Warburgia ugandensis Sprague

Warburgia ugandensis is a spreading evergreen tree 4.5-30 m tall, 70 cm in diameter, bark smooth or scaly, pale green or brown, slash pink; bole short and clear of branches for about 3 m; crown rounded. Leaves alternate, simple, dotted with glands, stipules absent; petiole 1-5 mm long; blade oblong-lanceolate, elliptic or oblong-elliptic, 3-15 x 1.4-5 cm, apex and base tapering, margins entire, glossy dark green above, paler green and dull below, midrib frequently slightly off-centre. Flowers solitary or in small 3-4 flowered cymes, axillary, regular, bisexual; bracts ovate to kidney shaped, thick, 3 x 3-3.5 mm, covering only the young buds. Sepals green, ovate, 6-7 mm long, 4-4.5 mm wide; petals 10, in whorls, white or greenish-yellow, obovate 5-7 x 2.5-3 mm, dotted with glands, overlapping; stamens 10, united in a tube 4-5 mm long 2-3 mm in diameter, enveloping the ovary and most of the style; ovary oblong-elongate, 2.6-4 mm long. Fruit a berry, at first green and ellipsoidal, later subspherical and turning purplish, 3-5 cm in diameter, skin leathery, glandular. Seeds 2 or more with oily endosperm, compressed, more or less cordate, yellow-brown, 1-1.5 cm long. The genus is named after Dr. Otto Warburg (1859-1938), born in Hamburg, lecturer in botany at the University of Berlin and author of numerous botanical papers.

W. ugandensis is hermaphroditic, flowering at the beginning of the rainy season. Fruiting follows later in the rainy season; fruits may remain on the tree for a long time. In Kenya, the species flowers in December-January and seeds in May.

Soils Can withstand swamp forest soils.

W. ugandensis occurs in lowland rainforest, upland dry evergreen forest and its relicts in secondary bushland and grassland; also on termitaria in swamp forest.

Natural regeneration is primarily from seed, which germinates easily in natural forests. Artificially, W. ugandensis can be regenerated from cuttings, seedlings and direct sowing. Timing of the seed collection is important. Fruit that has fallen to the ground rots easily. The ripe fruit is collected directly from the tree or shaken off the branches and collected from the ground. Pretreatment is not necessary. Under ideal conditions, the seeds germinate within 15 days. The average germination rate of mature, healthy and freshly sown seed is 70%.

Deserves wide planting as a shapely garden or park tree, but young plants can be difficult to obtain. The bark is frequently removed for medicinal use, and care must be taken to avoid tree mortality. A fairly slow-growing tree, but once established it is hardy and coppicing can be practised.

W. ugandensis is classified as recalcitrant; however, with dry seed, viability can be maintained for 6 months at cool temperatures, storability is intermediate between orthodox and recalcitrant. In the short term, seeds can be stored in moist sawdust at 3 deg. C. Based on fruit structure, seed size and natural habitats, seed of this species may not be recalcitrant. More investigation is needed. A purity of 98% can be achieved. On average, there are 10 000 seed/kg, depending on the provenance and the climatic conditions of the ripening year.

Shade or shelter: The crown provides shade. Soil improver: Can provide green manure and mulch. Ornamental: W. ugandensis is often planted for amenity purposes.

Food: Fruit edible; all parts have a hot peppery taste. The leaves and seeds are sometimes used to add flavour to curries. Fodder: Leaves, pods and seeds are fed to livestock. Fuel: The wood has a high oil content and burns well with an incense-like smell. Timber: Heartwood yellow or greenish, becoming brown on exposure; very fragrant when freshly cut, the scent somewhat resembling that of sandalwood. Good timber for building and furniture, but not termite resistant. It saws easily, planes well and takes a high polish, but it is not durable and is liable to split on nailing. The wood somewhat resembles teak and shows a satin lustre; its fragrance persists over 4 years of storage. Milling of the wood gives rise to a dust that is very fragrant and causes sneezing. Gum or resin: The resin is used locally as glue to fix tool handles. Poison: The heartwood contains new sesquiterpenoids such as bemadienolide, cinnamide, drimenol, muzigadial, polygodial, warburganal, warburgiadione, warburgin, ugandensidial and ugandensolide. These compounds exhibit anti-feedant activity against armyworm (Spodoptera littoralis and S. exepta), widely occurring African crop pests. The anti-feedant activities of warburganal and muzigadial are comparable. These two compounds belong to the strongest group of anti-feedants against African armyworm found so far. In addition, they exhibit very potent antifungal, antiyeast and plant-growth regulating activity. Medicine: Dried bark is commonly chewed and the juice swallowed as a remedy for stomach-ache, constipation, toothache, cough, fever, muscle pains, weak joints and general body pains. It is also effective in powdered form for treating the same diseases. Fresh roots are boiled and mixed with soup for the prevention of diarrhoea. Leaf decoction baths are used as a cure for several skin diseases. The inner bark is reddish, bitter and peppery and has a variety of applications. It provides treatment for the common cold; dried and ground to a snuff it is used to clear sinuses; and it is chewed, or smoke from the burning bark inhaled, as a remedy for chest complaints. The bark, roots or leaves can be boiled in water and the decoction drunk to treat malaria, but this causes violent vomiting.