Cola spp., family Sterculiaceae
Several species of Cola are cultivated for the kolanut. Purseglove (1969*) listed four cultivated species, but van Eijnatten (1969) stated that only two were of commercial significance: (C. nitida (Vent.) Schott & Endl., which is the main kola of commerce, and C. acuminata (Beauv.) Schott & Endl.). The kolanut is native to Africa, with Nigeria the primary producing country. An estimated 140,000 tons were produced in 1960 mostly in Nigeria. This would indicate that something like one-half million acres were involved. A few hundred tons are exported to the United States, where they are used in the preparation of beverages and in pharmaceuticals. In Africa, the kolanut is chewed for its alkaloid properties (caffeine, kolanin, and theobromin), which dispel sleep, thirst, and hunger. There seems to be a slight preference for white kolanuts over red ones.
For the above and subsequent discussion, see van Eijnatten (1969) and Russell (1955a, b).
The kola tree is a dome-shaped evergreen tree, usually 35 to 50 feet in height. Trees are usually planted from seed, about 20 to 27 feet apart, although vegetative production can be accomplished. Growth of this tropical tree is in flushes. Flowering begins at 6 to 10 years. The fruit matures about 41/2 months after flowering. Full fruit production is reached by the 20th year, and the tree may continue bearing until it is 70 to 100 years old. The main harvest period of nuts extends from October to December, but some nuts may be available throughout the year. The pod is harvested before the nuts are ripe. The follicle is split and the three to six nuts are removed, fermented in heaps for 5 days, washed clean, and stored. They will keep for several months. Average yield is 210 to 250 salable nuts per tree or 12,000 nuts (about 500 pounds) per acre.
The fetid kola flowers are in several- to many flowered determinate panicles. The five-sepal, petalless flower is white, with maroon to reddish blotches and streaks emanating from the inner base of the corolla-like perianth. Some trees produce only male flowers, but some hermaphrodite flowers are usually on every tree. Usually, the earliest flowers to develop are male; followed by both male and hermaphrodite flowers intermixed. The hermaphrodite flower is 30 to 40 mm across; the male flower, half to two-thirds the size. The male flower is subspherical, the hermaphrodite one is more oval. The hermaphrodite flower produces pollen that will germinate on a proper agar solution but will not fertilize a stigma, so the flower is basically nonfunctional, and should be considered as a pistillate one.
The hermaphrodite flower opens between 4 and 8 a.m. and is apparently receptive only one day, as the majority wither and drop on the second to the fourth day. Naturally, all male flowers shed. When the flower opens, the anthers dehisce a sticky pollen, which largely remains on the anthers. This would indicate that the kola flower is insect pollinated. No reference was found indicating that kola flowers secrete nectar, but since flies are attracted to the flowers quite probably nectar is secreted.
The evidence indicates that pollen must be transferred from the staminate or male flowers to the hermaphrodite or basically female flowers. The pollen must be transferred as soon as possible after the flower opens. Many trees, and probably the majority of them, are self- incompatible, in which case the pollen must come from flowers of other appropriate kola trees.
Considering the large number of flowers on a tree that must set fruit to produce an excellent crop, and considering that the pollen must come from other compatible plants and within a limited time period, it becomes evident that pollen must be transported rather freely between trees.
The pollen of kola trees is not wind transported. Van Eijnatten (1969) said that pollination is probably affected by insects, but indicated that relatively few insects visit the numerous flowers. Purseglove (1968*) stated that the flowers have a fetid odor that attracts flies, which may be the pollinating agent. Cecidomyids, mirids, and ants have also been mentioned (Anonymous 1957). Nothing is said about bee visitation to these flowers. It is of interest that this is a relatively self- sterile crop, and van Eijnatten (1969) stated that, "The low productivity of many kola trees has been a thorn in the flesh of the farmer wherever this crop is cultivated in West Africa." The saturation pollination with one to several honey bee colonies per acre, forcing the bees to forage on what may be a relatively unattractive source of pollen or nectar, might remove that objectionable "thorn in the flesh." It might lift total production to a new plateau or cause a more concentrated set of fruit at a definite period.
Van Eijnatten (1969) stated that controlled pollination, apparently referring to hand pollination, could increase the yield ten- to twentyfold. This should appear to be sufficient incentive for the kolanut industry to explore the utilization of honey bees or other bees in the pollination of this crop.
EIJNATTEN, C. L. M. VAN.
RUSSELL, T. A.
______ 1955b. THE KOLA NUT OF NIGERIA AND THE CAMEROONS. Trop. Agr. [Trinidad.] 32: 210 - 241.
Source: Agricultural Research Service