Plants, like animals, are classified or grouped into seven categories from the largest kingdom, to the smallest species. The unit of classification is the species, which groups individual plants with many similar features together. However, individuals of the same species are not identical.
The varieties of any species that may be presented are a consequence of the kind of soil it grows in; or the climate or the possible cross pollination it may have undergone. The chemical composition is the same for all varieties, though there may be differences in the concentration of active ingredients.
The great variety of plants in the vegetal world require a lot of ingenuity to classify and name them. This was a great problem for early botanists (plant scientists). Plants (the vegetal world) can be classified in three main ways:
1. There are three main ways of classifying plants, namely botanical, agricultural and based on the life cycle of the plants. In modern botanical classification, plants have three divisions, schizophytes, thallophtes and embryophtes. Agricultural classification is based on produce (food, fibre, latex, etc); and by life cycle as annuals, biennials and perennials, etc. Plants are still classified into four divisions: thallophyta, bryophyta, pteridophyta and spermatophyte.
2. Agricultural activities upset the ecosystem by destroying the vegetation, which insulates the soil; tillage or land preparation destroys the crumb structure of the soil and exposes it to soil erosion. The use of chemicals alters the soil pH, pollutes the surface water, and kills beneficial insects and other animals. The insecticide DDT is particularly dangerous and has been banned in some countries of the world.
3. Pests are the greatest enemies of agricultural production. If left uncontrolled, pests (especially insects: locusts, stem borers, beetles, weevils, etc.) can wipe out whole farms and there could be zero harvest. Herbicides are used to control weeds, while pesticides (which include insecticides) are used to control insect pests. Some pests are crop specific, e.g., the cocoa capsid. Many crop diseases are due to attack by viruses (mosaic), bacteria, protozoan and fungi, and through lesions left by rodents and beetles (yam beetles).
4. Sustained production of food is possible by improving crop yield, i.e., through good management of farm input, good and timely land preparation, good farm management and appropriate machinery. After food has been produced, a lot of wastage comes, inefficient harvest techniques, lack of holding capacity for the food produced and no good storage facilities. It is most important to preserve food, to have it all year round for consumption. Several techniques are used for storing food: from traditional cribs, improved cribs, silos and warehouses, all of which should consider ventilation, prevention of pest infestation and cost effectiveness.
5. Reproduction is the means of perpetuating the human species, but the rate of reproduction in the human race has resulted in human population that has become a threat to man’s future because of over-population. For the population to be sustained, there must be adequate food through improved crop yields, new farming techniques, good management and access to the source of food. Government and NGOs have to propose policies that ensure or aim at ensuring food supply.