One of the icons of the South African veld, Vachellia karroo, the Sweet Thorn, is a very spectacular tree when in full flower.

Vachellia karroo, the Sweet Thorn, is, in cultivation, a medium to large single stemmed, deciduous tree. With a rounded crown that is often wider than it is tall. An icon of the South African veld, Vachellia karroo is a popular choice among local gardeners as a pavement tree or as a shade tree in larger gardens. It is a  very spectacular tree when in full flower.

Family:                       FABACEAE             (Pea family)

Sub-family:               MIMOSOIDEAE   (Thorn tree sub-family)

Name Derivation:

  • Vachellia  – named in honor of Rev George Harvey Vachell (1799-1839), who collected plants in China while the chaplain to the British East India Company in Macao.
  • karroo – from the Karoo. The name, Karoo, was incorrectly spelt when the species was first described and cannot be corrected.

Common Names:           Sweet Thorn (Eng), soetdoring (Afr), mooka (Nso & Tsw), leoka (Sso), singa (Tso), muunga (Ven), umnga (Xho)and umunga (Zul)

SAF Number:                  172                         Z Number:            189

Form:                                

  • In cultivation a tree with rounded crown around 7m, but can reach 12m.
  • In the wild it is often shrubby and invasive.

Size:                                   5 – 7m by 5 – 7m, may even reach 12 m

Flower:

  • Bright yellow, round ball- like flowers, to 1.5 cm diameter.
  • In clusters at the ends of branchlets.
  • Free flowering and spectacular in full flower.
Vachelia karroo flowers are on a round, ball-like inflorescence, bright yellow and fragrant.
Colour                                 Bright golden-yellow.

Flowering Months:         Nov – Feb (or even till Apr).

Fragrance:                         Flowers are sweetly scented.

Foliage:

  • Deciduous.
  • Leaves are bipinnate and feathery.
  • They are arranged alternately on the branches.
  • Leaves are dark green.

A Vachellia karroo in full flower is a wonderful spectacle.

The leaves of Vachellia karroo are bipinnately compound.
Thorns:

  • Straight, prominent white thorns are paired.
  • Thorns grow from the base of the nodes.
  • Older branches have fewer and less developed thorns.

Fruit:

  • The pale brown, sickle-shaped pods have some constriction between seeds.
  • Pods remain on the tree for quite a long time.
Bark:

  • The old bark is rough and fissured, dark brown to black.
  • Young bark reddish brown with whitish to beige lenticels. 

In the Garden:

  • Suitable for larger gardens and large pavements as a shade tree, wind break, screening or feature tree.
  • Because it is both extremely water-wise and cold resistant, it can be grown in areas where these factors limit choice of trees.
  • A very good choice for larger wildlife friendly gardens, attracting insects, butterflies and birds.
  • Good and popular bonsai subjects.

Soil Needs:

  • Grows naturally in many different soil types, added nutrition will reward the gardener.

 Care:

  • A low maintenance garden tree.
  • Plant in a cubic metre hole with lots of compost and some bonemeal can produce growth of  a 1 m and more per year.
  • May be pruned to shape.

Cold Hardiness:                  Very cold hardy.

The paired thorns are straight, white with a dark tip and may be up to 10 cm long.

The Vachellia karroo seed pods are quite long (up to 15 cm), narrow and sickle-shaped.

Vachellia karroo is a handsome tree with a beautiful, rounded crown. The canopy is a favorite nesting site for many birds.
Water Requirements:

  • Very drought hardy.
  • Water-wise.            

Light Requirements:     Full sun.

Roots:       Aggressive roots, do not plant too near paving, swimming pools, walls or buildings.

Birds:

  • Used by insectivorous birds for foraging and gleaning.
  • Flowers and seeds are eaten by many birds (for a number of years a family of Brown-headed parrots visited the old nursery in Broadacres to feed on ripe Vachellia karroo and Combretum erythophylum seeds when they were ripe!).
  • Thorny branches are favoured nesting sites of many garden birds.
Insects and Butterflies:

  • Bees are attracted to the flowers.
  • In gauteng, a larval host to Thorn-tree blue, Velvet-spotted blue, Topaz-spotted blue, Black heart, Common Hairtail, Mashuna hairtail, Talbot’s hairtail, Black-striped hairtail, Eastern scarlet, Club-tailed charaxes
  • Elsewhere possibly larval host to Mirza blue, Natal spotted blue, Little hairtail, Otacilia hairtail, Dark-banded scarlet, Purple gem and Brilliant Gem.

Medicinal:

  • An old Cape recipe of bark and leaves are used to treat dysentery and diarrhoea, the presence of acaatechin, quercetin and catechutannic acid suggest it will be effective.
  • The gum, bark and leaves are used to treat colds, hemorrhaging and conjunctivitis.
  • Gum is used to treat oral thrush.
The delightful Eastern Scarlet (Axiocerses tjoane tjoane) larvae feed on the leaves of Vachellia karroo and other Vachellia and possibly Senegallia species

The edible gum is sweet and often eaten by children.

A Vachellia karroo, Sweet Thorn, growing in the Karoo on the plateau in the Mountain Zebra National Park.

Poisonous:                       Not poisonous.

Notes of interest:

  • Flowers, pods and leaves eaten by stock and game.
  • The bark of younger branches is used to tan leather, giving the end product a reddish colour.
  • The flowers provide nectar and pollen that make the trees popular with apiarists.
  • The gum is edible and often eaten as sweets by children, and is used in confectionary and pharmaceutical production.
  • Powdered root mixed with animal fat is used by some peoples in Nam to dress hair.
  • Seeds roasted and ground have been used as a coffee substitute.

Natural Distribution:

  • WC, NC, a broad strip from south to north of Nam, eastern and north-western Bot, EC, KZN midlands, FS, NW,G, L, western M and south-west and central Zim.
  • Northwards into Ang, Zam and Mal.

Natural Habitat:

  • Grasslands, fynbos, succulent-Karoo, Nama-Karoo, thickets, savanna-bushveld, savanna-woodland, savanna-Kalahari and savanna-lowveld.

Links to other members of the MIMOSOIDEAE   (Thorn tree sub-family)

 

To go to the “plant blog” click on the plant name below the picture.

© Malcolm Dee Hepplewhite & Witkoppen Wildflower Nursery, (Text and Photographs) 2011 & 2018.