While its scented fruit is not of great value for eating out of hand, the umkokolo, often called in English kei-apple, is a useful and interesting plant. It is unexcelled for hedges in regions where the temperature does not commonly fall below 20° above zero.
The native home of the species is on the Kei River in South Africa. It is a tall vigorously-growing shrub, with rich green foliage and long, stiff, sharp thorns. The leaves are oblong-obovate, about 2 inches in length, often in small clusters at the bases of the thorns. Staminate and pistillate flowers are produced on separate plants, and both are without petals. The fruit is oblate or nearly round, bright golden yellow, and about 1 inch in diameter. The thin skin incloses a yellow, melting, juicy pulp and five to fifteen flattened pointed seeds. The flavor is aromatic, highly acid unless the fruit is fully ripe.
Because of this, the fruit is most commonly used to make jam and preserves.
Outside of its native region the umkokolo has been planted to a limited extent along the shores of the Mediterranean in France, Algeria, and Italy; in northwestern Australia; and in Florida and California. In Florida it is said to have succumbed to the cold during the severe winter of 1894-1895, and in California it has been killed by tem-peratures of 16° above zero. The usual winter temperatures in the southern parts of both states, however, are too high to injure it, and the species can be grown safely as far north as the Lake region in central Florida and favored sections of the San Joaquin Valley in California.
Botanically the umkokolo is a Dovyalis (latterly written Dory-alis), and it is sometimes listed as Aberia caffra, Harv. & Sond. Umkokolo is one of the vernacular names of its native region in South Africa. The name kei-apple is often spelled incorrectly kai-apple. The plant is not exacting in its cultural requirements, and is decidedly drought-resistant. It is most successful in a subtropical climate, and on a soil rich in humus.
Fig. 59. The umkokolo or kei-apple (Dovyalis caffra) is a large thorny shrub from South Africa, excellent for hedges. (X 1/2)
It is considered one of the best hedge plants in South Africa, since its long sharp thorns make it impenetrable. To form a hedge the bushes should be set 3 to 5 feet apart, and should be trimmed on both sides once a year. For the production of fruit, they should not be set closer than 12 to 15 feet, and both staminate and pistillate plants must be present. One of the former (male) is considered to be sufficient for twenty to thirty of the latter (female). If sufficient seedling plants are grown so that there are sure to be some of both sexes, satisfactory results will be obtained; otherwise, it is best to propagate staminate and pistillate plants by layering or some other vegetative means, and to plant no more staminates than will be required to furnish pollen.
In the Mediterranean region and in the United States, the plants flower in April and May and ripen their fruit from August to October. Seeds may be sown in pans or flats of light sandy loam. Plants propagated in this manner will begin to bear when four or five years old. Propagation by layering is practiced in Queensland, and the species will probably lend itself to shield-budding, since P. J. Wester has shown that another member of the same genus can be propagated readily in this way. The ripe fruit is sometimes attacked by the Mediterranean fruit-fly (Ceratitis capitata Wied.).