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Lost Crops of Africa: Fruits, Volume III
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Lost Crops of Africa: Fruits, Volume III 6 KEI APPLE Kei apple (Dovyalis caffra) is indigenous to the southern regions of Africa, including Malawi, Zimbabwe, Mozambique, and South Africa. Its fruits look something like small golden apples. Produced in abundance, inside their thin, tough skins is a yellow, melting, juicy pulp with a fruity aroma. Although a cultivated crop, horticulturally speaking this plant is poorly developed, and the fruits are basically underexploited. Partly this is because the plants are very thorny. Partly it is because many people don’t like the fruit’s smell. And partly it is because the pulp can be very sour. Kei apples are sour for the simple reason they have more vitamin C than oranges. Because of their tartness, they are most commonly converted into jams or other preserves soaked with sugar. However, sweeter types that are pleasant to eat raw are becoming available, and this alone seems likely to open new horizons for the crop.1 A tall and vigorous shrub with rich green foliage, kei apple2 is sometimes cultivated in orchards, but mostly grown in hedgerows and as solitary dooryard plants. It is commonly seen in hedges, forming countless rural corrals in southern and eastern Africa. In some climates the untrained plant takes on a rather scraggly appearance, but still makes an excellent hedge. Being evergreen, it provides a year-round screen, while its long sharp thorns deter both people and animals. For this reason, in the 1800s it was introduced, and is still planted, in northwestern Australia, St. Helena, littoral France, Algeria, and Italy, as well as Costa Rica, California, and elsewhere. This tough shrub does well in almost any soil, including limestone, but cannot tolerate damp sites or high watertables. It is extremely drought resistant and also tolerates salinity, even ocean spray. For this reason, it is especially valued near the sea. It is used as a windbreak and ornamental in coastal California, for example. 1 Even these selected types do not appeal to everyone. One of our contributors wrote: “I have had sweet forms of this fruit; they tasted like cold oatmeal.” 2 The word is pronounced “kye,” and refers to the river in eastern South Africa that forms one border (and the name) of Transkei. There, this fruit is known as “umkokolo.”
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Lost Crops of Africa: Fruits, Volume III The shrubby, thorny, kei apple plant produces fruits that resemble little golden apples. Indigenous to the southern zone of Africa it produces fruits in abundance. (Cori Ham) Though unexacting in its requirements for survival, the plant produces fruit best in subtropical climates and on humus-rich soils. There, it can become laden with its little golden “apples,” in some locations bearing them almost continuously year-round. In the past, the sourness of even the ripest fruits seemed a barrier to the crop’s wider acceptance. But even the sourest kinds could now have a future. In today’s markets, fruits need not be sweet to be successful. Cranberry, for example, is bitingly sour and is increasingly used in the United States just for that reason. It gives “zest” (and color) to drinks, candies, jelly desserts, and many other food products. The sweet kei apples now coming available add a new dimension. For instance, one southern California nurseryman, D. Silber, has selected a type with what he says are large, sweet fruits. He has named it “Arcadian zulufruit” and propagates it by rooting softwood cuttings. Since the plant is so productive, he claims that a single male/female pair can fill a household’s fruit needs throughout its fruiting season, which at least in southern California is most of the year. This is perhaps a glimpse of the potential inherent in this species, but the key for opening the door to the kei apple’s future is genetic selection (as is the case for most fruits). However, much more still remains to be done
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Lost Crops of Africa: Fruits, Volume III before the true extent of this species’ promise can be glimpsed, let alone fulfilled. The fierce spines are helpful in a hedge but a hindrance in an orchard. Over the years less spiny strains have been selected, but undoubtedly awaiting discovery and development, especially in Africa itself, are even less spiny ones. PROSPECTS All in all, a start has been made. However, this plant needs much more research attention before it can contribute significantly to commerce. Needed are better tasting types that are easier to produce as crops. Until then, its major role will be limited to areas where the environment will not permit better-known fruits to be grown. Within Africa As of now, the kei apple in Africa is generally restricted to subtropical areas of South Africa. Humid Areas Prospects uncertain.3 In South Africa the plant seems to thrive best where annual rainfall is 1,000-1,700 mm. However, there are good hedges of it almost everywhere in the Republic, even in the winter-rainfall Cape region. Dry Areas Prospects fair to good. The plant seems to prefer dry warm summers, but it has grown well at the Desert Botanical Garden in Arizona, where most of the year is exceedingly dry and exceedingly hot. Upland Areas Prospects good where the climate stays warm enough. Although the tree itself survives frost, the fruit crop can be lost when a late-winter freeze nips the flowers or flower buds. In the highveld of Gauteng (about 1,500 m elevation), black frosts can go further and wither the branchlets and cause the leaves to fall. Beyond Africa As above noted, the kei apple has grown well in several warm parts of the world beyond Africa. There, however, it has not yet generated much enthusiasm as a food resource. In Israel, for instance, it was once extensively cultivated as a hedge around citrus groves, but people did not like the fruits, which accumulated on the ground and became hosts for the Mediterranean fruitfly, a much-despised pest. Therefore, nearly all the plants were destroyed. Such experiences, however, do not necessarily indicate the potential of the selected kei apple strains of today or the future. 3 Some contributors said the species would do okay; others said prospects were poor.
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Lost Crops of Africa: Fruits, Volume III USES The kei apple is not an apple of course, it is a soft, apricotlike fruit with a character all its own. However, it does have similar uses. Fresh Fruit At present, most people peel the fruit, cut it in half, scoop out the seeds, sprinkle on sugar, and allow it to stand for a few hours before serving it in desserts or fruit salads. In Africa, many people (the Pedi of South Africa, for instance) add kei-apple juice to boiled grains (usually pearl millet, sorghum, or maize) to make a colorful, tasty, and nutritious porridge. This is the fruit’s greatest humanitarian potential, and is especially useful in areas where market-quality fruits can’t be grown. Many people do not like the fresh fruit at first; however, a fully ripened sample usually finds good acceptance. Unripe fruits—even “sweet” types— are so exceedingly acid they can be served as “instant pickles.” Indeed, in South Africa the young “pickles without vinegar” are served in this manner. Creative cooks also use the fresh fruits in glacés, drinks, and pastries. Processed Fruit Because of their abundance and acidity, kei apples are often prepared as preserves. They make amber-colored jellies, jams, compotes, and marmalades. The pulp is high in pectin, so only small amounts are needed to jell other fruit juices, including the most recalcitrant. A few minutes’ cooking turns kei-apple halves into a sauce that adds a fruity tang to meat, fish, or other foods. Simmered briefly in syrup the fruit produces tasty fillings for pies, cakes, or puddings. The cooked slurry can also be diluted with water and sweetened to make very refreshing drink. It is also dried into fruit leather. Slight heating helps separate the pulp from the seed. Typically, the fruits are covered with water, heated gently (far short of cooking), and pushed through a coarse sieve to remove skins and seeds. The Living Plant This plant’s use as a security hedge has been mentioned. Landowners often intertwine the shoots of young kei apple plants to form interlocking, living latticeworks that are impenetrable. These make excellent barriers against trespassers, four-legged and two-legged, and were formerly relied on around homes in South Africa’s sheep and cattle country to ward off wild predators. It is still used for this purpose in the Kenya highlands, where it is one of the most common fencing shrubs. Other Uses The plant provides good cattle fodder, made more valuable in harsh locations by the plant’s resistance to extreme heat- and drought. Because of the spines, livestock leave the foliage untouched until the desperate times arrive. This “bankable” fodder feature is invaluable. In Transkei, for example, kei-apple stock enclosures become critical for saving animals from starvation in the depths of the dry season.
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Lost Crops of Africa: Fruits, Volume III Inside the thin, tough skin of a kei apple is found a yellow, melting, juicy pulp with a lively aroma. The pulp is highly acidic for the simple reason that it contains more vitamin C than an orange. (Cori Ham) The plant makes a good support for epiphytes. In Natal, the professional and amateur growers of gorgeous orchids (such as Mystacidium capense and M. venosum) favor it as their “host.” NUTRITION The fresh ripe fruits are rich in vitamin C (80-120 mg and more per 100 g), as well as potassium (more than 600 mg).4 Sugars generally exceed 15 percent, with pectin levels nearly 4 percent. Although the protein content is low, generally below 1 percent, the balance of essential amino acids is reported good.5 Beyond that, little of this fruit’s food value is yet known. HORTICULTURE To produce fruit on a commercial scale, the trees either are laid out orchard style or are double-set in hedgerows. They can also be espaliered, training the branches onto horizontal supports. With this technique, kei apples can be grown along walls. It works well. For fruit to form both male and female plants must be present. One properly placed male is sufficient to pollinate at least 10 females. Kei apple can be propagated from seed, but this is not recommended for purposes of fruit production for several reasons: The resulting plants can 4 Wehmeyer, A. S. 1986. Edible wild plants of southern Africa: data on nutrient contents of over 300 species. Council for Scientific and Industrial Research, Pretoria. 5 Abdel Fattah, A.F., D.A. Zaki, and M. Edrees. 1975. Some investigations on the pectin and amino acid composition of Dovyalis caffra W[arb]. fruit. Qualitas Plantarum 24(3/4):311-316.
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Lost Crops of Africa: Fruits, Volume III take 5 years to flower. There is a gross excess of males. The fruit size, shape, and sweetness can differ widely between the plants. And the thorns tend to be of evil prominence. Vegetative propagation gets around all of these difficulties. The plant can be propagated from semisoft cuttings, air-layers, or budding. Such techniques assure the plant’s sex, fruit quality, and relative thorniness. Also, vegetative propagation yields fruits about 2 years earlier than seedlings because the planting materials enjoy an adult’s flowering hormones and don’t have to endure prolonged adolescence. Grafting kei apples presents no difficulties. Branches from selected plants can be grafted onto nondescript plants. Male branches can even be grafted onto female rootstock. Indeed, there is graft compatibility with an entirely different genus, Flacourtia (best known for Madagascar plum or governor’s plum, F. ramontchi). Kei apples bear consistently year to year. For optimum fruit production they need heavy pruning, no easy task with such a spiky species. For one thing, the crown needs frequent thinning because the branches tend to crowd toward the center, ending up in congested tangles of unproductive shoots. For another, the plants become cluttered at the base, making it hard to gather fallen fruits (horticulturists recommend removing all branches up to about 1 m from the ground). For a third, as many spines as possible should be pruned off to ease the harvesting and reduce the likelihood of injury to both pickers and fruits. Plants grown orchard style should be set about 3 m apart. Males need to be placed so prevailing winds blow the pollen onto the female plants. HARVESTING AND HANDLING Kei apples can be hand harvested when bright yellow and tinged with green shadowing. At this stage they are quite tart but will ripen if held at room temperature for about two weeks. As it ripens, the bright yellow skin deepens to gold and the flesh turns almost translucent. The ripe fruit’s sugar content has been estimated at averaging 15-18 percent, but even the ripest has some tartness lingering near the seeds in the center. This is not necessarily bad. Indeed, many enjoy the kei apple specifically because of this tang in the center. Fruit left on the tree will ripen to the firm, all-yellow stage, and then drop. Although classified as a soft fruit, it is remarkably bruise resistant. Small surface blemishes can be avoided by covering the ground beneath the bushes with straw or other soft material. Deeper wounds can be avoided by reducing the spines along the lower branches. An unusual quality is that once the kei apple is ripe, it resists decay. It then becomes easy to handle and has a long shelf life. However, damaged fruits soften and rot quickly, especially in a rainy, hot, and humid climate.
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Lost Crops of Africa: Fruits, Volume III LIMITATIONS The kei apple obviously has inherent promise. It has not been more fully realized because of sourness and thorniness. Many people just do not like it. In countries such as Kenya, which know the hedges well, the fruits are all but unused. In Israel (as noted) the plant grew outstandingly, but the fruits were enjoyed only by fruit flies, and this led to its rapid demise at the hands of outraged orchardists. In Florida, too, it has been far from a rousing success.6 Despite its productivity and hardiness and the promotion of less-spiny, less rampant plants, few Floridians have welcomed it, and its position has remained static for almost a half century.7 The juice stains fingers and fabrics a light yellow. Although not permanent, this can be a nuisance. This does not seem to be a good crop for agroforestry. The plant exhibits allelopathy, its roots excreting chemicals that discourage the growth of other plants in its vicinity. In addition, its roots are shallow and spreading and compete with crops for soil moisture. It is said, however, that deep-rooted crops are unaffected, so perhaps there is a place for kei apple plants in mature tree plantings. NEXT STEPS This crop deserves research and development support. It is very important to the lives of some of the world’s poorest people. The “zing” that the fruit gives to porridges and gruels cannot be overemphasized. In addition, the nutritional contribution can be important. Nonetheless, much needs to be done before the true potential of this crop can be properly judged and fully availed of. Pressing needs toward that end include the following. Superior Planting Materials Kei apple awaits a dedicated selection program, particularly to find specimens that bear fruits with less acid and better flavor. Selections can be made from already-selected germplasm of course, as well as from large seedling population derived from selected trees in the wild. Plants producing fruits more appealing to the palate can then be propagated asexually. A less thorny strain would also be important for both the fruit farmer and the nursery industry. “Many of my customers are turned away by the thorns,” reports a contributor. In addition, selections for stress and disease resistance should be sought. 6 The plant explorer David Fairchild brought large amounts of seed from the botanic garden in Durban, South Africa, to his home near Miami in 1903. For decades rare-fruit growers showed great interest in it, but this has since dwindled. An old plant is still at his home (The Kampong), but few people eat it, preferring instead the hybrid between its relatives D. abyssinica and D. hebecarpa (ketembilla). 7 Information from the late Julia Morton. Most were grafted on D. hebecarpa.
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Lost Crops of Africa: Fruits, Volume III Despite (or perhaps because of) its sourness, kei apple can give a bite as well as color to drinks, candies, jelly desserts, and many other food products. (Cori Ham) If true breeding is needed to create elite plants, it could be profitably be directed at combining high fruit quality with thornlessness, productivity, and stress and disease resistance. In this regard, it would be instructive to know more about the inheritance of thornlessness and the inheritance of low acidity/high sugar content in the fruits. A related, perhaps less urgent, line of improvement would be selection to upgrade the hedges. These might involve upright plant habit, various degrees of thorniness, sterility (so no fruits form), and ornamental value. Perfect-flowered plants are known to exist. These very rare specimens have both male and female flowers on the same plant. In commerce these self-fertile specimens may have particular value because they remove the complexity of obtaining, placing, and planting males for pollination. These dual-gender plants should be sought out, studied, and developed. Combining this species with others in its genus holds the potential for creating hybrid fruits of high market and culinary appeal. This challenging area offers more than merely interesting possibilities. Innovative amateur and professional horticulturists could find highly satisfying endeavors awaiting them here (see p. 111).
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Lost Crops of Africa: Fruits, Volume III Market Development A crop at this stage of development will not sell itself. For success, various individual efforts are needed. Likely, there are instructive experiences already in its native range. The most promising entry-level market is processed kei-apple products…pastries, preserves, things like that. One California contributor wrote, “Tina, my wife, and I are now doing this is in a small way. Results are surprisingly good. Tina’s jam is a hit; 80 percent of first-time tasters like it. I’ve also sold fresh fruit to Japan and received requests for increased supply.” Horticulture With this crop virtually all horticultural features require investigation. Among pressing needs are: Growing-System Research. Various avenues to maximize production need to be evaluated. Research should focus on such things as watering, fertilizing, pest control, pruning methods, and measures such as trellising. Harvesting Methods. Possibly something could be devised for shaking the fruit off, perhaps into a cloth screen laid below the bushes. Security Hedges. This plant’s effectiveness as a security hedge is important to document. Theft is a major problem in orchards. Will kei-apple hedges keep really dedicated thieves out of cherimoyas, mamey, or mango patches? Avocado growers in southern California are desperate for a cheap way to protect their investments. If this species works, there will be a lot of interest. Although hedges are normally grown from seed or seedlings, it is noteworthy that planting hedges of male trees would avoid problems with unwanted fruit littering the area. Food Technology With this fruit, food technologists could have a field day. Everything needs to be determined from the basic to the most sublime. Post-harvest handling studies are a particular need. Issues to document include the point at which to harvest the fruits, the ideal storage conditions, and the best packaging methods. The pectin deserves some study, also. It might well prove to have commercial potential. The use of kei apple for souring foods should be explored. In recent tests in South Africa, juice from some fruits had a pH as low as 2.5.8 The general processing of the fruits offers many special challenges.9 8 Information from Cori Ham. 9 “We have tested kei apple for cold storage and the results were very discouraging,” wrote contributor Cori Ham, of Matieland, South Africa. “Kei apple blended with guava makes a very nice fruit roll (leather), but consumer tests suggested that pure kei apple is only acceptable as a jam.”
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Lost Crops of Africa: Fruits, Volume III SPECIES INFORMATION Botanical Name Dovyalis caffra (Hook.f. & Harvey) Warb. Family Flacourtiaceae Synonyms Dovyalis caffra Warb., Aberia caffra Harv. & Sond., Aberia edulis T. Anders. Common Names Afrikaans: kei apple, keiappel, wilde-appelkoos, appelkoosdoring English: kei apple, Dingaan’s or wild apricot South Africa: umkokolo, kei apple, kei appel, Dingaan’s apple Zimbabwe: munhungura, musvisvirondo, mutsvoritsvoto (Shona); umqokolo (Ndebele) Zulu: umkokolo, iQokolo (fruit), umQokolo (tree), umbambane Other: motlhono (Sotho); muwhamba, ngundo (Vanda) Description Kei apple is a shrub or small tree that grows 3-5 m tall. The trunk and branches are a silvery gray and the leaves are borne on knobby twigs in clusters of two to five. The trees are deciduous but seem evergreen because the old leaves persist until the young ones appear. There are many sharp thorns about 5 cm long, occurring more often on untrimmed shoots than on the older branches. Cross-pollination of flowers is necessary, as staminate and pistillate flowers are produced on separate plants. Both types lack petals and are inconspicuous. As noted, occasional perfect-flowered specimens exist. Kei apples are spherical or slightly flattened (oblate) fruits. The diameter is typically 2.5-5 cm. They contain 5 to 15 pointed seeds. When ripe, they are golden yellow, velvety skinned, and crowned with a short stalk and short styles that persist from the female flower. The flesh is juicy and fragrant, with a scent that can become quite pronounced and even repugnant when the fruits get overripe. Distribution This native of southeastern Africa is abundant in the wild around the eastern Cape, Ciskei, Transkei, and Natal. It is cultivated in Gauteng (the Transvaal highveld). Mostly, however, it is planted in dooryard collections. It is rare in Zimbabwe, though sometimes cultivated there. In Mozambique, Malawi, Kenya, and Zambia it has been introduced and is cultivated to a small extent.
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Lost Crops of Africa: Fruits, Volume III As noted earlier, it has been introduced into Florida, California, Australia, and the Mediterranean basin. It reportedly has been introduced to Iran and probably other nations as well. Horticultural Varieties There are few established superior cultivars, but many good ones could be quickly developed by selecting from wild or seedling populations. Environmental Requirements Rainfall Currently, the plant mainly grows where annual precipitation is 1,000-1,700 mm. However, it withstands dry conditions. In the wild, it is found mostly in areas of summer rainfall, where the mean annual precipitation is under 700 mm. Altitude Usually this species is found in low-lying subtropical areas, from near sea level to about 1,200 m. However, in Kenya it is found up to 2,450 m. Low Temperature This shrub grows best where the mean temperatures (especially daytime temperatures) are high. However, it is fairly hardy and tolerates brief exposure to cold. In Central Florida, for example, it has withstood −5°C undamaged. High Temperature The plant’s tolerance to high temperatures is seemingly unlimited. Soil Apparently it grows well on most soil types. However, before investing in large plantings the matter should be investigated because the limits have not been clearly identified. The crop certainly needs good drainage and may perform poorly in heavy clays. Related Species In this chapter, we have concentrated on only one species, Dovyalis caffra. However, it belongs to a genus with other candidates for fruit crops. Interested amateur and commercial horticulturists could do a lot with this group, which is at present virgin horticultural territory. Various Dovyalis species offer possibilities for creating new crops or even hybrids. There is a wealth of germplasm in the genus; Africa, alone, contains at least 13 edible species of Dovyalis. All are shrubs or small trees with hairy or smooth fruits. Examples follow.
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Lost Crops of Africa: Fruits, Volume III D. abyssinica (African gooseberry, koshum) This fruit looks, tastes, and smells something like apricot. It comes from a bushy shrub that is common in forests of East Africa (Ethiopia, Somalia, Uganda, Kenya, Tanzania, Zambia, and Malawi). In Ethiopia the plant is commonly used as a hedge. The fruits provide a welcome income for young Ethiopian boys who sell bowlfuls to travelers on the main highways. The fruits are rich in vitamin C, and eaten both fresh and in jams, jellies, and desserts. The plant occurs naturally in upland rainforest and humid lower highlands (at 1,000-3,000 m in Ethiopia, and between 2,000-2,700 m in Kenya). It is frequently seen along river courses and in dry evergreen forests; sometimes in open wooded grassland. It is said to grow on most soils, provided they are well drained. For purposes of planting, ripe fruits are cracked and allowed to decay for a week before the seeds are removed. There are about 20 seeds per fruit. Ideally, they should be sown immediately in nursery beds, since they germinate readily when fresh but lose viability within a few months. It has been said that this species “produces fruit superior in quality to those of the closely related kei apple and kitembilla [South Asia’s Dovyalis hebecarpa] for eating out of hand, and when it becomes better known it will probably become more popular than either of these.” D. hispidula (bristly dovyalis) Not much has been reported about this or the other wild relatives, so the information is skimpy. This one bears spherical fruits up to 2 cm diameter. They are bright red when mature with harsh bristly hairs. The flesh is sweet tasting. D. longispinus Bright orange to red fruits. D. lucida This tree reaches 7 m in height. Its fruit is a glossy orange red. Its flavor is reportedly “sourish but not bitter or acidic.” It is said to be good for jam. D. macrocalyx (shaggy-fruited dovyalis) This species is a tree that grows on the forest margins. The fruits hide within an enlarged husk, which is hairy. They are bright red in color, and make excellent preserves. D. rhamnoides (Cape cranberry) This South African shrub produces an ovoid berry that is orange to scarlet when ripe. It is good tasting and makes fine preserves. The fruit can be used for making a thin, very tart wine, and has been used for fruit brandy. D. rotundifolia Fleshy, bright red fruits sold in the streets of Port Elizabeth and East London in South Africa.
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Lost Crops of Africa: Fruits, Volume III D. zeyheri (wild apricot, red milkwood) Fruit an ovoid berry turning orange to red when ripe. The flesh is sour and strongly flavored. The tree reaches 10 m the leaves are long and lanceolate, the flowers white and delicate. The fruits are described as astringent when raw but good for jam. Interspecific Hybrids Two hybrids between Dovyalis species are known. One appeared at USDA-Miami in 1951 when a female plant of D. abyssinica was pollinated by a nearby male D. hebecarpa. The progeny (sometimes called Florida gooseberry) are more vigorous, productive, and cold tolerant than either parent. The plants form massive mounds of vegetation (up to 4.5 m high), with all the branches weighted down with excessive crops of the brown fruits. One practical disadvantage is that when the fruit is picked its calyx remains on the plant. This leaves a cavity in the base of the fruit, making it unmarketable as a fresh fruit. However, it can be used to make syrup, jam, or other preserves. This natural hybrid has been distributed by the USDA as seedlings of P.I. 112086, Dovyalis abyssinica. The seedlings show considerable vigor, with many producing heavy yields of large-size fruits. The plants either produce perfect flowers or male and female flowers on the same plant. The fruit is yellowish brown in color and less acid than the kitembilla. Selections have been made and are being propagated by layering or grafting on seedlings of Dovyalis hebecarpa. The fruit is used like other Dovyalis species.