Bolusanthus speciosus

Description

One of our most splendid indigenous trees, with dark, beautifully corrugated bark, a tall, graceful form and a narrow, ascending, often weeping crown of silvery grey-green leaves that shimmer in the sunlight. In spring, the tree is truly a fine sight, when it produces large, pendant sprays of striking, bluish mauve, wisteria-like flowers. It is a protected tree in South Africa.

SA Tree

Family

This family is also divided into 3 subfamilies; mimosa or acacia subfamily, cassia and pea.
Regarded as one of the largest, as well as economically significant families, its members have been cultivated since early times for their plethora of uses – as food, medicine, fodder, for practical use (tannins) and ornamental displays.

Habitat

Usually found in low to medium altitudes, in a variety of soil types, but typically an indicator of clay soils.
The trees are naturally prevalent in open and wooded grasslands of South Africa, also bushveld, and are often found growing on heavy, alkaline soils.
From Angola and Malawi, to the warm northern parts of Natal, also Zimbabwe and the northern and eastern parts of Gauteng.
The largest specimens are generally found on heavy soils near water.

Bark

Pale, grey-brown and glabrous on younger trees, maturing to a dark grey-black, and becoming increasingly rough and heavily furrowed or corrugated.
The main stem is usually quite straight, but can be multi-stemmed, and branchlets eventually scale into parts, leaving behind dark brown lenticels.

Foliage

Briefly deciduous, losing its leaves only for a short period in late winter or early spring.
The leaves are compound, (200-300 mm long), with 3-6 pairs of leaflets, plus a terminal, unpaired one, and oppositely or spirally arranged.
Lanceolate to narrowly elliptic (60-70 x 10 mm), with faintly curled tips, and smooth or slightly, erratically scalloped margins.
They are glossy, bright green to grey-green above, and paler below, with a conspicuous yellow midrib and pale-yellow lateral veins.
Older leaves are smoother, while the young leaves are covered by fine, silvery- bronze hairs.

Flowers

Strikingly beautiful, pendant sprays (250-300 mm), of numerous, pea-like, pale blue to violet or mauve flowers.
Each bell-shaped flower has five unequally shaped petals and five lobes, and a white “flare” can be seen in the centre of the upper petal.
Silky textured, almost stalkless, with a very insignificant scent, and produced before or with new leaves.
August – March.

Fruit

Hanging clusters of flat, narrow and sharply pointed pods (70-100 x 10 mm), with a papery texture.
They have a light brown hue when young and ripen to a dark grey-brown or black.
The pods can remain on the tree for a long time but remain closed.
February – April)

Height

Spread

Medicinal

The roots and bark, less often the leaves are used.
Several Flavonoids, with antimicrobial and antioxidant properties, have been isolated from the root and stem bark.
The inner bark is dried and pulverized, then used to treat abdominal disorders and cramps, and concoctions made from the boiled roots are also taken orally or as emetics to alleviate stomach ailments.
In certain areas, a leaf infusion is taken to stop vomiting.

Practical

The whitish-yellow to grey-brown wood is hard, heavy, durable and works well.
The straight growing stems are very solid, termite and borer resistant and apparently do not burn easily, making them highly valued for fencing poles and smaller implements.
The timber also makes high quality furniture, and is widely used in the construction of tools, handles and other articles.

Wildlife

The flowers will attract butterflies, honey and Carpenter bees, as well as a host of other insect life, and the new flower buds are often eaten by monkeys.
The leaves and pods are eaten by game animals (giraffe, elephant, large and small antelope), as well as livestock.

Advantages

These trees have very high potential as garden ornamentals, and are highly decorative, especially when in flower.
They make good shade trees, and because they do not have aggressive root systems, they are ideal specimens for beautifying smaller and townhouse gardens, as well as patios, as they do well in large containers.
For bee keepers, they are an excellent choice, as the flowers are a rich source of nectar.
Bolusanthus s. looks splendid when planted as part of a mixed border and is one of the best trees for street and avenue planting.
The tree is an indicator of underground water on farmland.
Very popular as a bonsai subject.
The trees have a symbiotic relationship with certain soil bacteria, which form nodules on the roots and fix atmospheric nitrogen.
Some of this vital nitrogen is used by the growing plant and can also be used by other plants growing nearby and will benefit development.

Tolerance

The trees prefer areas with hot summers and low rainfall, and, once properly established, can endure mild but not severe or extended frosts.
They can withstand a fair amount of drought once established but should be watered well and frequently for at least the first 4 years to promote sturdy and healthy growth.

Growth Rate

If planted in a sunny, warm position with good quality soil, it can be fast growing, between 600 & 800 mm per year.
The growth will be rapid when the tree is young, but generally slows down as it ages.
First flowering can be expected at 6-7 years of age, if grown from seed.

Lighting

Soil & Water

Prefers a very well-drained, sandy or loamy, slightly alkaline soil, but will tolerate clayish soils.
Added compost will always benefit the tree, and during very hot periods, an added layer of mulch around the tree will help retain moisture.
Water-wise, the species prefers a hot dry climate.

Propagation

Soak the seeds for 8-12 hours in lukewarm water to aid germination. Sow in a mixture of river sand and compost (2:1), and cover with a fine layer of sand.
Place the trays in a warm, bright area and mist often.
Germination is usually fair and rapid, within 4-5 weeks.