilia seedlings grow fast and
can be planted into pots or bags for growing on, or directly into
their permanent position in the garden. Feed moderately with a liquid
fertilizer and water generously. Plant the young trees into a permanent
location in full sun or semi-shade. They need good, light soil and
plenty of water, particularly during their first 2 to 6 years. Virgilias
have strongly spreading surface roots and are greedy feeders; they
will benefit from frequent generous applications of compost or organic
mulch. Virgilias are sensitive to frost, particularly when young.
Mature trees may withstand short periods of frost, but not prolonged
exposure to freezing temperatures.
- Coates Palgrave, M. 2002. Keith Coates Palgrave Trees
of southern Africa, edn 3. Struik, Cape Town.
- Goldblatt, P. & Manning, J. 2000. Cape plants.
A conspectus of the Cape flora of South Africa. National Botanical
Institute, Pretoria & Missouri Botanical Garden.
- Palmer, E. & Pitman, J. 1972. Trees of southern
Africa. Balkema, Cape Town.
- Phillips, E.P. 1928. Virgilia capensis. The Flowering
Plants of South Africa 8: t. 305.
- Smith, C.A. 1966. Common names of South African plants.
Memoirs of the Botanical Survey of South Africa No. 35.
- Van Wyk, B. & Van Wyk, P. 1997. Field guide to
trees of southern Africa. Struik, Cape Town.
Author: Giles Mbambezeli & Alice Notten
Kirstenbosch National Botanical Garden