Sausage tree (Kigelia africana, (Lam.) Benth. 1849)

Identity

Sausage tree (Kigelia africana (Lam.) Benth., 1849) is the sole species of Kigelia, a genus in the Bignoniaceae family. ^{1 7}

A Mozambican vernacular term for the sausage-shaped fruit gave rise to Kigelia. The epithet africana reflects a distribution across much of the continent. Lamarck first described the species as Bignonia africana in 1785; George Bentham transferred it to Kigelia in 1849, creating the combination accepted today. ¹

The name sausage tree describes the long, cylindrical hanging fruits. They give the tree its most recognizable outline for much of the year. ²

Recognition

A dense, rounded crown and semi-evergreen foliage characterize Kigelia africana. It commonly reaches 10–20 m (33–66 ft), with exceptional trees reported at 23–25 m (75–82 ft). Its short, stout trunk has light-brown bark that flakes away in thin plates. ^{2 3}

Compound leaves cluster near branch tips, each with three to five pairs of leathery, glossy leaflets. Long, drooping panicles can approach 1 m (3.3 ft) and carry trumpet-shaped flowers 5–12 cm (2–5 in) across. Maroon to purple with yellow veins, the flowers have a musky scent that attracts epauletted fruit bats, the principal night pollinators. Charaxes butterflies and several nectar-feeding birds also visit after the flowers open. ^{2 3}

Huge woody berries, gray to brown, hang from long stalks. A fruit can reach 1 m (3.3 ft) long and 18 cm (7 in) across, weighing as much as 12 kg (26 lb). There is no second species in the genus with which to compare this fruit: Kigelia is monotypic. ^{3 4}

Useful taxonomy

The accepted combination, Kigelia africana (Lam.) Benth., derives from Lamarck’s original Bignonia africana Lam. 1785. Two subspecies are recognized: the widespread Kigelia africana subsp. africana and the East African Kigelia africana subsp. moosa (Sprague) Bidgood & Verdc.. ¹

Older synonyms include Kigelia pinnata (Jacq.) DC., long used in horticultural and pharmacological writing, and Kigelia aethiopum (Fenzl) Dandy. About ten other regional names were described separately before being brought together under one taxon. Kigelia pinnata still appears frequently in recent medical publications, explaining its persistence outside current taxonomic databases. ^{1 7}

Habitat and range

Across tropical and southern Africa, the native range stretches from Senegal and Sudan to KwaZulu-Natal in South Africa, with populations recorded in more than thirty countries. Sausage tree grows in moist savanna, gallery forest and along waterways, from sea level to about 3,000 m (9,840 ft), in areas receiving 900–2,000 mm (35–79 in) of annual rainfall. ^{4 2}

The International Union for Conservation of Nature lists sausage tree as Least Concern. Its broad continental range buffers it against an overall decline, although agricultural deforestation and overharvesting for cosmetics and traditional medicine exert local pressure in West Africa. ⁶

Outside Africa, cultivation as an ornamental curiosity occurs in tropical and subtropical climates, including India, Mauritius and Australia. In frost-prone temperate places such as mainland France, it needs a heated greenhouse or botanical collection because it lacks frost resistance. ³

Life cycle and reproduction

Night-opening flowers develop successively along hanging panicles, which carry several dozen blooms. Each flower opens for only one night before fading, restricting its pollination window to nocturnal visitors. Epauletted fruit bats perform most pollination; dark color, musky scent and night opening are characteristic adaptations to bat visitors. ²

Seeds need no obligatory pretreatment and germinate in 10–25 days in warm, moist substrate, although success rates are often low. There are roughly 9,700 seeds per kilogram (2.2 lb). Young trees grow quickly in favorable climates, about 1 m (3.3 ft) a year, producing a shade-giving outline within 4–5 years. Flowering starts at about 6 years. Fruits take several months to ripen before falling or rotting on the ground, contributing to natural regeneration. ⁴

Uses and risks

Raw or immature fruit is toxic and purgative to humans. It can cause mouth blisters and skin blisters after prolonged contact, and is never eaten unprocessed. Dried, roasted or fermented fruit traditionally flavors some beers, while roasted seeds serve as famine food during shortages. ^{2 4}

Traditional African medicine uses the bark, leaves and fruit for ulcers, wounds, skin conditions and some digestive or respiratory complaints; extracts also enter commercial skin cosmetics. Unlike the unprocessed fruit, foliage and bark have no documented toxicity in contact with domestic animals. ^{4 3}

Medium-density wood provides boards, dugout canoes and tool handles. Roots yield a yellow dye, while hollowed fruits traditionally become rodent traps or carved objects. Vigorous, spreading roots mean trees must be planted well away from foundations. ^{4 2}

Varieties, look-alikes and related plants

Established horticultural cultivars comparable to those of familiar houseplants are absent from Kigelia africana. The recognized division is botanical, between the typical subspecies and East African subsp. moosa. Specimens sold as collection curiosities are otherwise young seedlings kept in pots, with no particular varietal status. ¹

Since Kigelia contains a single species, confusion mainly concerns the scientific name in use. Many publications, especially pharmacological ones, retain Kigelia pinnata, which can suggest two separate taxa even though it denotes the same tree. From a distance, the silhouette and hanging fruits can also suggest other large African trees, such as Adansonia digitata; its fruit, however, is an oval capsule rather than a long cylinder.

Main sources

• Plants of the World Online / Kew, Kigelia africana (Lam.) Benth.
• PlantZAfrica / SANBI, Kigelia africana
• Useful Tropical Plants, Kigelia africana
• World Agroforestry Database, Kigelia africana species profile
• CABI Compendium, Kigelia africana (sausage tree)
• IUCN Red List, Kigelia africana assessment
• GBIF, Kigelia africana (Lam.) Benth. species record