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Sneezewood
Ptaeroxylon obliquum
SA tree no: 292
English: Sneezewood, Cape Sneezewood
Afrikaans: Nieshout, Kaapse Nieshout
Xhosa: umThathi
Zulu: umThate
Namibia: Omumbungururu
Historical scientific names: Ptaeroxylon utile, Ptaeroxylon obliquum var. latifolia
Ptaeroxylon obliquum, commonly known as Sneezewood, is a medium-sized, semi-deciduous to deciduous tree famous for its incredibly hard, durable, and aromatic timber. The tree gets its common name from the dust released when its wood is sawn or oils released when its leaves are crushed, which can cause sneezing.
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Distinguishing features:
Finely textured, bright green, pinnately compound leaflets that are distinctly asymmetrical in shape.
It is the only indigenous South African tree with opposite, paripinnate leaves (a type of compound leaf in which the leaflets are arranged in pairs along a central axis -the rachis - and the leaf ends with a pair of leaflets at the tip, instead of a single terminal leaflet).
Aromatic leaves that have been said to cause sneezing when crushed.
Small, inconspicuous, greenish-yellow flowers.
Small, two-lobed, winged fruit.
Beautiful, often fluted or twisted trunk with pale, flaky bark.
Highly durable and termite-resistant wood.
Overall appearance:
Ptaeroxylon obliquum typically grows as a medium-sized tree with an upright, somewhat spreading crown. Its bark is often pale and flaky, and its leaves have a characteristic fine texture. It is, however, extremely variable depending on its habitat and can range from shrub-sized to a fairly large tree. Leaf colour can also vary.
Height:
Sneezewood can reach impressive heights of 20 to 35 metres, although in montane forests it more commonly grows to around 10 metres, while in bushveld and drier regions it remains a smaller tree or shrub, seldom exceeding 3 metres.
Width:
It can spread to a width of 5 to 10 metres.
Leaves:
The leaves are alternately arranged and pinnately compound, meaning they have multiple leaflets arranged along a central stalk (the rachis).
Leaves are paripinnate (the leaf ends with a pair of leaflets at the tip, instead of a single terminal leaflet).
Each leaf consists of 3-7 pairs of relatively small, oblong to elliptical leaflets, each 3-8 cm long and 1-3 cm wide.
A distinctive feature is that each leaflet is distinctly asymmetrical or 'skew' (oblique), giving the species its name.
The leaves are glossy, bright green, and hairless.
When crushed, they release a strong, pungent, peppery aroma that can cause sneezing.
The tree is semi-deciduous to deciduous, losing its leaves in autumn or during dry periods, turning a lovely golden colour before falling.
Flowers:
The flowers are very small (about 3 - 5 mm in diameter), sweetly scented, with four petals, opening light yellow with an orange centre from creamy yellow buds.
They are borne in slender, branched clusters (panicles) in the leaf axils.
Ptaeroxylon obliquum is functionally dioecious, meaning individual trees bear either male or female flowers, or predominantly one sex, so both male and female trees are generally required for fruit production.
Flowering season:
It generally flowers in spring, from August to September, often before or as the new leaves emerge.
Fruits:
The fruit is an oblong capsule (1.5-3 cm), notched at the tip.
They are initially green, ripening to a pale brown or yellowish-brown colour.
When ripe, they split open to release the winged seeds.
Seeds:
The winged seeds are about 5 mm long and dispersed by the wind.
Bark:
The bark is a distinctive feature. On younger trees, it is smooth and greyish, but as the tree matures, it becomes pale grey, often fluted or twisted, and characteristically flakes off in large, irregular patches, revealing yellowish or reddish-brown underbark. This flaky appearance gives it a rather mottled look.
Wood:
The wood is extremely hard, dense, and durable, highly prized for its resistance to rot, insects (especially termites), and marine borers.
It has a distinctive yellowish-brown colour with a greenish tinge and a fine, even grain.
It is highly aromatic, contributing to the sneezing effect when cut.
It is often used for fence posts, railway sleepers, furniture, flooring, and boat building.
Roots:
It has a well-developed, strong root system that helps it anchor in diverse terrains.
Soil type:
It is adaptable to a wide range of soil types, including sandy, loamy, and rocky soils, provided they are well-draining. It can tolerate nutrient-poor soils and prefers slightly acidic to neutral conditions.
Aspect:
Prefers full sun but can tolerate partial shade, especially when young. It is relatively drought-tolerant once established but benefits from moderate moisture. It is sensitive to severe frost, especially when young.
Edibility:
Not considered edible. The leaves are irritant.
Toxicity:
The sawdust and crushed leaves are highly irritant and can cause sneezing, respiratory problems, and irritation of the mucous membranes in sensitive individuals.
Prolonged exposure to the sawdust can lead to chronic respiratory issues.
It is toxic if ingested.
Uses:
Sneezewood produces exceptionally durable, pest- and decay-resistant timber valued for heavy-duty uses such as fence posts, railway sleepers, poles, mining timber, furniture, flooring, and boat building.
Traditionally it was used for hut poles, knobkieries, walking sticks, ornaments, and especially xylophone keys, prized for its golden-brown colour and natural lustre.
The wood, sawdust, bark, and resin have all been used in traditional medicine and as insecticides, though their irritant properties require caution.
Highly flammable, the wood burns “like paraffin,” making it excellent fuel historically used for iron-smith furnaces and even as tinder for fire by friction.
Ecology:
The Common Citrus Swallowtail butterfly (Papilio demodocus) is frequently seen visiting and breeding on this tree, as it does on other members of the Rutaceae (citrus) family.
The young foliage is browsed and enjoyed by game including various antelope and giraffe.
Distribution and habitat:
Ptaeroxylon obliquum is indigenous to South Africa and is widely distributed across the Eastern Cape, KwaZulu-Natal, Mpumalanga, Limpopo, and parts of the Free State.
It occurrs in woodland, scrub forest, and evergreen montane forest.
It is particularly common in the Albany Thicket and Eastern Cape forests.
Beyond South Africa, its range extends northwards through southern Africa to Tanzania.
Derivation of name:
Pronounced 'teroxillon', the genus name Ptaeroxylon comes from Greek: "ptaero" (to sneeze) and "xylon" (wood), directly referring to the sneezing reaction caused by its sawdust.
The species name obliquum is Latin for "oblique" or "skew," referring to the distinctive asymmetrical leaflets.
Common names like "Sneezewood" and "Nieshout" (Afrikaans for sneeze-wood) directly reflect this distinctive property.
Until recently Sneezewood and the Madagascan Cedrelopsis were in their own family, Ptaeroxylaceae, but recent DNA evidence put it squarely in the Rutaceae (the citrus family).
Historical aspects:
Sneezewood has a long and storied history in South Africa, valued by both indigenous communities and early European settlers for its exceptional durability.
Its timber was extensively used for fence posts (sometimes entire “sneezewood fences” enclosed properties), building structures, and especially in the mining industry for props and sleepers.
Large quantities were also felled for fuel, contributing to its scarcity today. Palmer & Pitman (1973) in Trees of Southern Africa note that sneezewood once fueled five lime kilns at Bathurst and powered the steam tugs at the Kowie (Port Alfred).
Heavy demand for its wood led to widespread over-exploitation, and it is now a protected species in South Africa—legally safeguarded from cutting or disturbance without a permit, underscoring its ecological and cultural importance.
Until recently, Sneezewood and the Madagascan Cedrelopsis were classified in their own family, Ptaeroxylaceae, but modern DNA evidence firmly places them within the Rutaceae—the citrus family.
Interesting facts:
This tree is basically nature's own pepper spray! If you sniff its sawdust or crush a leaf, you'll probably let out a massive sneeze. That's how it got its name!
Imagine building a fence that lasts for over a century – that's the superpower of Sneezewood! Its timber is so strong and bug-proof that fence posts made from it can stand for more than 100 years.
Even though it causes sneezing, the wood has a lovely, spicy, peppery scent when it's freshly cut. It's an aromatic powerhouse!
Look closely at its leaves, and you'll see a little secret: each leaflet is distinctly lopsided or 'skew' at its base. It's a subtle way to identify it.
The city of Umtata in the Eastern Cape is named indirectly after the Xhosa name for the tree, "umThathi."
Growing tips:
Seed is easy to germinate if undamaged by insects.
Collect seed just before capsules split and sow in a 1:1 mix of river sand and compost, and cover lightly with sand.
Transplant seedlings at the 3-leaf stage.
Young trees planted in open soil need good watering to establish.
Growth rate is moderate to fast (0.4–1 m per year).
Tolerates moderate frost and is highly drought-resistant, though it grows best in higher-rainfall areas.
Prefers shale or lime-rich soils but will thrive in most well-drained sandy or rocky soils.
Which is which?
The Sneezewood is often confused with the Clausena anisata (commonly known as Perdepis or Horsewood) when not in flower or fruit as the leaves are very similar. The easiest way to tell them apart is by the terminal leaflet... Sneezwood doesn't have one making it paripinnate. Clausena anisata is imparipinnate, meaning the compound leaf ends with a single terminal leaf.
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