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Small Knobwood

Zanthoxylum capense

SA tree no: 253

English: Small Knobwood, Knobwood, Pepper-bark, Perdepram

Afrikaans: Kleinperdepram, Perdepram, Knoppiesdoring

Xhosa: Umkhukhuma, Umngqale, Umnungwane

Zulu: Umungamungu, Ulwazimfudu

N. Sotho: Monokana-o-mohlanoka

Swati: Umkhukhuma

Historical scientific names: Fagara capensis, Fagara magalismontana, Zanthoxylum thunbergianum var. capense

Zanthoxylum capense, commonly known as the Small Knobwood, is a unique evergreen tree or shrub native to Southern Africa. It's easily identified by the distinctive woody, conical knobs (each with a sharp spine!) that cover its trunk and branches. Its bright, glossy green leaves release a strong citrusy or peppery scent when crushed, and it produces small, reddish-brown fruits that reveal shiny black seeds in autumn.

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Distinguishing features:

A small, evergreen, spiny tree or shrub that can sometimes scramble.
Features distinctive conical, woody knobs on its trunk and branches, each usually armed with a sharp spine.
Has bright, glossy green, pinnately compound leaves that are strongly citrus or peppery scented when crushed.
Produces small, inconspicuous greenish-yellow to whitish flowers.
Bears small, spherical, woody fruits that ripen to reddish-brown, splitting open to reveal shiny black seeds.
Its bark and fruits have a peppery, pungent taste.

Overall appearance:

Zanthoxylum capense is typically a small, evergreen tree or shrub, though it can sometimes adopt a scrambling habit. Its most striking feature is its bark, which is covered in unique, spiny woody knobs. It has a dense canopy of attractive, glossy green leaves, contributing to a lush appearance, especially when its small fruits are present.

Height:

It typically grows to a height of 2–5 metres, but in favourable forest conditions, it can reach up to 10 metres tall.

Leaves:

The leaves are pinnately compound, meaning they are divided into several leaflets arranged along a central stalk (rachis). They are arranged alternately on the stems.
Each leaf has between 7 and 21 small leaflets, which are typically 10–40 mm long and 5–20 mm wide.
The leaflets are ovate (egg-shaped) to elliptic.
They are dark, glossy green on the upper surface and paler underneath.
The margins (edges) of the leaflets are either entire (smooth) or crenate (scalloped).
If you hold the leaves up to the light, you can often see small, translucent oil dots (pellucid glands).
When crushed, the leaves emit a strong, characteristic citrus or peppery scent.
Stipules (small leaf-like appendages at the base of the leaf stalk) are absent.
The main leaf stalk (rachis) and the petiole (leaf stalk) are often winged and can sometimes have spines.

Flowers:

The flowers are small, generally inconspicuous, and range in colour from greenish-yellow to whitish.
They are borne in panicles (branched clusters) or racemes (clusters along a single stalk) that appear in the leaf axils (where the leaf meets the stem) or at the tips of the branches.
Zanthoxylum capense is dioecious, meaning male and female flowers are found on separate individual plants.
Each flower has four petals.
Male flowers contain 4 stamens (pollen-producing parts) and a rudimentary pistil.
Female flowers have a 4-lobed ovary and 4 stigmas (the receptive part of the pistil).

Flowering season:

The Small Knobwood flowers during spring and early summer, typically from September to December in South Africa.

Fruits:

The fruits are small, spherical, woody capsules, measuring about 3–5 mm in diameter.
They are initially green but ripen to a reddish-brown or purplish-black colour.
When ripe, each capsule splits into two valves (halves) to release the seeds.
These fruits often remain on the tree for a long time, providing extended interest.

Seeds:

Each capsule usually contains 1 or 2 seeds.
The seeds are shiny black and are approximately 2–3 mm in diameter.
They persist on the opened fruit after it splits, remaining visible.

Bark:

The bark is smooth and ranges from grey to brownish-grey. Its most distinctive feature is that it is covered in characteristic conical, woody knobs or outgrowths. Each of these knobs typically bears a sharp spine. These knobs tend to be more pronounced and larger on older stems and trunks.

Stems:

The stems are covered by the distinctive bark with its woody knobs and spines. The plant's habit can range from an upright tree to a scrambling shrub.

Wood:

The wood of Zanthoxylum capense is pale yellow in colour. It is known for being hard and durable.

Thorns:

This plant is very spiny, with sharp spines located on the distinctive conical, woody knobs that cover its trunk and branches. Spines can also sometimes be present along the main leaf stalk (rachis) and petiole.

Soil type:

Zanthoxylum capense prefers well-drained soil conditions.

Aspect:

It thrives in full sun but can also tolerate partial shade. Once established, it is notably drought tolerant. It can also tolerate light to moderate frost, making it quite hardy in many South African climates.

Edibility:

While not generally consumed as a food, the bark and fruits of Zanthoxylum capense have a peppery, pungent taste and are sometimes used as a spice or flavouring agent in traditional contexts.

Toxicity:

While no general toxicity for ingestion is widely reported on SANBI, its traditional medicinal uses, such as for its numbing effect on toothache and its use as a purgative, suggest that it contains active compounds that can have strong physiological effects and should not be consumed casually.

Uses:

Traditional Medicine: This plant has a long history of use in traditional African medicine. Various parts, including the bark, leaves, roots, and fruits, are used to treat a wide range of ailments such as colds, flu, fevers, and stomach complaints. It is particularly well-known for its use as a remedy for toothache, where parts of the plant are chewed for their numbing effect. It is also used for snakebite and as a purgative.
Timber/Wood: The hard, durable, pale yellow wood is used for crafting small articles and for tool handles.
Hedges and Fencing: Due to its dense growth habit and formidable spines on its bark, Zanthoxylum capense makes an excellent and impenetrable security hedge or barrier.
Ornamental Plant: It is an attractive specimen tree for gardens, particularly valued for its unique and distinctive bark.
Spice/Flavouring: As mentioned, the bark and fruits' peppery and pungent taste can be utilised as a spice or flavouring.
Animal Food: The leaves of the Small Knobwood are an important browse source for various game animals, including black rhino and kudu.

Ecology:

Pollination: The flowers are pollinated by various insects, including bees, which are attracted to their nectar.
Seed Dispersal: The fruits are a food source for birds (such as barbets and starlings) and monkeys, which consume the fruits and help to disperse the seeds to new locations.
Browse for Wildlife: The leaves of the tree provide important forage for larger game animals like black rhino and kudu.
Shelter: Its dense and spiny nature offers excellent shelter and protection for various small animals and birds.
Larval Host Plant: Zanthoxylum capense is a crucial larval host plant for the Citrus Swallowtail butterfly (Papilio demodocus) and other butterfly species, meaning their caterpillars feed on its leaves.

Distribution and habitat:

Zanthoxylum capense is indigenous to Southern Africa and has a very wide natural distribution.

South African Provinces: It is naturally found across almost all South African provinces: Eastern Cape, Free State, Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga, North West, and Western Cape.
Beyond SA: Its natural range also extends into neighbouring countries, including Botswana, Eswatini, Lesotho, Mozambique, and Zimbabwe.
Habitat: It grows in a diverse range of habitats, such as dry woodland, bushveld, coastal dune scrub, rocky outcrops, and along forest margins. It is frequently found as a component of thorny thickets.

Derivation of name:

The genus name, Zanthoxylum, is derived from two Greek words: xanthos, meaning 'yellow', and xylon, meaning 'wood'. This refers to the yellowish colour of the heartwood found in some species within this genus.
The specific epithet, capense, is a Latin word meaning 'of the Cape'. This indicates its origin and significant presence in the Cape region of South Africa.

Historical aspects:

Zanthoxylum capense has a long and significant history of use by indigenous communities in Southern Africa. Its medicinal properties, particularly its effectiveness in treating toothache, have been recognised and utilised for generations. Beyond medicine, its hard and durable wood has traditionally been used for crafting various small articles and tool handles, highlighting its versatile importance in local cultures.

Interesting facts:

The most amazing thing about the Small Knobwood is its bumpy bark! Those woody knobs, each with a sharp spine, make it look super unique and provide great protection.
Got a toothache? Historically, people would chew on parts of this plant for its numbing effect – it's like nature's anaesthetic!
The genus name Zanthoxylum means 'yellow wood', referring to the colour of the wood in some species, though its most famous feature is definitely those knobs!
This spiny plant is a fantastic home for caterpillars of the Citrus Swallowtail butterfly – they munch on its leaves before transforming into beautiful butterflies!

Growing tips:

Propagation: You can grow new Small Knobwood plants from either fresh seeds or cuttings.
Seeds: Clean the seeds thoroughly before sowing them in a well-drained growing medium. Be aware that germination can be slow and unpredictable, sometimes taking several months.
Seed Germination Boost: To improve germination rates, you might try soaking the seeds in hot water (after cooling) or even using a method like acid scarification, which carefully breaks down the hard seed coat.
Cuttings: Semi-hardwood cuttings can be rooted successfully, especially when treated with a rooting hormone.
Growth Rate: It has a slow to moderate growth rate, so patience is key!
Soil: It prefers well-drained soil, but it's not overly fussy.
Aspect: Plant it in a spot that gets full sun to partial shade.
Watering: Once established, it's quite drought tolerant, meaning it can handle dry periods well.
Frost Tolerance: It tolerates light to moderate frost, making it suitable for many climates.
Pruning: It responds well to pruning, which can be done to help shape the plant or maintain its size.

This plant is a fantastic alternative for:

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