For its ornamental value as well as its edible fruits the carissa deserves to be cultivated throughout the tropics. Within the last few years it has become fairly common in southern Florida, and it has been found to succeed in southern California.
The plant is a large, much-branched and spreading shrub, reaching 15 or 18 feet in height. It is armed with stout branched thorns, and the dense foliage is deep glossy green in color. The leaves are ovate-acute, mucronate, thick and leathery, and 1 to 2 inches long. The flowers, which are borne in small terminal cymes, are star-shaped, fragrant, and about 2 inches broad. The plant blooms most profusely in early spring, but produces a few flowers throughout the year. The fruits, most of which ripen in summer, are ovoid or elliptic in form, 1 to 2 inches long, with a thin skin inclosing the firm granular reddish pulp, toward the center of which are several papery almost circular seeds. David Fairchild, who studied this plant in Natal (its native home), writes of it: "On the markets of Durban the long, brilliant red fruit of the amatungula is commonly sold; in fact, during January and February it is one of the commonest fruits to be seen in the stalls. Though variable in size and shape, it has generally an elongated form, with a distinct point, and the diameter of a good-sized Damson plum. The thin red skin covers a pink flesh with a milky juice, which in flavor is sweet but lacks character, although much praised by European residents for use in making fruit salads."
The name under which this fruit is known in Natal is ama-tungula. In the United States it is called Natal-plum as well as carissa. The botanical name Arduina grandiflora, E. Mey., is a synonym of Carissa grandiflora.
In Florida, the carissa is not generally relished when eaten out of hand. When stewed it yields a sauce which greatly resembles that made from cranberries. It is also used for jelly and preserves. According to an analysis made in Hawaii by Alice R. Thompson, its chief chemical constituents are: Total solids 21.55 per cent, ash 0.43, acids 1.19, protein 0.56, total sugars 12.00, fat 1.03, and fiber 0.91.
The plant is not exacting in its climatic requirements. It will grow in warm, moist tropical regions, and in the dry subtropics wherever the temperature rarely falls below 26° or 28° above zero. In California it is sometimes injured by frost, but in southern Florida this is rarely the case. It succeeds on soils of varying types, red clay, sandy loam, and light sand. It is somewhat drought-resistant.
Fig. 57. The carissa (Carissa grandiflora) is a handsome shrub from South Africa, with fragrant white flowers and scarlet fruits whose flavor suggests raspberries. (X 1/2)
The carissa is particularly valued as a hedge plant. It withstands shearing admirably and its growth is compact and low. "To make an amatungula hedge," writes Fairchild, "is a very simple matter. The seeds are sown in a seed-bed, and when the young plants are six inches high they are transplanted to the place chosen for the hedge and set a foot apart, alternately in parallel rows, distant from one another a foot or more. As the plants grow they are trimmed into the desired hedge form, and the oftener they are trimmed the thicker they interweave their tough, thorny branches, making an impenetrable barrier for stock of all kinds. When in flower the white jasmine-like blossoms show off strikingly against the dark background of foliage; and the red fruit which follows is quite as pretty."
Cuttings, when planted directly after removal from the parent bush, do not form roots readily unless grown over bottom heat; but a method has been devised by Edward Simmonds at Miami, Florida, whereby nearly every one will grow. This consists in notching young branchlets while still attached to the plant, making a cut halfway through the stem 3 or 4 inches from the tip. The branchlet is then bent downward and allowed to hang limply until the end of the second month, when a callus will have formed on the cut portion, and the cutting may be removed and placed in sand under a lath shade, requiring another month to strike roots.
The carissa is also propagated by layering, and it is not difficult to bud, using the common method of shield-budding, essentially the same as practiced with the avocado. Late spring is the best time to do the work.
It has been noted in Florida and more particularly in California that many carissa plants are unproductive. This matter has never been fully investigated, but the preliminary studies of Allen M. Groves at Miami, Florida, suggest that the difficulty may be due to lack of the necessary insects to effect cross-pollination. It has been observed, however, that occasional plants uniformly bear heavily, and the vegetative propagation of such eliminates all danger of unproductiveness.
Plate XXIII. The jackfruit (Artocarpus integrifolia), the largest tropical fruit.
There are as yet no named varieties in the trade.
Another species of carissa, and one which is sometimes confused with C. grandiflora, is C. Arduina, Lam. (C. bispinosa, Desf., Arduina bispinosa, L.). This can be distinguished from C. grandiflora by the smaller size of the flowers, which are only \ inch broad in place of nearly 2 inches, with the corolla-segments much shorter than the tube; and by the oblong-obtuse fruit, which is only \ inch in length and contains one or two lanceolate seeds, instead of fifteen or twenty circular ones. The species is not commonly cultivated in the United States, but is said to be used as an ornamental plant in Cape Town, South Africa.
The karanda (Carissa Carandas, K. Sch.), a species common in India, has been introduced into the United States, but is not often planted either in California or Florida. It is distinguished from C. grandiflora and C. Arduina by the corolla-lobes being twisted to the right instead of to the left in the bud; by the oblong or elliptic-oblong leaves with rounded or obtuse tips; and by the spines being simple in place of bifurcate. Its fruits are less than an inch long, and contain three or four seeds. They are used in India for pickles and preserves.