Learning Objectives
The learner will be able to,
• Differentiate systematic botany from taxonomy.
• Explain the ICN principles and to discuss the codes of nomenclature.
• Compare the national and international herbaria.
• Appreciate the role of morphology, anatomy, cytology, DNA sequencing in relation to Taxonomy,
• Describe diagnostic features of families Fabaceae, Apocynaceae, Solanaceae, Euphorbiaceae, Musaceae and Liliaceae.
Chapter Outline
5.1 Taxonomy and Systematics
5.2 Taxonomic Hierarchy
5.3 Concept of species – Morphological, Biological and Phylogenetic
5.4 International Code of Botanical Nomenclature
5.5 Type concept
5.6 Taxonomic Aids
5.7 Botanical Gardens
5.8 Herbarium – Preparation and uses
5.9 Classification of Plants
5.10 Types of classification
5.11 Modern trends in taxonomy
5.12 Cladistics
5.13 Selected Families of Angiosperms
Plants are the prime companions of human beings in this universe. Plants are the source of food, energy, shelter, clothing, drugs, beverages, oxygen and the aesthetic environment. Taxonomic activity of human is not restricted to living organisms alone. Human beings learn to identify, describe, name and classify food, clothes, books, games, vehicles and other objects that they come across in their life. Every human being thus is a taxonomist from the cradle to the grave.
Taxonomy has witnessed various phases in its early history to the present day modernization. The need for knowledge on plants had been realized since human existence, a man started utilizing plants for food, shelter and as curative agent for ailments.
Theophrastus (372 – 287 BC), the Greek Philosopher known as “Father of Botany”. He named and described some 500 plants in his “De Historia Plantarum”. Later Dioscorides (62 – 127 AD), Greek physician, described and illustrated in his famous “Materia medica” and described about 600 medicinal plants. From 16th century onwards Europe has witnessed a major developments in the field of Taxonomy. Some of the key contributors include Andrea Caesalpino, John Ray, Tournefort, Jean Bauhin and Gaspard Bauhin. Linnaeus ‘Species Plantarum' (1753) laid strong foundation for the binomial nomenclature.
Taxonomy is no more classical morphology based discipline but become a dynamic and transdisciplinary subject, making use of many branches of botany such as Cell Biology, Physiology,Biochemistry, Ecology, Pharmacology and also Modern Biotechnology, Molecular Biology and Bioinformatics. It helps to understand biodiversity, wildlife, forest management of natural resources for sustainable use of plants and eco restoration.
5.1 Taxonomy and Systematics
The word taxonomy is derived from Greek words “taxis” (arrangement) and “nomos” (rules or laws). Davis and Heywood (1963) defined taxonomy as “the science dealing with the study of classification including the bases, principles, rules and procedures”. Though there were earlier usages of the term ‘systematics’, only during the latter half of 20th century ‘Systematics’ was recognized as a formal field of study. Simpson (1961) defined systematics as “Scientific study of the kinds and diversity
of organisms and all relationships among them”. Though there are two terms are used in an interchangeable way, they differ from each other.
5.2 Taxonomic Hierarchy
Taxonomic hierarchy was introduced by Carolus Linnaeus. It is the arrangement of various taxonomic levels in descending order starting from kingdom up to species.
Species is the lowest of classification and shows the high level of similarities among the organisms. For example, Helianthus annuus and Helianthus tuberosus. These two species differ in their morphology. Both of them are herbs but Helianthus tuberosus is a perennial herb.Genus consist of multiple species which have similar characters but differ from the species of another genus.Example: Helianthus, Tridax.Family comprises a number of genera which share some similarities among them. Example: Asteraceae. Order includes group of families which show less similarities among them. Class consists of group of orders which share few similarities.
Division is the next level of classification that consists of number of classes. Example: Magnoliophyta.
Kingdom is the highest level or rank of the classification. Example: Plantae
5.3 Concept of species-Morphological,Biological and Phylogenetic
Species is the fundamental unit of taxonomic classification. Greek philosopher Plato proposed concept of “eidos” or species and believed that all objects are shadows of the “eidos”. According to Stebbins (1977) species is the basic unit of evolutionary process.Species is a group of individual organisms which have the following characters.
1. A population of organisms which closely resemble each other more than the other population.
2. They descend from a common ancestor.
3. In sexually reproducing organisms,they interbreed freely in nature,producing fertile offspring.
4. In asexually reproducing organisms,they are identified by their morphological resemblance.
5. In case of fossil organisms, they are identified by the morphological and anatomical resemblance.
Species concepts can be classified into two general groups. Concept emphasizing process of evolution that maintains the species as a unit and that can result in evolutionary divergence and speciation.
Another concept emphasises the product of evolution in defining a species.
Types of Species
There are different types of species and they are as follows:
1. Process of evolution - Biological Species
2. Product of evolution - Morphological
Species and Phylogenetic Species
Morphological Species (Taxonomic species)
When the individuals are similar to one another in one or more features and different from other such groups, they are called morphological species. These species are defined and categorized with no knowledge of phylogenetic history, gene flow or detailed reproductive mechanisms.
Biological Species (Isolation Species)
According to Ernest Mayr 1963,“ these are groups of populations that interbreed and are reproductively isolated from other such groups in nature”.
Phylogenetic Species
This concept was developed by Meglitsch (1954), Simpson (1961) and Wiley (1978).Wiley defined phylogenetic species as “an evolutionary species is a single lineage of ancestor descendent populations which maintains its identity from other such lineages which has its own evolutionary tendencies and historical fate”.
5.4 International Code of Botanical Nomenclature
Assigning name for a plant is known as Nomenclature. This is based on the rules and recommendations of the International Code of Botanical Nomenclature. ICBN deals with the names of existing (living) and extinct (fossil) organisms. The elementary rule of naming of plants was first proposed by Linnaeus in 1737 and 1751 in his Philosophia Botanica.In 1813 a detailed set of rules regarding plant nomenclature was given by A.P. de Candolle in his famous work “Theorie elementaire de la botanique”. Then the present ICBN was evolved by following the same rules of Linnaeus, A.P. de Candolle and his son Alphonse de Candolle.
ICBN due to specific reasons and in order to separate plant kingdom from other organisms, is redesignated as ICN. The International Botanical Congress held in Melbourne in July 2011 brought this change. The ICN stands for International Code of Nomenclature for Algae, Fungi and Plants.
ICN Principles
International Code of Nomenclature is based on the following six principles.
1. Botanical nomenclature is independent of zoological and bacteriological nomenclature.
2. Application of names of taxonomic group is determined by means of nomenclatural types.
3. Nomenclature of a taxonomic group is based on priority of publication.
4. Each taxonomic group with a particular circumscription, position and rank can bear only one correct name, the earliest that is in accordance with the rules except in specified cases.
5. Scientific names of taxonomic groups are treated as Latin regardless of their derivation.
6. The rules of nomenclature are retroactive unless expressly limited.
