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CONCEPT OF TAXONOMY ON HIGH PLANTS
BI -213: Taxonomy of Higher Plants CHAPTER- I INTRODUCTION TO PLANT TAXONOMY. BY PHILIPO REVOCATUS ___________________________________________________________________________ TAXONOMY is one of the oldest fields of the biology with a long history of development. The primeval people were using the plants for their food, shelter and medicine. This dependency urged even the primitive man to identify plants and also classify them into different groups such as food plants, medicinal plants and poisonous plants etc. This forms the basic tool for the classification of plants. This basic tool was used from one generation to the next. Ultimately the basic recognition of grouping of plants has evolved a highly complex scientific branch which with full development is known as taxonomy. DEFINITION: Taxonomy is the branch of biological science which is concerned with identification, nomenclature and classification in a system made up according to the available evidence of phylogenetic relationships. The word Taxonomy was first used by the French botanist A. P. de Candolle in 1813, in his book            “ Theorie Elementarie de la botanique”. It means lawful arrangement of objects into groups and is derived from two Greek words (Taxis = arrangement; nomous = law or rule ). Thus taxonomy means classification following certain rules or principles. Taxonomy is frequently used synonymously with the term “systematic Botany” or “Systematics”. However, Systematics is defined as the study of the diversity and the history of organisms and the evolutionary relationships between them. In short, systematics may be defined as the “the science of organisnal diversity”. It is based on the underlying assumption that evolution occurred in the past and it is continuing today. OBJECTIVES OF PLANT TAXONOMY The main objectives of taxonomy are to gather knowledge of the different kinds of plants in universe other names and of their systematic groupings. The flora of the universe is so large and it is not possible to gain knowledge without arranging systematically. The collection of plants and their study in form of herbarium is the first objective of taxonomy. This includes naming of plants, their distinctions, distribution, habitat characteristics and correction. 2. The second objective is to provide a method for identification and communication. The method of identification is accomplished by producing descriptions, keys, illustrations etc. The communication is done by publishing floras to account for the plants of a given area and manuals are prepared for ready identification. 3. The third objective is to prepare universal system of classification. To classify plants it is desirable to know the basic units of classification, the resemblance of plants in morphological characters and to have knowledge about phylogenitic relationships. The diversity of the plant world creates problem in understanding evolution. The universally accepted classification is not easily available but the data of variation and diversity with other phylogenetic considerations, as more or less universally accepted classification may be possible. FUNCTIONS OF TAXONOMY: Taxonomy has the following three basic functions viz., 1.	Identification, 2.	Nomenclature and 3.	 Classification.

1.	IDENTIFICATION Identification is the determination of a plant as being identical to or different from a previously known plant. Proper and correct identification of a taxon is a prerequisite for any study based on it. The identification is based on overall similarities and dissimilarities with an already known taxon. Identification is generally done by comparing the characters of the plant with an authentic herbarium specimen or indirectly with the help of literature. Generally the characters derived from grass morphology are sufficient for provisional determination. In case, the specimen in question does not agree or compare with existing predetermined specimen, it is taken to be a new to the science. This is the most exciting situation for a taxonomist to discover a ‘new’ taxon. Floras, monographs, manuals and journals are important sources of literature. The modern method is the use of computer punch card keys. Royal Botanical Gardens at KEW in ENGLAND has the largest herbarium and is an international centre for plant identification. It regularly publishes Index Kewensis (IK) for reference, and that aims to register all botanical names for seed plants at the rank of species and genera. It later came to include names of taxonomic families and ranks below that of species. The National Herbarium of Tanzania (NHT) helps in the identification of plants in our country.

THE NATIONAL HERBARIUM OF TANZANIA (NHT), ARUSHA The National Herbarium of Tanzania is a division of the Technical Services Department of Tropical Pesticides Research Institute (TPRI). NHT was established under the TPRI Act of 1979 with the mandate of cataloguing the entire flora of Tanzania and recording the resultant information for easy access by the general public and other institutions. NHT's vision is to conserve and preserve plant diversity and promote the sustainable utilization of plants. To this end, NHT undertakes many activities, some of which are collecting and curating botanical specimens, offering courses on herbarium techniques, producing plant checklists and publications, and building a computerised database of local plants. All these efforts are in furtherance of NHT's overarching objectives, which include botanical and other plant-related research, collecting and identifying specimens of locally occurring plants, preserving collected specimens in permanent reference collections, advising individuals, institutions, and government on utilization and conservation issues, and strengthening local and international collaboration in botanical activities. 2.	NOMENCLATURE Providing a correct scientific name to an identified plant is called nomenclature. It is necessary for proper communication and identification of taxa. A plant may be known with different common names in different parts of the world in different languages. Sometimes different plants may have common name. In some cases, there may be more than one common name for the same plant in the same language in different regions. Such situations lead to a lot of confusion. In order to avoid such confusions, a universally acceptable name becomes necessary. For this, there are international rules given in the International Code of Botanical Nomenclaturen (ICBN) which directs the process to be followed for the determination of the name applied to a particular plant. The basic rule is that binomial nomenclature should be followed for naming all plants. This means that each plant must have two names – the first is the generic name and the second is the specific epithet. i.	BINOMIAL NOMENCLATURE: The earliest scientific names of plants were ‘polynomials’ in which several Latin words were used giving the description of the plant. Subsequently Gaspard Bauhin (1623) used only two words for the first time and introduced the binomial system. However, the credit of using binomial system consistently for the first time in his ‘Species Plantarium’ goes to Carolus Von Linnaeus (1753). In binomial system every plant name will have two words and invariably they should be in Latin. The first word will be the name of the genus and the second word will be the name of the species. The generic name will be in the noun form and always begins with CAPITAL LETTER. The specific name will be in the adjective form and starts with small letter. For example Solanum tuberosum is the name of potato plant in which Solanum is the genus and tuberosum is the species. ii. INTERNATIONAL CODE OF BOTANICAL NOMENCLATURE (ICBN): Naming of all plants should be done in accordance with the principles laid down by ICBN. These rules are framed at the periodical meetings of International Botanical Congress held once in five or ten years. The 1st meeting was held at Paris in 1867 which resulted in PARIS CODE. The latest meeting was held at Vienna (XVII – International Botanical Congress- 2005), which results the Vienna Code-2006. According to the ‘ICBN’ the following rules must be followed while naming the plants. 1.	Every plant should have only ONE correct name. 2.	The scientific name must be in Latin. 3.	Binomial Nomenclature system must be used for naming the plants. 4.	The scientific name should be either underlined or published in italics. 5.	The author’s name may be given in abbreviated form at the end of scientific name. Eg. Pisum sativum L. (‘L’ stands for Linnaeus). 6.	If the generic name and the specific name are exactly the same it is known as tautonymy. According to ‘ICBN’ tautonyms are not valid in plant nomenclature. Eg. Malus malus.

3.	CLASSIFICATION Assigning the plants to specific groups on the basis of their similarities or dissimilarities is called classification. Keeping in view of the enormous number of species of plants on this earth, it is impossible to study them individually. And thus, it becomes necessary to study them in an organised manner and place them into large or small groups based on their similarities. These groups, the taxa are then arranged in a sequential order into categories according to their rank. Each taxa is given a following the rules of nomenclature. “Species” is the basic unit. The similar plants are grouped under ‘species’. Different species with related characters are grouped into one genus. Different genera with common characters are grouped into a family and so on in sequence of increasing inclusiveness. Thus, classification is an arrangement of plants into a hierarchy of ranks or categories. Different Systems of Classifications: Starting from Theophrastus (340 BC) who is known as Father of Botany to present day, several taxonomists have proposed different systems of classification based on different criteria. On the basis of the different criteria taken into account, all these systems can be grouped into three types, they are: i.	Artificial Systems ii. Natural Systems and iii. Phylogenetic Systems i.	Artificial Classifications: The earlier systems of classification were purely artificial. In these classification systems the plants are classified by means of one or very few easily observable, comparable and constant characters like morphology, natural habits etc. Eg. 1. Classification of plants on the basis of form into herbs, shrubs, trees etc. By Theophrastus in his book, Historia Plantarum is an artificial system. Eg. 2. Sexual system of classification proposed by Linnaeus, divided the plant kingdom in to 24 classes and 87 orders depending on the number, nature of stamens and carpels or on other characters of stamens. In this system the names of the classes and orders indicate the nature of androecium and gynoecium for the first time. As Linnaeus made use of morphological nature of stamens and carpels mainly to classify the plants. ii. Natural Classifications: Pre-Darwinian systems are mostly natural. They are based on over all similarity, mostly in gross morphology. Natural systems are based on the dogma of Constancy of Species i.e. Species are created specially by God and they do not undergo changes. Eg. The classification proposed by Bentham and Hooker is a natural one. Usage of morphological characters in delimiting the overall similarity, the concept used in 18th and 19th century, has undergone considerable refinement in recent years. Now overall similarity is judged on the basis of the features derived from all available fields of taxonomic information i.e. phonetic relationship. Classification based on phonetic relationship utilises data from morphology, anatomy, embryology, ultra structure, phytochemistry and many other fields of embryology. iii. Phylogenetic Classifications: These are the systems proposed after the publication of “Origin of Species” and the announcement of ‘Theory of evolution’ by Charles Darwin (1859). Hence they are called Post-Darwinian Classifications. They reflect the genetic and evolutionary relationships among the taxa and show them in the form of a phylogenetic tree or cladogram. Eg. Classifications made by Eichler, Engler and Prantal, Rendle, Bessy, Hutchinson and others come under this category. More recent classifications made by Conquist, Goldberg, Thorne, Armen Takhtajan have used data from different branches of botany apart from vegetative and floral characters. UNITS OF CLASSIFICATION Living organisms exhibit different degrees of diversity. The entire diversity cannot be classified into one group. Hence we recognize different taxonomic groups depending upon different levels of diversity. The different levels of groups so proposed are recognized as a series of hierarchical categories. Irrespective of its rank in the sequence, every unit is called a ‘TAXON’. ‘Species’ is the basic unit of classification. All those plants which are identical in all respects are regarded as one species. Different species with related characters are grouped into one ‘genus’. Different genera with common characters are grouped into a ‘family’. Closely related families are grouped into an ‘order’. Different orders which are related to each other are grouped into a ‘series’. A group of related series is considered as a class. Different classes with similarities are grouped into a ‘Division’. A group of divisions constitute the “KINGDOM” which is the largest taxon occupying the top most position in the taxonomic hierarchy. Intermediate sub groups are also recognised and intra specific categories are also known.

Systematic position of Baobab tree (Swa: Mbuyu) is as follows (according to Benthem & Hooker’s classification system) Taxonomic Category	Taxonomic Group Kingdom	Plantae Division	Phanerogamae Sub division	Angiospermae Class	Dicotyledoneae Sub class	Polypetalae Series	Thalamiflorae Order	Malvales Family	Bombacaceae Genus	Adansonia Species	digitata

The names applied to classes are in ‘Latin’ and have the ending ‘eae’. Eg. Monocotyledoneae and Dicotyledoneae. The name of ‘order’ ends with the suffix ‘ales’, although the ending ‘ae’ is permissible in some Eg. Rubiaflorae, Glumiflorae, Farinosae etc. Examples of ‘ales’ ending are Ranales, Malvales, Parietales etc. Very large orders are divided into suborders. The conventional ending of sub-orders is ‘nieae’. Eg. Potamogetonieae and Alismatinieae. Order (or suborder) is further divided into families. The customary ending of family is – ‘aceae’. Eg. Malvaceae. PRINCIPLES OF PHYLOGENETIC CLASSIFICATION The principal aim of plant taxonomy is to provide a system of classification based on evolutionary relationships. Most of the earlier systems of plant classifications are based on exomorphic characters, placing emphasis on floral structure. After the publication of Charles Darwin’s Origin of Species in 1859, attempts have been made to classify plants on their phylogenetic relationships. However, there is no general agreement among the taxonomists, as to the true nature of primitive and advanced character of taxa. Charles E. Bessy for the first time proposed a set of dicta (rules) based on empherical evidence, to distinguish between primitive and advanced features. These rules were later refined by Hutchinson, Rendle, Takhtajan and others. General principles adopted for the classification of flowering plants: 1.	Evolution is both upwards and downwards. 2.	Evolution does not necessarily involve all organs of the plant at the same time. 3.	Evolution has generally been consistent. PRIMITIVE AND ADVANCED CHARACTERS: Primitive Characters	Advanced Characters Principles relating to the general habit: 1	Trees and Shrubs	Herbs and Climbers 2	Perennials	Biennials and anuals 3	Terrestrial Plants	Aquatic Phanerogames, Epiphytes, Saprophytes, Parasites. Principles relating to the general structure of flowering plants: 4	Stems with collateral vascular bundles in whorls	Stems with scattered vascular bundles 5	Spiral phyllotaxy	Opposite and whorled leaves 6	Simple leaves	Compound leaves Principles relating to the flowers and fruits: 7	Bisexual flowers	Unisexual flowers 8	Monoecious condition	Dioecious condition 9	Solitary flower	Inflorescence; the highest forms are Umbel and Capitulum 10	Spirally arranged floral parts	Floral parts in whorls (cyclic flowers) 11	Floral parts several	Floral parts few in number 12	Flowers with petals 	Flowers naked by reduction 13	Polypetalous corolla 	Gamopetalous corolla 14	Twisted corolla	Imbricate and Valvate corolla 15	Actinomorphic flower	Zygomorphic flower 16	Hypogyny, Perigyny	Epigyny 17	Many carpels, free condition	Few carpels, united condition 18	Endospermic seed with small embryo	Non-endospermic seed with large embryo 19	Numerous stamens	Few stamens 20	Free stamens	United stamens (adelphy or syngenesious) 21	Simple fruit	Aggregate fruit 22	Capsule	Drupe and Berry 23	Chlorophyll present	Chlorophyll absent (parasites and saprophytes) 24	Evergreen	Deciduous