Kola is a member of the tropical family Sterculiaceae, and it grows as a tree form. Kola nuts from two species, Cola nitida and C. acuminata, have been important objects of trade for at least 1,000 years. These nuts are perhaps most well known now as a constituent of soft drinks.
There are over 50 species of kola. Of these seven have edible nuts, but only two have been commercially exploited (C. nitida and C. acuminata). The most important is C. nitida. The main centers of production are in Africa, particularly in Nigeria, Ghana, and the Ivory Coast. Annual production from these countries alone is in excess of 250,000 tons.
Generally, kola trees grow up to 40 ft (12 m) tall, although specimens in excess of 75 ft (25 m) are known. They produce small buttress roots and have a very dense foliage. The flowers are white or cream usually with red markings at the base. Two types of flower are produceda hermaphrodite flower with both male and female reproductive structures and a smaller male-only flower. They are quite similar in coloring, but are easily identifiable from a distance by their difference in size. The hermaphrodite flower is up to 3 in (7.5 cm) and the male flower is rarely above 1 in (2.5 cm). Insects, attracted by a particularly penetrating aroma, fertilize the flowers.
The seeds are produced as quite hard nuts. These can be of various colors but are all about 2-3 in (5-7.5 cm) long. Nuts are not produced by the tree until it is six or seven years old. Peak production does not start until the tree reaches 15 years of age. Estimates for the number of nuts produced annually per tree vary due to the age and location of the trees. However, a top figure of 120,000 nuts is often given. The nuts are generally produced between November and December for C. nitida and from April to July for C. acuminata.
It is believed that kola trees are native to Ghana and the Ivory Coast and that their spread has been brought about by humans. Kola trees were introduced to South America in the sixteenth century. This spread was brought about by the stimulating and sustaining properties of the kola nut. They grow best in tropical lowlands below about 600 ft (200 m). Kola trees are all evergreen, but they will start to shed their leaves at times of water shortage quite readily. The seeds will die if they are allowed to dry out, and they generally remain at the foot of the parent tree. In the wild this produces isolated groves of kola trees.
Even though everyone knows kola nuts from their use in soft drinks, they are present in these beverages only in minute quantities. In 8 gal (30 l) it is not uncommon to have less than 0.01 oz (0.4 g) of kola nut. The kola nut contains caffeine and theobromine. Caffeine is a mild stimulant and is widely used to wake people up, particularly when engaged in boring or repetitive tasks. Theobromine (which means food of the gods) is used in the treatment of coronary disease and headaches. The name kola comes from the eighteenth century and is probably a derivative of the West African kolo, the native name for the trees.
The commercial production of kola nuts is frequently carried out using clonal propagation. The plants thrive in half-shaded environments. Seed collection is still generally carried out manually in Africa, using hook-ended poles to cut the nuts down. Kola trees can be susceptible to attack by a number of species of fungi, and this becomes a major problem with the large scale farming that is now carried out. Insects can also cause great damage to kola trees. If the nuts are poorly stored, they may become infested with fungus or kola weevils.
The American Horticultural Society. The American Horticultural Society Encyclopedia of Plants and Flowers. New York: DK Publishing, 2002.
Heywood, Vernon H., ed. Flowering Plants of the World. New York: Oxford University Press, 1993.