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<big>''[[Ptaeroxylon obliquum]]'' (Thunb.) Radlk.</big>

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{{DISPLAYTITLE:''Ptaeroxylon obliquum'' (PROTA)}}

:Protologue: Sitz.-Ber. Bayer. Akad. 20: 165 (1890).

:Family: Rutaceae

== Vernacular names ==

The wood and leaves contain chromones and other phenolic compounds. Some of these, methylalloptaeroxylin and perforatin A, showed antihypertensive effects. 7-Hydroxychromones have anti-oxidant activity. ''Ptaeroxylon obliquum'' lacks limonoids, which are commonly found in ''Rutaceae''. An alkaloid isolated from the bark showed cardiac-depressant activity. Dichloromethane extracts of roots, leaves and stems showed moderate in-vitro antiplasmodial activity.

Dioecious, usually deciduous shrub or small to medium-sized tree up to 20(–45) m tall; bole often straight and cylindrical, up to 50(–120) cm in diameter; bark surface whitish grey, longitudinally fissured in large trees. Leaves opposite, paripinnately compound with 3–8 pairs of leaflets; stipules absent; petiole flattened, rachis usually ending in a short mucro; leaflets nearly sessile, very asymmetrically oblong-lanceolate to oblong-ovate, 2–6 cm × 0.5–3 cm, cuneate at base, notched to obtuse or slightly acuminate at apex, margin entire, densely short-hairy when young but glabrescent, pinnately veined with closely spaced lateral veins. Inflorescence an axillary contracted panicle up to 5 cm long. Flowers unisexual, regular, 4-merous; pedicel up to 6 mm long; sepals nearly free, ovate, c. 1 mm long, sparsely hairy; petals free, oblong, c. 5 mm × 1.5 mm, pale yellow; male flowers with 4 stamens c. 3.5 mm long and minute rudimentary ovary; female flowers with rudimentary stamens, ovary superior, laterally compressed, 2-celled, with rather short style and 2-lobed stigma. Fruit an oblong capsule c. 2 cm × 1 cm, notched at apex, reddish brown, reticulately veined, dehiscent with 2 valves, 2-seeded. Seeds with a large terminal wing, c. 16 mm × 6 mm.

''Ptaeroxylon obliquum'' grows moderately fast: 40–100 cm/year in height under good conditions. In southern Africa trees flower in August–December when the trees are still leafless, usually just before new leaves develop. A flowering tree can be a spectacular sight. Fruits ripen about 2 months after flowering, and ripe fruits remain on the tree for some time.

''Ptaeroxylon'' comprises a single species. It has been placed in ''Meliaceae'' and ''Sapindaceae'' and in more recent floras in ''Rutaceae''. In the 1970’s it was excluded from ''Rutaceae'' into a separate family ''Ptaeroxylaceae'', together with ''Cedrelopsis'' from Madagascar and later also ''Bottegoa'' from East Africa, but a more recent phylogenetic analysis of molecular data indicated that it is better included in an enlarged ''Rutaceae''.

== Ecology ==

''Ptaeroxylon obliquum'' occurs in dry evergreen forest, often together with ''Podocarpus'' and ''Juniperus'', and in bushland, from sea-level up to 2000 m altitude. It is drought tolerant and tolerates moderate levels of frost. It accepts well-drained sandy or rocky soils, but thrives best in shale or lime soils.

== Management ==

Natural regeneration is often in forest margins, but saplings have also been recorded in ''Pinus'' plantations in South Africa. Regeneration may be abundant after severe opening of the forest canopy, and seedlings may cover the bare forest floor after disturbance. Seed can be collected just before the fruits dehisce. Pre-treatment before sowing is not necessary. The seed can be sown in an equal mixture of river sand and compost, and should be covered by a thin layer of sand. The germination rate of fresh seed is generally high, but seeds lose their viability rapidly, within a few months. One kg contains about 30,000 seeds. It is recommended to transplant seedlings when they have 3 leaves. Root suckers can also be used for propagation. Trees can be managed by coppicing, showing regrowth in about 75% of cut stems. Heart rot has been recorded as commonly present in logs.

== Genetic resources ==

== Author(s) ==

== Correct citation of this article ==

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