This shrub or small tree, with its lobed discolorous leaves, large sharp prickles and large poisonous yellow fruit, has long been used as a hedge plant.

Description
This much-branched shrub or small tree is 1-5 m high, usually heavily armed with large, sharp, brown, straight to recurved, broad-based and laterally compressed prickles up to 15 mm long. Young branches are covered with a grey or pale brown tomentum, becoming glabrous and dark brown with age. Leaves are shortly petiolate, ovate, up to 150 × 130 mm, usually deeply 5-7-lobed, with the upper surface green glabrescent, the lower surface thickly stellately whitish tomentose, more or less prickly on the midrib on both surfaces. The inflorescence is a few to 10-flowered racemose cyme with only the proximal flowers female-fertile. The calyx is enlarged and prickly in fruit. The corolla is white to pale violet, rotate-stellate, about 20 mm in diameter. The fruit is a smooth, globose berry, often with a warty surface, up to 60 mm in diameter, green ripening to yellow. Seeds 4 × 3 mm in size. Chromosome number: 2n = 24.

The lobed discolorous leaves, the mostly recurved prickles and the large yellow fruit make this plant unique among the African species of Solanum. It could perhaps be confused with S. lichtensteinii (= S. incanum in the broad sense ), but that small shrub is unarmed or has small prickles.
The flowering time is from September to July, peaking in November and March. The fruiting time is from April to January, peaking in June and November.

Distribution and habitat
S. aculeastrum subsp. aculeastrum occurs from tropical Africa down to South Africa. There are two other subspecies that are restricted to East Africa. In southern Africa this taxon is found in Limpopo, Mpumalanga, KwaZulu-Natal, Western and Eastern Cape and also in Swaziland.
S. aculeastrum subsp. aculeastrum occurs naturally in grassland, woodland and in forest margins, but also in disturbed places. In southern Africa it prefers a high rainfall of more than 700 mm per year and it is found from 275-1 780 m altitude. It has been recorded from gentle to steep slopes and on all aspects, on various soil types e.g. sandy soils, reddish brown clay-loam and brown sandy loam.
Acocks (1988) regards this species as an undesirable plant which should be reduced in number by appropriate veld management. It is listed as a component of the North-eastern Mountain Sourveld.

Derivation of the name
As discussed under S. giganteum, Jaeger (1985) explains that the genus name Solanum is possibly connected to the Latin noun solamen, meaning a relief or comfort, assumed from the palliative effects of the nightshades. The species name aculeastrum refers to the sharp-pointed prickles on most parts of this plant.
The Solanaceae is an economically important family of about 2 600 species of plants, with its chief centre of diversity in Central and South America. This family contains many poisonous, medicinal and edible plants, and also several horticultural favourites as well as many weeds. Solanum is a large, cosmopolitan genus of perhaps as many as 1 500 species; about 50 of these species are found in southern Africa and about 30 of them are indigenous.
S. aculeastrum belongs to the section Melongena of the subgenus Leptostemonum. Species of this section are found in Africa and Asia; one of which is the cultivated S. melongena (egg-fruit, aubergine, brinjal) which was probably domesticated in China, and which today is an important vegetable, particularly in the Mediterranean and Asia, belongs here. About seven species of this section occur naturally in Africa and they all have white to violet flowers and yellow, fleshy fruits. S. aculeastrum appears on the official Tree List of South Africa (no. 669.3) and of Zimbabwe (no. 1013).

Uses and cultural aspects
In rural areas the goat bitter-apple is in common use as a hedge or as living fencing material for retaining livestock. It is sometimes used as a windbreak. It is well suited for these purposes because of its fast growth, its eventual size and in particular its large, hooked prickles. As a result it is often found growing in thickets close to human dwellings. The fruit is sometimes used as a soap substitute; apparently it has a high saponin content.
According to Hutchings et al. (1996), the extremely bitter fruit of S. aculeastrum is used medicinally (fresh, boiled or burnt) in various ways for humans as well as domestic animals. The fruits, both mature and immature, contain the poisonous alkaloid solanine.

Growing Solanum aculeastrum

This plant could be an attractive garden subject, but unfortunately no information can be found. It is clear that it can be grown fairly easily in high rainfall areas and that it can tolerate some frost. It can probably be propagated by truncheons and from seed.

References.

• Acocks, J.P.H. 1988. Veld types of South Africa, edn 3. Memoirs of the Botanical Survey of South Africa No. 57. Botanical Research Institute, Pretoria.
• Dold, A.P. & Cocks, M.L. 1999. Preliminary list of Xhosa plant names from Eastern Cape, South Africa. Bothalia 29: 267-292.
• Hutchings, A., Scott, A.H., Lewis, G. & Cunningham, A.B. 1996. Zulu medicinal plants, an inventory. University of Natal Press, Pietermaritzburg.
• Jaeger, P.-M.L. 1985. Systematic studies in the genus Solanum in Africa: 1-540. Ph.D. thesis, University of Birmingham. Unpublished.
• Van Wyk, B. & Van Wyk, P. 1997. Field guide to trees of southern Africa. Struik, Cape Town.
• Von Breitenbach, F. 1981. Standard names of trees in southern Africa, Part II: Venda tree names. Journal of Dendrology 1,3 & 4: 84-94.
• Von Breitenbach, F. 1991. Standard names of trees in southern Africa, Part VII: Setswana tree names. Journal of Dendrology 13: 29-35.
• Von Breitenbach, J., De Winter, B., Poynton, R., Van den Berg, E., Van Wyk, B. & Van Wyk, E. 2001. Pocket list of southern African indigenous trees: including selected shrubs and woody climbers, 1st abridged impression of edn 4. Briza Publications & Dendrological Foundation, Pretoria.
• Watt, J.M. & Breyer-Brandwijk, M.G. 1962. Medicinal and poisonous plants of southern and eastern Africa, edn 2. Livingstone, Edinburgh & London.