General Info

This Tree may reach 7m+ high. Single, short, straight, spines are on the trunk. The Leaves are imparipinnate. The unisexual, 4-merous Flowers in panicles. Fruit – capsule with shiny Seeds.



Zanthoxylum capense, Fagara capense, Fagara magalismontana, Zanthoxylum thunbergii.

RSA Tree No. 253.

Common names: Small knobwood, Lemon thorn, Fever Tree, Knobwood, Adelade Spice Tree, White man’s Tit.

Family: Rutaceae (Citrus family) has 160 genera and 2 000+ species. Leaves often have pellucid (clear, almost transparent in transmitted light) oil glands which are responsible for the aromatic smell. These gland dotted leaves are usually opposite but lack stipules. The regular Flowers are bractless, bisexual or unisexual and usually monoecious. They have 4-5 Petals, which are usually free. The Stamens have anthers that are dorsifixed and 2-thecous (have 2 pollen sacs). Staminodes are often present. The Ovary usually has 5 carpels and the style is simple. Fruit is variable. This family has 23 species in Africa. The Rutaceae in southern Africa are largely concentrated in the Western Cape. Indigenous genera with trees include Calodendron, Ptaeroxylon, Vepris and Zanthoxylum.

Name derivation: Zanthoxylum – yellow wood. capensis – from the Cape. There are 6 species of the genus Zanthoxylum in southern Africa.

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

This Tree is usually much branched and up to 7m but may reach 15m high. It has a sparse Crown. On young grey branches, straight – initially orange then dark brown and hard Spines are present. These spines are single, short, straight, light brown and are seated on randomly placed cone-shaped knobs. They may be in pairs. Initially the Bark is smooth. With age, the grey bark becomes brown.


The imparipinnate (pinnately compound leaf ending in a single leaflet) Leaves are up to 12cm long. However, the terminal leaflet may be missing. These eaves have a citrus smell when crushed.  Leaves are concentrated near branch ends. The Rachis (main axis bearing flowers or leaflets) is grooved and thinly winged on top (photo 112). Straight Spines up to 1cm long may be present (photo 115). Leaflets are sessile and tend to increase in size towards the apex. Leaflet shape varies from almost round to elliptical and the largest terminal single leaf may be obovate. Up to 8 almost pairs of leaflets may be present. The Margin is scalloped to shallowly serrate (saw-toothed margin with teeth pointing forward). Translucent Gland Dots are visible only on the margin at the axis of the serrations. The lower side of the Blade is slightly lighter and here the midrib and lateral veins are a little more visible. On the upper surface, the midrib is visible. The asymmetric Base tapers, and has small auricles (resembling an ear or earlobe) adjacent to the petiole (photo 109 RHS). Holding the leaf against a strong light enables the veins and translucent dots along the margin to be seen (photo 123). Here a hand lens will help. The Apex varies from obtuse to rounded. The Petiole (leaf stalk) is about 1,5cm long. Petiolules (base of leaflets) are very short. Stipules (basal appendages of the petiole) are absent.


The greenish white to pale yellow sweet smelling Flowers are small. They are located in short, branched terminal Panicles (indeterminate, branched inflorescence with stalked flowers) which may be somewhat upright. They have a short Pedicel (stalk of a single flower in a cluster). Flowers are unisexual and may be monoecious (having both male and female reproductive organs on the same plant) or dioecious (having male and female parts on separate plants). When monoecious, both male and female flowers may occur in the same panicle. They are actinomorphic (regular, symmetrical. Perianth, the calyx and corolla, can be divided into 3 or more identical sectors). The Calyx has 4 small ciliate (hair-like) Sepals. There are 4 free Petals in the Corolla. The Male Flowers have 4 Stamens which are opposite the sepals. A rudimentary ovary is present. In the Female Flowers there are 4 Staminodes (sterile stamens) which are inserted at the base of a gynophore (a stalk present in some flowers that supports and may elevate the gynoecium). The glabrous (hairless) superior Ovary is conspicuously gland-dotted and has 2 distinct seams. The single Locule (chamber within an ovary) has 2 Ovules and the short simple Style has a capitate (formed like a head) Stigma. (Aug-Feb).


The small green Fruit becomes red, glandular and almost spherical Capsule (a dry fruit resulting from the maturing of a compound ovary, which usually opens at maturity by one or more lines of dehiscence) with a persistent Calyx. It is up to 5mm wide. Fruits open to expose shiny, black, oil-rich Seeds. The fruit is also citrus scented. (Feb-May).

Distribution & Ecology

This Tree occurs from about Knysna in the Western Cape, eastwards to Eastern Cape, Kwa-Zulu Natal, Swaziland, Mpumalanga, Mozambique and Zimbabwe. In terms of the National Forests Act no. 84 of 1998 this is a protected tree in South Africa. It is found in rocky slopes, rock outcrops, in dry areas and mist belts from sea level to about 2 000m. Butterfly larvae that feed on the Leaves include the citrus swallowtail (Papilio demodocus), the white-banded swallowtail (Papilio echeroides) and the emperor swallowtail (Papilio ophidicephalus). Among the Antelope that browse the leaves are the grey duiker, the kudu and the klipspringer. Birds are attracted by, and consume the Seeds. Monkeys disperse seeds. A sap sucking insect Trioza erytreae can cause problems with this and other Rutaceae species. Monkeys and baboons eat the ripe Fruits.


The Wood is quite hard and yellowish. The Fruit is reported to leave a persistent burning sensation in the mouth. The Bark is sold on local markets for medicinal use.  The stem bark and Leaf extracts have shown moderate resistance to some bacteria and fungi. Extracts have shown to have insecticidal activity. The easiest way to Grow this plant is to gather seedlings from under the tree. Fresh seeds can be planted but these do not germinate easily.


Boon, R. 2010. Pooley’s Trees of eastern South Africa. Flora and Fauna Publications Trust, Durban.

Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of Southern Africa, edn 3. Struik, Cape Town.

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.

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