Irvingia wombolu Vermoesen

Irvingia wombolu is a tree to 25-30 m tall, butressed up to 2 m. The stem is often leaning and glabrous. The first branches are usually at a height of 7-10 m. Foliage regular, not as dense as in the Irvingia gabonensis. Leaves simple, alternate, entire, obovate, and less leathery, length 10.5-14 cm, width 4-8.5 cm, leaf apex rounded, often with a barely distinct blunt acumen, base obtuse to acute, occasionally very shortly cuneate. Leaf stipules leave an annular scar around the stem when they fall off. Fruit with green skin which may turn yellow on ripening. Flesh of fruit yellow, soft, juicy and fibrous, extremely bitter and inedible. When the flesh rots away the fruit the shell may have some curly fibres attached to it. The shell wall is less than 7 mm thick and is easy to break open using a wooden club or a stone. This tree closely resembles Irvingia gabonensis, genetic data indicates significant differences between the two, supporting (Harris 1996) conclusion that the taxa are distinct genetic entities. The genus name commemorates E.G. Irving, 1816-1855, a Scottish botanist.

I. wombolu flowers at the end of the rainy season (October-November), but depending on conditions, flowering time overlaps in some years and regions. Fruiting is at the end of the dry season (February-April). The flowers, appearing 6-10 years after planting, are insect pollinated. There is no evidence of hybridization with the closely related I. gabonensis. There is a decrease in genetic similarity over distance. Results from RAPD analysis indicate marked (similarity estimates) differences between Cameroonian and Nigerian material. Southern Nigeria and southern Cameroon material harbour rare alleles and significantly high levels of genetic diversity. Fruits passed out in elephant dung show successful germination. Red forest pigs and squirrels open the pyrenes eating the seeds only.

Prefers dry or seasonally flooded soils.

The bitter bush mango shows a wider rainfall regime tolerance than the other Irvingia species. It occurs in dry land forest in areas with more than 1 500 mm rainfall across the southern half of the Central African Republic from Cameroon in the west to Sudan in the east. In some localities it is common in swamps and seasonally flooded forest than in adjacent dry land forest.

I. wombolu is well known and has been utilized for a long time in Nigeria and parts of Cameroon. Reports of cultivation of this species are given. So far no reliable reports of wild I. wombolu in forests are recorded. The bitter bush mango fetches high prices in cross-border trade contributing significantly to the economy of the central and west African region as a whole.

The members of the genus Irvingia are fire tender.

Germination is epigeous and phanercotylar, beginning at about 1 month and occuring faster under the mother tree. The seeds of I. wombolu are recalcitrant and should be sown fresh.

Shade or shelter: The bitter bush mango provides adequate shade. Intercropping: I. wombolu has high agroforestry potential. In its native range it is found cultivated with other crops in farm systems.

Food: The seeds are collected and their cotyledons grilled or dried in the sun, pounded then used in preparation of a local dish 'gumbo'. The mesocarp is inedible. I. wombolu seeds give a more mucilaginous texture to food, this attribute makes the seeds command a higher market price. Overcooking causes the loss of sliminess. The sauce keeps for several days without refrigeration. The dried kernel can be stored for up to a year, as can the paste if it is thoroughly dried in the sun. Apiculture: Insects visit the flowers for pollen. Medicine: The fresh bark of the tree is considered to be a powerful antibiotic against scabies, a cure for diarrhoea when mixed with palm oil and a toothache remedy.