Plants may also be classified based on the kind of crop or food they produce. The biological characteristics of plants are important to agriculture, because agricultural activities produce the food that supports the human population. On the basis of crop, plants may be classified as follows:
(i) Cereal or grain crops
a. Pulses and
b. Fodder (cover crop)
(iii) Root crops
(iv) Vegetable crops
(v) Beverages and stimulants
(vi) Tuber crops
(vii) Fruits and nuts
(viii) Latex crops
(ix) Wood crops
(x) Forage crops
(xii) Medicinal plants and drugs
(xiii) Fibre crops
(xiv) Oil crops
Cereal or grain crops
These plants are grown for their grains. They are grasses (Family gramineae). Examples:
Soya bean – Glycine max
Cowpea – Vigna unguiculata
Groundnut – Arachis hypogea
2. Fodder (cover crops): These are grown to suppress weeds. They are common legumes, e.g.
a. Centrosoma pubescens
b. Calapogonium muconoides
3. Root crops: These plants store most of their manufactured foods in the roots, e.g.
c. potatoes, etc.
4. Vegetable crops: Vegetable crops include the following:
a. Onions – Allium cepa
b. Carrots – Carrot letuea
c. Okra – Hibiscus esculentus
d. Melon – Citrullus vulgaris
e. Tomatoes – Lycopercon esculentus
f. Pumpkin – Telferia occidentalis
g. Water melon – Citrullus lunatus
5. Beverages and stimulants: These plants are the raw materials used for the manufacture of beverages, e.g., coffee and tea and drugs like opium (principally as a sedative in medicine), cocoa (theobroma cacao), kola (cola nitida), tea (cawellia seneinsis)
6. Tuber crops: These are swollen underground stems. The stems are food reserves that remain underground. Examples are tuberous roots of dahlia spp and cocoyam (xanthosoma sagitifolium).
7. Fruits and nuts: These plants produce edible fruits and nuts which are processed into various types of food items, especially for the fast food and soft drink industries.
8. Latex crops: These plants produce latex (a whitish liquid) when a branch, stem or leaf is cut The latex is economically important, because it is processed to give rubber which is used in the manufacture of tyres and tubes of the auto-industry.
9. Wood crops: These plants supply the timber requirements of the world. They produce wood to suit furniture manufacturers, boat builders, carving and craft and building materials. Soft wood is used in the pulp and paper industries. Example of timber: opepe, mahogany, black and white afara, etc.
10. Forage crops: These are food for animals especially grazers (cattle and sheep). They are mainly found among cover crops of legumes and grasses.
11. Ornamentals: These are beautiful plants that are used to beautify our surroundings. They are mainly flowers, beautiful shrubs, herbs and trees. There is a thriving business in cut roses in Jos, Plateau State.
12. Medicinal plant: These plants are mainly herbs, shrubs and twiners. These also have medicinal barks. The range of medicinal plants is very extensive from the tiny spirulina to the bark of an oak tree or the African walnut. These plants are known to have healing effects when mixed in concoctions and applied to the surface, or taken orally as remedies for various afflictions or diseases. Medicinal plants form the main raw materials for medicines prepared by herbalists and pharmaceutical companies. Well known examples of medicinal plants are garlic (Allium Sativium L) known to reduce blood pressure in man, and the sunflower, (Helianthus annuus L) which reduces excess cholesterol in blood. Students are strictly warned not to attempt to prepare concoctions from medicinal plants. Wrong preparation of medicines from plants could be dangerous.
13. Fibre crops: These are plants that produce fibres which are processed for the manufacture of bags (jute bags), ropes. and cotton for clothing. Examples are sisal hemp and jute.
14. Oil crops: Some plants have seeds and nuts that are rich in oil. This oil is easily extracted using a wide range of methods and machinery from manual to mechanical. Oils are processed into edible fat,lubricants, pomade, etc. Examples of such crops are shea nut, oil palm and sunflower
15. Spices: Spices are ingredients that may be present in small amounts but are important in flavouring our foods. These plants are grown specially for the spices harvested from them. Examples are peppers (Capsicum frutescers L.)