Crops are plants which are cultivated by man for various uses, including food, and this chapter will be concerned with the classification of crops into different groups. Crops range from those which require elaborate and expensive production and processing methods, to the basic crops which are widely grown by small scale farmers. West Africa, has for many years, been an important source of food and raw materials used in European countries.
Crops can be classified in many different ways according to:
(a) their anatomy—monocotyledons and dicotyledons.
(b) their life cycle—annuals, biennials and perennials.
(c) their food values—cereals, tubers, legumes, vegetables, beverages etc. and
(d) their geographical distribution.
ANNUALS, BIENNIALS AND PERENNIALS
Classification here is based on life cycle. Within each of these three main groups further subdivisions can be made. Annuals — plants grown from seed which flower and seed within one season. Biennials — these are crops which require two seasons of growth to reach maturity. Perennials — plants that continue to grow and crop for more than one season
Annuals, Biennials and Perennial crops
Plants
Monocotyledons
- Annual (maize, rice, guinea corn, millet)
- Biennial (onion)
- Perennial (sisal, oil palm, sugar cane)
Dicotyledons
- Annual (tomato, okro, groundnuts)
- Biennial (cassava)
- Perennial (cocoa, rubber, coffee)
Annuals
These are crops which survive for only one season. They germinate, grow to maturity, flower, produce seed and die within one year. Most food crops are annuals but a few export or industrial crops also fall into this category. Examples are maize, rice, millet, cowpeas, yam and most vegetables.
Biennials
These are crops which require two seasons of growth to reach maturity. Vegetative growth takes place during the first year while growth in the second year is mainly concerned with the manufacture and storage of food, flowering and fruiting. Examples are cassava and cocoyam.
Perennials
These are plants which live for more than two season. Most perennial crops plants produce only vegetative growth during the first year. Flowering does not occur until the vegetative phase of growth has reached maturity. Herbaceous perennials normally flower in the second year of growth. Most tree crops are referred to as woody perennials. Once perennials begin to flower they produce flowers each season, if the conditions of their continued growth are suitable. Some perennials can live for 3–10 years such as pawpaw which is herbaceous perennial and woody perennial plants such as cocoa, rubber, oil palm can live for 30–80 years. The woody perennials are also known as permanent crops because of the number of years they can remain on the plots on which they are planted.
Diagram of a perennial crop
Classification based on Economic and Practical uses (food values)
Cereals
Belong to the family known as the Gramineae and are cultivated mainly for their seeds. They are by far the most important source of the world's food supply. Examples are maize, rice, guinea corn (sorghum) and millet. They are rich in starch and contains various amounts of protein.
Legumes
Provide a very rich source of protein. Apart from supplying protein for human consumption, also provide fodder crops for livestock. Help to enrich the soil by replenishing it with nitrogenous compounds produced as a result of nitrogen fixation. Examples are cowpea, groundnut, soyabean, pigeon pea, sword bean and bambara groundnut.
Root and Tuber crops
These are plants with edible roots and tubers. Examples include yams, cassava, sweet potatoes, and cocoyams. They are generally low in protein but high in carbohydrates. In raw form, contain a high percentage of water which is why they cannot be preserved for long periods.
Vegetables
Vegetables are very important in the diet of the people both as a source of minerals and as laxative. They are highly perishable, highly nutritious when used in the fresh form. It is a valuable supplement to the diet of town dwellers as they are also valuable sources of minerals. Important ones are okro, egg plants, onions, tomatoes, pumpkin, sweet melon, water melon, cucumber and carrots.
Fruits and Nuts
Most of these are perennial tree crops. Increasingly important ones are bananas, citrus, pineapples, guava, pawpaw, cashew and avocado pear. Cashew, coconut and walnut are among the important nuts cultivated across West Africa.
Beverages and Stimulants
Many of the beverage crops are perennial tree crops. Their refreshing and stimulating properties are due to the presence of small amounts of caffeine and related substances such as theobromine. A lot of foreign exchange is derived from these crops such as cocoa, coffee and kola. Tobacco is a stimulant crop grown for the basis of the manufacture of cigarettes, cigars and snuffs.
Spices
Many plants are used as spices and flavourings; many also have medicinal properties. Important crops in this category are ginger and peppers.
Oil crops
Vegetable oils are very useful for cooking in many homes and used in paints and varnish industries. Oils are used in lubrication as well as in the manufacture of soap and detergents. Oil palm, groundnut, coconut, and shea butter are oil producing crops.
Fibre
The discovery of synthetic material to replace natural fibre has led to a considerable reduction in the use of natural fibre for clothing. Nevertheless, cotton is still an important fibre crop. Other useful fibre crops are sisal and jute (kenaf).
Latex
Rubber is about the only crop plant of importance in this category. It is important in the manufacture of tyres, tubes, balls and rubberized shoes.
Ornamental Plants
These are plants that are used to add beauty to the surrounding of houses, schools, churches, hospitals and park. Ornamental plants are of these types:
(i) They are the herbs which usually possess brightly coloured and sweet-smelling flowers. Examples are Rose, Periwinkle, Sunflower and Marigold.
(ii) The shrubs usually possess colourful leaves and flower; they are very useful as hedges and boundary demarcation. Examples include Acalypha, Croton, Ixora, Hibiscus and Allamanda.
(iii) Ornamental trees are useful as shade plants around houses and in parks. Examples include Pride of Barbados, Acacia and Frangipany.
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