Lost Crops of Africa: Volume III: Fruits (2008)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

8 IMBE Asia’s mangosteen is commonly called the world’s most delicious fruit. However, the plant producing it (Garcinia mangostana) happens to be only one of 400 Garcinia species found in Asia and Africa. Some of the lesser- known examples also have delicious soft fruits, while others produce chewy nuts described as “falling somewhere between fruits and chewing gum.” Africa’s best-known mangosteen relative is the imbe,1 a tree whose soft and colorful fruits brighten up markets from Senegal to South Africa. Its botanical name, Garcinia livingstonei T. Anderson, derives from Dr. David Livingstone. In the East African area through which the legendary explorer wandered during the 1860s, imbe is known as “the King of Fruits.” The pulp of these small, orange-colored delights is juicy, pleasant, and sweet-to-acid on the tastebuds. Even those specimens that are unusually sour are considered agreeable and refreshing on a hot afternoon. Imbes come from a shrub or small tree with a dense spreading or conical crown topping a short, often twisted trunk or cluster of trunks. The effect is a tree that seems to grow strangely off-kilter. Its unsymmetrical shape and stiff, dark leaves create a striking appearance. This unusual and eye-catching form, together with the year-around foliage and heavily scented flowers, make it a landscaper’s dream. As a result, this tree is today planted more for beauty than for food. It has, for example, long decorated Mozambique’s capital. Many Maputo streets are lined with imbe trees, providing shade to all and fruits to some (mostly kids waiting for the bus to school). Imbes also beautify the landscape around the famous Victoria Falls.2 But in the opinion of many who know this species, the imbe is a candidate for domestication and for much more intensive use in Africa’s lowland tropics and hotter subtropics. A host of specific reasons support this opinion: Many African peoples already relish the fruits. Even in its present 1 Commonly also called wild plum, wild mangosteen, pama, gupenja, and mwausungulu. 2 “I’ve just come back from the Zambezi Valley below Victoria Falls Gorge,” wrote Ray Perry, one of our contributors. “The Garcinia were in full blossom (September). What a wonderful smell. The trees were alive with insects and birds. Bees obviously love the flowers. There was also a small moth around the trees. There are many 10 m tall specimens, but the species seems to only grow along the river courses.” 291 

292 LOST CROPS OF AFRICA This eye-catching imbe tree with a dense crown makes a striking sight. This, together with the year-around foliage and heavily scented flowers, make it a landscaper’s dream. As a result, this tree is today planted mostly for its good looks. However, the plant happens to be related to Asia’s mangosteen, generally considered the “world’s most delicious fruit.” Imbe’s colorful fruits brighten up markets from Senegal to South Africa but they have yet to be produced in anything like substantial commerce. (Steve Flowers) unimproved state, the species produces abundantly. The trees integrate well into the village scene and make excellent partners in mixed-crop farming. Farmers are almost promised a profit because the general populace places a high value on these fruits—indeed, demand is so great it often cannot be filled. The fruits themselves are already attractive and of a good size for mass marketing. The trees are adaptable and thrive in adverse sites, including dry, damp, sandy, or rocky locations. Although not overly particular as to soil, the trees respond vigorously to good culture. Finally, they make excellent village-, farm- or dooryard companions, being tall enough to throw soothing shade over people, paths, and patios. Unfortunately, however, little is currently known about how to grow this plant as a food crop. Despite common occurrence and widespread popularity, its production under cultivated conditions remains basically undocumented. Given this paucity of experience, imbe’s commercial future must therefore be considered uncertain. Nonetheless, further horticultural exploration should be undertaken with vigor, as this seems likely to unleash a new, nutritional, and notable indigenous resource. Even without their fruits, these highly ornamental trees are good to have around. Seen in profile, they frequently divide near the ground into three or four upright, outward-curving trunks that carry short, stiff, lateral branches. 

IMBE 293 They can reach 10 m in height, but are normally much less. The new shoots grow in whorls (verticils) of three and emerge at an acute angle from the stem, giving the tree its characteristic asymmetry and crooked form. Imbe trees are normally described as being dioecious (male and female flowers occurring on separate trees). Both sexes flower prolifically, and the quantities of pollen and nectar they produce attract large numbers of insects, which in turn attract large numbers of birds, making imbe trees a boon to the environment. As the season progresses the trees become loaded with ripe fruit and take on an even more exceptional appearance. Each fruit looks like a small plum: yellow-orange-red in color and round or ovoid in shape but it has a point at the bottom. The skin—thin, smooth, glossy, and leathery tough—separates easily from the flesh. The pulp itself is yellow and watery, with a pleasing flavor—sweet, and not unlike a perfect peach. In the center are one or two seeds which, unlike its relatives, are not reported as eaten. On the downside, these seeds are about the size of small dates and are quite large in proportion to the overall fruit, making the pulp correspondingly thin. Also, the pulp clings to those stones in the center. In addition, unripe pulp can contain latex, which tends to stick to the consumer. The fresh fruits are eaten raw or are commonly cooked with porridge and other cereal products. Once the seeds are removed, the flesh can be sun- dried and stored like a pitted prune. The fruit is also crushed like grapes to create a drink. Indeed, fermented beverages are sometimes prepared. One of these is a purplish, claret-like wine; another is a liqueur made by soaking the fruits in alcohol and thickening the extract with syrup. NEXT STEPS Africans, like people everywhere, value certain trees more than others, and superior trees are already well known in various locations. These offer opportunities for rapid horticultural advancement. Among the first things to be done, therefore, is to locate, identify, and compare these special types. This process of genetic selection offers to considerably improve characters such as sweetness, appearance, rind toughness, pulp thickness, latex content, fruit size, seed size, and maybe freestone quality. It should be possible to increase the thickness of the pulp by seedling selection; likely they already exist. The culinary preferences of the local inhabitants also may have been subjected to selection, so superior types that reflect flavor and other local preferences may well be available. Precocity, prolificacy, tree size, and regularity of bearing are additional important horticultural attributes that likely have been selected for. The key to turning imbe into a viable fruit crop lies in the vegetative cloning of select specimens. Both male and female specimens can be vegetatively propagated by air layering or grafting. Budding is probably feasible as well. 

294 LOST CROPS OF AFRICA The small, orange-colored imbe provides a pulp that is juicy, pleasant, and sweet-to-acid on the tastebuds. East Africans have dubbed it “King of Fruits.” Even those specimens that are unusually sour prove notably appealing on a hot and sweaty afternoon. (© TopTropicals.com) There is also, however, the possibility that imbe is one of those rare plants that can clone itself through its own seeds (a process known in botany as apomixis). In various places several generations of trees grown from seed have yielded plants exactly like their parents…with no apparent variation among all the progeny. Also, it is said that female flowers that have been bagged (to keep all pollen out) can produce normal fruits and set viable seed.3 This pollenless fruit production obviously has important implications for selection—some trees will produce apomictic seeds, which grow true-to- type, while other trees produce sexual seed, which express various gene blends. The apomixis would greatly aid selection and virtually guarantee clonal purity. In addition, male plants would not be needed in any planting 3 Imbe’s famed Asian cousin, the edible, cultivated mangosteen (Garcinia mangostana L.), is an obligate agamosperm (creating unfertilized, clonal embryos), which arose in cultivation and does not occur in the wild. Reproduction is entirely asexual. Fruits grow parthenocarpically on female trees, and seeds maintain trueness-to-type. Richards states that imbe is a probable facultative agamosperm. In other words, it is likely imbe reproduces both by apomixis (like mangosteen) and/or by normal sexual reproduction between male and female trees. Richards, A.J. 1990. Studies in Garcinia, Dioecious Tropical Forest Trees: Agamospermy. Bot. J. Linn. Soc. 103(3):233-250 (this is the first of three seminal articles detailing the long-mystifying origin of the Asian mangosteen). 

IMBE 295 (indeed, as in certain other species, males might be mere nuisances). Best of all, good types could be replicated via the simplest and cheapest method: planting seeds. Obviously, further research to clarify these aspects—which could rapidly open this crop to major new production with little fuss or fumbling—is urgently needed. Virtually no research on the horticultural requirements has been done to date. In a sense, everything about cultivating imbe needs investigation. In particular, conventional vegetative propagation needs to be researched. Even if apomixis proves to be real, reliable, and practical, grafting onto selected rootstocks might still be beneficial. Other unknowns that need answering include: Is pollination sometimes necessary or beneficial? What are the optimal sex ratios in cultivated pollinating populations? How densely should the trees be planted? Should they be pruned? If so, when? And how? It is known that the seeds germinate readily if they are fresh and are kept moist and warm. Also, the seedlings are said to transplant easily. The problem is that they subsequently grow too slowly for most people.4 This slowness will likely be overcome by vegetative propagation, which is known to slash the time-to-first-flowering in many crops.5 Little is known about handling imbe fruits. The rather tender skin would seem to limit the possibility of shipping imbes long distances, but so many other fragile fruits are routinely transported across the oceans these days so it may be less of a limitation. In addition, the imbe deserves to be more widely cultivated as a backyard fruit, where the question of shipment is moot. This topic is clearly connected with the strength of the skin. Not all the fruits are thin skinned. Some have a thick hide, a genetic quality that could be most valuable and vastly change imbe’s prospects. Special areas for fascinating research into the greater use of this resource include the following. Environmental Improvement The plant is surprisingly drought resistant and may find use in efforts to combat early stages of desertification. Yet another interesting environmental benefit deals with imbe’s potential as a hedge. Although normally a tree, it can be planted close together and clipped to form a low and solid hedge. Given the dense and evergreen foliage, imbe hedges might find many uses. They might, for instance, be planted around fields and gardens. Imbe hedges planted on the contour across the hillslopes 4 “We’ve successfully grown Garcinia livingstonei and have many in the nursery but they don’t sell because they’re so slow growing. We keep on planting them though out of responsibility to future society. One day they’ll be large and everyone will be wanting them. Fresh seeds germinate very easily in moist mulch but are not viable once they’ve dried out.” Ray Perry. 5 Even without vegetative propagation it could have a future. Imbe certainly grows faster than the true mangosteen, which begins rapid growth only after 5 to 7 years and fruits heavily only after 6 to 12 years and has nonetheless become a major crop in Asia. 

296 LOST CROPS OF AFRICA may provide excellent edible erosion control. Similar close-spaced plantings could mark compound boundaries, pathways, property lines, and so forth. In such cases fruits could be a secondary product or at least a contribution to the diets of wandering children or animals. Food Technology There is much potential for processing into fruit-based products such as juices and pulps. This needs exploration. The rind is rich in pectin, potentially making imbe an excellent ingredient for preserves, jams, and jellies. Health Research Perhaps there are medicinal benefits to be gained from the imbe. Extracts of leaves and flowers apparently have antibiotic properties. The sap is said to be bactericidal. Subbing for the King Imbe might also prove especially useful in extending mangosteen production to Africa. The two are so closely related that imbe is likely to provide a rootstock onto which its cousin can be grafted. This combination may have considerable commercial significance for extending the mangosteen’s range beyond Asia and perhaps beyond the humid tropics. This would put mangosteen on the lips of millions who can now only dream of what the “world’s most delicious fruit” must taste like. Environmental Requirements As to where imbe cultivation should be attempted, no one can be certain. Natural stands may or may not be a guide in this regard. However, based on those natural stands one might consider: Temperature Despite an ability to survive light frost, this plant must be regarded as heat loving and likely to perform best in tropical lowlands and the hot subtropics. In cooler subtropical climates where, for example, the navel orange achieves best quality, the imbe grows too slowly to be commercially viable. In the lowveld as far south as KwaZulu-Natal, it typically occurs where mean annual temperature is 20-22.5°C and frost never occurs. This is the most southerly distribution of what is essentially a tropical tree.6 In Botswana, imbe is fairly common around the huge inland delta known as the Okavango. Here, and to a lesser extent in Namibia’s Caprivi Strip, light ground frosts occur during the coldest winter months, but winter days are warm and the summers extremely hot. Mature imbes are reported to withstand 7°C below freezing without serious injury. 6 The immediate, low-lying coastal strip to approximately Durban is probably the southerly limit in terms of heat unit accumulation for satisfactory growth. 

IMBE 297 Soil Trees are found on sandy or dry rocky sites as well as in coastal areas. Soils vary from deep sands to heavy alluvial soils along riverbanks. Moisture Although many grow beside rivers, on floodplains, or other locations with high watertables, others grow in fairly arid locales. It tolerates dry seasons as long as 5 months with ease and withstands fire as well. Like many arid and fire-resistant trees, these robust plants have a bulbous base underground. At the same time, the species grows satisfactorily in most soils BITTER KOLA Probably all the 400 Garcinia species have edible fruits. Among other African species worth research attention is Garcinia kola. Known in commerce as bitter kola,7 this is a species of tropical West Africa, perhaps most famous in Sierra Leone. The pulp of the fruit is good, having a sweet/sour taste, but it is hardly known even where the tree is widely grown. Seeds are currently the important product, and are seen in markets from Senegal to southern Nigeria, Cameroon, and deep into the interior. They are chewed like cola nuts (the source of ingredients in drinks such as Coca- Cola® and Pepsi-Cola®). They are bitter, astringent, aromatic, and taste somewhat like coffee beans, followed by a slight sweetness. A contributor in Ghana, Albert Adai Enti, urged this species’ inclusion: “The seed of Garcinia kola is little known,” he explained, “only because the amount sold in the markets is insignificant and many people do not notice it. In addition, the wood is a popular chewstick, which is used mostly to clean the teeth. It is sold everywhere and used by almost everybody. So people hardly allow the tree to grow to fruiting age before they cut it. The result is that only a few trees, fortunately hiding in remote areas, are able to fruit but cannot produce enough to meet commercial demand. “So although the seed is a good chewable food, it has never been popular. At present, Cola nitida, the true kola, is the most popular chewed seed, which is also meeting commercial demand for export. But if Garcinia kola can be established in plantations and protected, the fruits will certainly be produced and used in the same way as Cola nitida. It is a rainforest tree species and the seed germinates well. It may be slow growing but will grow by all means if left undisturbed. I am sure it could be an economic fruit tree once established and controlled.” Adding to this species’ potential is the fact that Africans use the small branches every day as disposable toothbrushes. The twigs have recently been shown to contain antiseptics, and thus seem likely able to maintain healthy teeth and gums. The seeds are also added to palm wine to make it “stronger” in its effects. 7 It is also called false kola, kola male, or kola bitter. 

298 LOST CROPS OF AFRICA This plant is a highly valued ingredient in African traditional medicine. Throughout West Africa it has been employed in folk medicine as rejuvenating agent and general antidote. Confirmatory discoveries have recently been made by researchers working in prestigious medical research facilities in the United States and elsewhere. In this work, bitter kola seeds have been shown to contain a complex mixture of biflavonoids, benzophenones, and xanthones. The biflavonoids have demonstrated many pharmacological effects, among them antiviral, anti-inflammatory, antidiabetic, bronchodilator, and antihepatotoxic properties. The benzophenones showed antimicrobial activity in other studies. Some proprietary dietary supplements containing Garcinia kola extractives already exist in African and Western markets. Among the myriad African Garcinia species, a sampling of the “best known” includes: Garcinia afzelii West tropical Africa, fruits chewed like cola. Garcinia buchananii Tropical Africa. Garcinia buchneri Southern tropical Africa. Garcinia cernua Voahandrintsahona. Madagascar. Garcinia conrauana Southern tropical Africa. Garcinia gerrardii Umbini. Large shrub of Natal and adjacent territory. The fruits are orange, ovoid, and big (up to 2.5 cm long). Garcinia huillensis Yellow plum-like fruits; juicy yellow flesh. Garcinia kingaensis Excellent fruits, but very acid. Garcinia ovalifolia Tropical Africa. Garcinia polyantha Tropical Africa. Garcinia wentzeliana Mogola. This woody climber of tropical Africa, bears sweet, juicy, agreeable fruits that look like grapes.