Pharmacognosy is closely related to botany and plant chemistry and indeed both originated from the earlier scientific studies on medicinal plants (Trease and Evans,2000)..
Pharmacognosy is concerned with the description and identification of drugs both in the whole state and in powder and with their history, commerce, collection, preparation and storage (Trease and Evans, 2000).
Although Pharmacognosy, is principally concerned with plant materials, there are a small member of animal products which are traditionally encompassed within the subject, these include such items as beeswax, gelatin, wool fat, vitamins, etc (Trease and Evans, 2000).
Pharmacognosy is derive from two Greek words “pharmakon” or drug and “gignosco” or knowledge (Trease and Evans, 2000).
The American society of Pharmacognosy defines pharmacognosy as “the study of the physical, chemical, biochemical and biological properties of drugs, drug substances or potential drugs or drug substances of natural origin.
A medicinal plant is any plant which, in one or more of its organs, contains substances that can be used for therapeutic purposes or which are precursors for the synthesis of useful drugs.
The WHO consultative group that formulated this definition stated also that such a description makes it possible to distinguish between medicinal plants whose therapeutic properties and constituents have been established scientifically, and plants that are regarded as medicinal but which have not yet been subjected to a thorough scientific study.
A number of plants have been used in traditional medicine for many years. Some do seem to work although there may not be sufficient scientific data (double-blind trials, for example) to confirm their efficacy. Such plants should qualify as medicinal plants. The term “crude drugs of natural or biological origin is used by pharmacists and pharmacologists to describe whole plants or parts of plants which have medicinal properties.
Plant materials continue to play an important role in the maintenance of human health since antiquity. Over 50% of all modern chemical drugs originated from natural plant sources. These plant products are the major source of drug development in pharmaceutical industry (Burton et al,1983).
Several plants are now being used in part or as a whole to treat many diseases. Active components of these plants are now being investigated, extracted and developed into drugs with little or no negative effect or contraindication (Oluyemi et al,2007).
Rural dwellers in most part of the world do not depend on the orthodox medicine for the cure of diseases and ailments. This is because most of the modern equipment are expensive and service delivery too expensive to afford (Sofowora, 2003).
As a result of this, a larger section has resulted to the use of traditional medicine which are believe to be less expensive (Sofowora,2003).
This initial identification of more than 20,000 species of medicinal plants of tropical forests origins by the World Health Organisation, in 1978 has contributed immensely to our knowledge of different uses of plants most of these plants have their present uses rooted in traditional medicines which plays a major part in maintaining the health and welfare of both rural and urban dwellers in developing countries (Oyesola, 2007).
Natural products have been and have remained the cornerstone of health care present estimates show that, 80% of the world’s population still rely on traditional medicine for their health care needs.
Foliage leaves vary greatly in their internal structure and the difference are related to taxonomic grouping and to evolutionary adaptations of plants to different habitats.
Ebukanson and Bassey, 1992 defines stomata as apertures in the epidermis of leaves, herbaceous stems and floral parts surrounded by two specialized kidney shaped epidermal cells known as guard cells. Stomata are usually found in leaves and occur either in one or both surfaces but are most common on the abaxial surface.
For leaves in particular, the shape of the epidermal cells in surface view, the nature and distribution of the wall thickening, the presence or absence of cuticle and its form, the distribution and structure of the stomata, the presence or absence of well differentiated subsidiary cells to the stomata the presence of characteristic cell inclusions such as cystoliths, the presence or absence and form, size and distribution of epidermal trichomes and the presence and distribution of water-pores should all be carefully noted in describing the characters of an epidermis (Trease and Evans, 1989).
The structures of the epidermis and stomata are of first importance in the microscopical identification of leaves (Trease and Evans, 2003).
Three main types of stomata are distinguishable, the anisocytic (formerly cruciferous) type, with the stoma surrounded by three or four subsidiary cells, one of which is markedly smaller than the others, the paracytic (formerly rubiaceous) type with two subsidiary cells with their long axes parallel to the pore and the diacytic (formerly caryophymaceous) type with their long axes at right angles to the pore of the stomata (Trease and Evans, 2000).
The density of stomata has been established as 100 – 300 per square millimeter for leaves of many species (Metcalfe and Chalk, 1979). The abonormalities of stoma are as follows:
According to Esau (1965) examination of the epidermis in surface view shows that there are wide variations in the sizes of stomata as well as in the frequency and distribution. All unicellular and multicellular appendages of the epidermis are designated by the term trichomes. The hairs or the trichomes are used in classifying the genera and species (Metcalfe and Chalk, 1979).
According to Trease and Evans, the epidermis of the root constitute the piliferous layer and that of the shoot is a highly differentiated and compact layer of cells.
The compositae is the largest family of flowering plants and contains about 900 genera and some 13,000 species. Compared with some other large families such as leguminosae, the number of important economic products derived from it is relatively small (Trease and Evans, 2000).
The two subfamilies and their main genera are as follows:
Characteristics of Tubuliflorae
Characteristics of Liguliflorae
Hieracium (over 1000spp) Trease and Evans, 2000).
1.2 AIMS AND OBJECTIVE
The aim of this work is to study the Pharmacognostic properties on the leaves of Aspilia africana. These include the qualitative microscopy and quantitative microscopy.
Qualitative Microscopy: This involves the microscopical examination of the leaves of Aspilia africana. In qualitative microscopy to find out.
1.3 SIGNIFICANCE OF THE STUDY
The result of this study will have implications for improvement of the diagnostic features of Aspilia africana(Pers) C. D. Adams for the identification and preparation of a monograph on the plant and also the features will be valuable at the level where classical methods of cytology and genetics cannot be applied.