Diversity of Seed Plants and Their Systematics
Angiosperms II (Nomenclature, Classification with emphasis on Bentam and Hooker and Engler and Prantl, Taxonomic evidence – Role of Cytology, Phytochemistry and Taximetrics)
M.P. Sharma
Reader
Department of Botany
Jamia Hamdard
Hamdard Nagar
New Delhi - 110062
Date of submission: February 14, 2006
Significant keywords: Taxonomy, Angiosperms, Classification, Systematics, Nomenclature, Taxonomic evidence.
M.P. Sharma
Reader
Department of Botany
Jamia Hamdard
Hamdard Nagar
New Delhi - 110062
Date of submission: February 14, 2006
Significant keywords: Taxonomy, Angiosperms, Classification, Systematics, Nomenclature, Taxonomic evidence.
Classification Of Angiosperms
Keeping the things arranged is a basic human instinct. Laboratories, libraries workshops, shops etc are easier to work in if there is a system to keep track of things. Biology is no exception. It is lot easier to study living things if we have a system that keep something apart from other things. Biologists called this system as classification or taxonomy. Typically, classification can be defined as the systematic arrangement of similar organisms into categories on the basis of their structural or evolutionary relationships.
The naming and classification of plants undoubtedly began in the earliest stages of civilization. Our own observations show that plants are of many kinds, and we immediately seek for a name to apply to a plant of interest. The primitive people and tribal communities of today, as well in the past, apply common names to those plants that are peculiar or that affect their life in any way. Early classification systems were utilitarian; plants were grouped as to whether they were beneficial or harmful.
With increasing civilization, especially as knowledge grew concerning the uses of plants in food and medicine, the necessity of plant names became even greater. And ultimately, as the number of known plants increased and as botanists collected plants from far corners of the earth, it became necessary to group plants into large categories following rational principles. The collection, naming and classification of plants nowadays are carried out mainly with the objective of showing their origins and relationship, and also to provide positive identification for the hundreds of thousands of different kinds of plants.
The naming and classification of plants undoubtedly began in the earliest stages of civilization. Our own observations show that plants are of many kinds, and we immediately seek for a name to apply to a plant of interest. The primitive people and tribal communities of today, as well in the past, apply common names to those plants that are peculiar or that affect their life in any way. Early classification systems were utilitarian; plants were grouped as to whether they were beneficial or harmful.
With increasing civilization, especially as knowledge grew concerning the uses of plants in food and medicine, the necessity of plant names became even greater. And ultimately, as the number of known plants increased and as botanists collected plants from far corners of the earth, it became necessary to group plants into large categories following rational principles. The collection, naming and classification of plants nowadays are carried out mainly with the objective of showing their origins and relationship, and also to provide positive identification for the hundreds of thousands of different kinds of plants.
Kinds of Classification
According to the principle employed, mainly three kinds of classifications are recognized. They are: Artificial, Natural and Phylogenetic. In practice, these may overlap.
Artificial Classification is based on convenient or conspicuous diagnostic characters without attention to characters indicating relationship; often a classification based on a single arbitrarily chosen character such as flower colour, habit, habitat, time of flowering or arrangement of leaves, rather than an evaluation of the totality of characters. The earlier pre-Darwinian systems of classification were largely artificial. Linnaeus’ sexual system, which is based on the number of stamen and pistils, falls in this category since unrelated plants can have same number of stamen and pistils in their flowers.
Natural Classification is one which is based on over-all resemblances in external morphology, and unlike artificial systems, involved as many characters as possible. It is presumed that the larger the number of characters shared by different plants, more closely are they related to each other. Overall gathering data from diverse disciplines like palynology, embryology, anatomy, phytochemistry, cytology etc, and not the morphology alone nowadays ascertain similarity. Later pre-Darwinian systems, which were based on over-all resemblances in gross morphology, were mostly natural.
Phylogenetic Classification is based on hypothesized evolutionary relationship. In the years, following Darwin’s Origin of Species (1859) the theory of evolution gradually replaced the concept of special creation of species. It was found that species are not fixed or unchanging, but have evolved from pre-existing species during geological time. It is now considered that, in general, similarities in structure are evidences of evolutionary relationship. Thus have arisen modern phylogenetic systems of classification based on relationship by descent. Such systems utilize previously determined natural groups, and categories – genera, family, orders – of the natural systems are arranged in scheme that presumably reflects evolutionary relationships. Since 1980’s phylogenetic classification has been made much more facile by using molecular data. Data from many sources are used to determine relationship. Thus any phylogenetic scheme of plant classification is subject to change as our knowledge of the various groups increased.
History and Development of Plant Classification
In order to understand the field of taxonomy or classification at the present day, it is necessary to have some knowledge of the history of the subject and the development of the ideas associated with it. The observations made by the earlier workers were never wasted; subsequent workers with some modifications incorporated them into classifications. Scientists have struggled to find correct classification systems to use. They have eventually agreed on the systems we use today.
Artificial Classification is based on convenient or conspicuous diagnostic characters without attention to characters indicating relationship; often a classification based on a single arbitrarily chosen character such as flower colour, habit, habitat, time of flowering or arrangement of leaves, rather than an evaluation of the totality of characters. The earlier pre-Darwinian systems of classification were largely artificial. Linnaeus’ sexual system, which is based on the number of stamen and pistils, falls in this category since unrelated plants can have same number of stamen and pistils in their flowers.
Natural Classification is one which is based on over-all resemblances in external morphology, and unlike artificial systems, involved as many characters as possible. It is presumed that the larger the number of characters shared by different plants, more closely are they related to each other. Overall gathering data from diverse disciplines like palynology, embryology, anatomy, phytochemistry, cytology etc, and not the morphology alone nowadays ascertain similarity. Later pre-Darwinian systems, which were based on over-all resemblances in gross morphology, were mostly natural.
Phylogenetic Classification is based on hypothesized evolutionary relationship. In the years, following Darwin’s Origin of Species (1859) the theory of evolution gradually replaced the concept of special creation of species. It was found that species are not fixed or unchanging, but have evolved from pre-existing species during geological time. It is now considered that, in general, similarities in structure are evidences of evolutionary relationship. Thus have arisen modern phylogenetic systems of classification based on relationship by descent. Such systems utilize previously determined natural groups, and categories – genera, family, orders – of the natural systems are arranged in scheme that presumably reflects evolutionary relationships. Since 1980’s phylogenetic classification has been made much more facile by using molecular data. Data from many sources are used to determine relationship. Thus any phylogenetic scheme of plant classification is subject to change as our knowledge of the various groups increased.
History and Development of Plant Classification
In order to understand the field of taxonomy or classification at the present day, it is necessary to have some knowledge of the history of the subject and the development of the ideas associated with it. The observations made by the earlier workers were never wasted; subsequent workers with some modifications incorporated them into classifications. Scientists have struggled to find correct classification systems to use. They have eventually agreed on the systems we use today.
The discipline of plant classification has extremely deep cultural roots in all parts of the world. Ancient men who made their living by gathering food from the wild were probably much more familiar with the local plants, in terms of species recognition, than most people today. Though several cultural groups like African, Asian and Native American carried a wealth of botanical information into modern times, present systems of angiosperm classification have been derived from a European base. Historical development of classification is briefly reviewed here.
The Ancients
Theophrastus (370 – 285 B.C.). He was a Greek philosopher and is regarded as the “Father of Botany”. He was born in the city of Eresus. A people of Plato, and later a people and assistant to Aristotle, he embodied to the full extent the culture and learning of ancient Greece. For most of his life he lived in the midst of Lyceum botanical garden, established by Aristotle at Athens, and there he taught and wrote books representing many fields of knowledge. Theophrastus covered most aspects of botany: description of plants, distribution, classification, propagation, germination and cultivation. He is accredited with more than 200 publications; only few of his writings survive today. His two important botanical works “Inquiry into Plants” and “The causes of Plants” provided a systematic treatment of over 500 species according to habit (herbs, under-shrubs, shrubs and trees) and separated according to flowering and non-flowering. He recognized and described families among flowering plants, such as carrot family, known today as Umbelliferae (Apiaceae). He recognized genera, in the sense of a group of species, and applied to them Greek names then in use. A few generic names currently in use, such as Daucas, Asperagus, Anemone, and Narcissus, originated during his time.
Dioscorides ( Ist century A.D. ) was a Greek physician in Roman army. His most famous work was De Materia Medica, which discussed the medicinal qualities of 600 plants. This included natural grouping of species that represent well-defined modern families (Apiaceae, Fabaceae, Lamiaceae). The plant descriptions in his De Materia Medica were adequate for identification, including methods of preparation, medicinal uses, and doses. His work was used in various translations and editions for next 1000 years.
The Middle Or Dark Ages
The period from the fall of the Rome to the Renaissance is often called dark ages because of intellectual stagnation. Very little original botanical work was done during this period. Most workers copied and translated the ancient work of Greeks and Roman.
Alburtus Magnus (1193-1280 A.D.) was only botanist of note during this period. His contemporaries popularly called him “Doctor Universalis”. In his work De Vegetabilis he is believed to have first differentiated monocots from dicots.
RENAISSANCE, THE HERBALISTS AND TRANSITION PERIOD
Gerome Bock (1469-1554). German. Neu Kreuterbuch.
Leonhard Fuchs(1501-1556). German. De Historia Stirpiu, New Kreuterbuch.
John Gerard (1542-1612). English. The Herball,or, Generall Historie of Plantes.
Rombert Dodoens (1517-1585). Flemish. Cruydeboeck.
Dioscorides ( Ist century A.D. ) was a Greek physician in Roman army. His most famous work was De Materia Medica, which discussed the medicinal qualities of 600 plants. This included natural grouping of species that represent well-defined modern families (Apiaceae, Fabaceae, Lamiaceae). The plant descriptions in his De Materia Medica were adequate for identification, including methods of preparation, medicinal uses, and doses. His work was used in various translations and editions for next 1000 years.
The Middle Or Dark Ages
The period from the fall of the Rome to the Renaissance is often called dark ages because of intellectual stagnation. Very little original botanical work was done during this period. Most workers copied and translated the ancient work of Greeks and Roman.
Alburtus Magnus (1193-1280 A.D.) was only botanist of note during this period. His contemporaries popularly called him “Doctor Universalis”. In his work De Vegetabilis he is believed to have first differentiated monocots from dicots.
RENAISSANCE, THE HERBALISTS AND TRANSITION PERIOD
The renaissance in Europe that started in the 14th century marked the beginning of an active period in which artistic, social, scientific, and political thoughts turned into new directions. Two major technological innovations – printing press and science of navigation – contributed to renaissance and especially to plant taxonomy. With the invention of printing press in 1440, many large volumes about plants and their medicinal uses, known as herbals, were produced throughout Europe. The authors of these books (herbals) are known as ‘herbalists’. It helped making knowledge available about the practical uses of plants, primarily from medicinal standpoint, to all. Herbalists did not propose any original systems of classification but marked the period of original work rather than copying the ancient work. Navigation made explorations easy and the collection of new species from ongoing explorations forced the herbalist to extend the initial efforts of the ancients to structure and order flowering plant diversity. Many natural and well-defined genera and families were established during this period. Prominent herbalists and their works are:
Otto Brunfels (1464-1534). German Herbalist. Herbarium Vivae Eicones.Gerome Bock (1469-1554). German. Neu Kreuterbuch.
Leonhard Fuchs(1501-1556). German. De Historia Stirpiu, New Kreuterbuch.
John Gerard (1542-1612). English. The Herball,or, Generall Historie of Plantes.
Rombert Dodoens (1517-1585). Flemish. Cruydeboeck.
Herbalists advanced science of botany but systems adopted by herbalists although commendable in their own way, had very little systematic basis. It was from the sixteenth and seventeenth century onwards that attempts were made to study more and plants and a large number of characters in order to arrive at a satisfactory classification. Some of the 16th and 17th century botanists are:
Andrea Caesalpino (1519-1603), an Italian, tried to base his classification on logic rather than utilitarian concept. He published De Plantis in 1583, which contain description of about 1500 plants. This was the first methodical classification of plants based on definite morphological criteria. Caesalpino recognized the usefulness of fruits and seeds in classification. His views influenced the later botanists like Tournefort, John Ray and Linnaeus.
Casper Bauhin (1560-1624). A Swiss botanist; published Pinax theatri botnici in which he listed 6000 plants. He also provided synonymy i.e. the other names used for a species by earlier workers and binomials for many plants that he named. Bauhin is credited with modern concept of genera and species.
John Ray (1628-1705), a British botanist and philosopher formulated the principle that all parts of the plant should be used for classification- a principle now recognized as the corner stone of a natural system. His system of classification is presented in his Methodus Plantarum (1703), which contain description of 18000 species of plants. He grouped plants by their resemblance to one another and divided the plant kingdom into herbs and trees and further divided herbs into imperpectae (flowerless) and perfactae (flowering plants). Flowering plants and trees were further divided into dicotyledons and monocotyledons.
J.P. de Tournefort (1656-1708). French botanist produced a classification that was purely artificial (based on few features). He is regarded as the “father of genus concept”. In his publication Institutiones Rei Herbarie (1700) he provided descriptions for 698 genera. He differentiated genera on the basis of floral and vegetative characters. Linnaeus later adopted most of the Tournefort’s genera that were distinguished by floral characters.
The systems based on habit and the pre-Linnaean era ends with the system of Tournefort.
The Sexual Or Artificial System
The botanical research on the European flora and subsequent explorations resulted in the collection of more and more plants by the eighteenth century that required a simple and efficient system of naming and classification. This demand produced several purely artificial systems of which Linnaeus’ sexual system is most important
Carolus Linnaeus (1707-1778). It is to Swedish botanist, Carolous Linnaeus, that we owe the modern methods of naming plants. He is considered as “Father of Taxonomy”. Before the time of Linnaeus it was the general custom to name plants with a single name followed by a set of descriptive nouns and adjectives (polynomials). Linnaeus established what has come to known as ‘binomial system’ of nomenclature, which involves naming of plants by two names – one for the genus and one for the species. In addition to establishing the practice of binomial nomenclature, Linnaeus also set up a system of classification that was more comprehensive than any previously devised. This system is usually called as ‘sexual system’ or ‘artificial system’, because Linnaeus based his classification on number of stamens and their relation to one another and to other floral parts. Linnaeus divided plants into 24 classes, of which 23 were of flowering plants and the 24th class includes non-flowering plants i.e. ferns, mosses, fungi and algae. While the artificial approach allowed quick sorting and identification, its application produced unnatural grouping. The important publications of Linnaeus are: Syatema Naturae(1735), Genera Plantarum(1737) and Species Plantarum(1753). Because of the consistent use of binomial nomenclature, the date of publication of his Species Plantarum (Ist May, 1753) is considered as a starting point of the modern botanical nomenclature.
The system of Linnaeus was very simple and convenient and remained in force until the beginning of the 19th century.
Andrea Caesalpino (1519-1603), an Italian, tried to base his classification on logic rather than utilitarian concept. He published De Plantis in 1583, which contain description of about 1500 plants. This was the first methodical classification of plants based on definite morphological criteria. Caesalpino recognized the usefulness of fruits and seeds in classification. His views influenced the later botanists like Tournefort, John Ray and Linnaeus.
Casper Bauhin (1560-1624). A Swiss botanist; published Pinax theatri botnici in which he listed 6000 plants. He also provided synonymy i.e. the other names used for a species by earlier workers and binomials for many plants that he named. Bauhin is credited with modern concept of genera and species.
John Ray (1628-1705), a British botanist and philosopher formulated the principle that all parts of the plant should be used for classification- a principle now recognized as the corner stone of a natural system. His system of classification is presented in his Methodus Plantarum (1703), which contain description of 18000 species of plants. He grouped plants by their resemblance to one another and divided the plant kingdom into herbs and trees and further divided herbs into imperpectae (flowerless) and perfactae (flowering plants). Flowering plants and trees were further divided into dicotyledons and monocotyledons.
J.P. de Tournefort (1656-1708). French botanist produced a classification that was purely artificial (based on few features). He is regarded as the “father of genus concept”. In his publication Institutiones Rei Herbarie (1700) he provided descriptions for 698 genera. He differentiated genera on the basis of floral and vegetative characters. Linnaeus later adopted most of the Tournefort’s genera that were distinguished by floral characters.
The systems based on habit and the pre-Linnaean era ends with the system of Tournefort.
The Sexual Or Artificial System
The botanical research on the European flora and subsequent explorations resulted in the collection of more and more plants by the eighteenth century that required a simple and efficient system of naming and classification. This demand produced several purely artificial systems of which Linnaeus’ sexual system is most important
Carolus Linnaeus (1707-1778). It is to Swedish botanist, Carolous Linnaeus, that we owe the modern methods of naming plants. He is considered as “Father of Taxonomy”. Before the time of Linnaeus it was the general custom to name plants with a single name followed by a set of descriptive nouns and adjectives (polynomials). Linnaeus established what has come to known as ‘binomial system’ of nomenclature, which involves naming of plants by two names – one for the genus and one for the species. In addition to establishing the practice of binomial nomenclature, Linnaeus also set up a system of classification that was more comprehensive than any previously devised. This system is usually called as ‘sexual system’ or ‘artificial system’, because Linnaeus based his classification on number of stamens and their relation to one another and to other floral parts. Linnaeus divided plants into 24 classes, of which 23 were of flowering plants and the 24th class includes non-flowering plants i.e. ferns, mosses, fungi and algae. While the artificial approach allowed quick sorting and identification, its application produced unnatural grouping. The important publications of Linnaeus are: Syatema Naturae(1735), Genera Plantarum(1737) and Species Plantarum(1753). Because of the consistent use of binomial nomenclature, the date of publication of his Species Plantarum (Ist May, 1753) is considered as a starting point of the modern botanical nomenclature.
The system of Linnaeus was very simple and convenient and remained in force until the beginning of the 19th century.
Natural Systems Of Classification (systems based on form relationship)
The wealth of plant material collected by the botanist world over during eighteenth century could not be satisfactorily identified with the help of Linnaeus’ sexual system and a need was realized for a more objective classification. This resulted in the development of still better systems (based on overall resemblance in external morphology), which, unlike artificial systems, involved as many characters as possible.
Michel Adanson (1727-1806), a French botanist, published a two volume work Familles des Plantes (1763). He recognized 58 natural orders according the their natural affinities. He based his classification on using as many characters as possible and giving equal weightage to all the observable characters. This is precursor of modern computer aided Numerical Taxonomy, which is often called Adansonian Taxonomy.
Antonie Laurent de Jussieu (1748-1836), a French botanist published his system in Genera Plantarum (1789) incorporating his uncle’s (Bernard de Jussieu, 1669-1776) work along with his own. He laid emphasis on number of cotyledons, presence or absence of petals and position of the stamens with respect to the ovary.
Augustin Pyrame de Candolle (1778-1841), a Swiss botanist, published his views on classification in his work Theorie Elementaire de la Botanique(1813) and introduced the term Taxonomy do designate the theory of plant classification. He was first to use the characteristics of vascular tissues in the classification of plants and recognized two major groups - Vasculares (Vascular bundle present) and Cellulares (no vascular bundle).
George Bentham (1800-1884) and Sir J.D. Hooker (1817-1911). These two English botanists associated with Royal Botanic Gardens, Kew, presented the most elaborate natural system of classification in their three-volume work Genera Plantarum (1862-83). This was a major landmark in botany, for its system as well as for its quality. All genera of seed plants then known were very carefully and accurately described in Latin observing living specimens or dissected herbarium material. The geographical distribution of each genus was given. They followed de Candolle’s system with some modifications. The Genera Plantarum provided the classification of seed plants, including gymnosperms, describing 200 orders (equivalent to present day families) and 7569 genera. The larger genera were further divided into subgenera and sections. They estimated the seed plant to include 97,205 species. This was the last great work produced on the assumption that angiosperm taxa are fixed entities, unchanging through time and placed on earth by God. British and Indian herbaria are still arranged following the system of Bentham and Hooker.
Bentham and Hooker divided seed plants into three classes (Dicotyledones, Gymnosperms and Monocotyledones), three sub-classes, 21 series, 25 cohorts and 202 orders (initially 200 orders). Orders Vochysiaceae and Cyrillae were incorporated later.
OUTLINE OF SYSTEM OF BENTHAM AND HOOKER, 1862-1883
I. CLASS: DICOTYLEDONES (two cotyledones, exogenous growth)
Sub class 1. POLYPETALAE (petals separate)
Series I. Thalamiflorae (Petals and stamens hypogynous and usually many)
Cohort 1. Ranales (Gynoecium apocarpus)
Orders: 1, Ranunculaceae; 2, Dilleniaceae; 3, Calycanthaceae; 4, Magnoliaceae;
5, Annonaceae; 6, Menispermaceae; 7, Berbaridaceae; 8, Nymphaeaceae
Cohort 2. Parietales (Parietal placentation)
Orders: 9, Sarraceniaceae; 10, Papavaraceae; 11, Cruciferae; 12, Capparideae; 13,
Resedaceae; 14, Cistineae; 15, Violarieae; 16, Canellaceae; 17, Bixineae
Cohort 3. Polygalineae (Calyx and corolla 5, ovary 2 locular)
Orders: 18, Pittosporaceae; 19, Tremendreae; 20, Polygaleae; 20a, Vochysiaceae
The wealth of plant material collected by the botanist world over during eighteenth century could not be satisfactorily identified with the help of Linnaeus’ sexual system and a need was realized for a more objective classification. This resulted in the development of still better systems (based on overall resemblance in external morphology), which, unlike artificial systems, involved as many characters as possible.
Michel Adanson (1727-1806), a French botanist, published a two volume work Familles des Plantes (1763). He recognized 58 natural orders according the their natural affinities. He based his classification on using as many characters as possible and giving equal weightage to all the observable characters. This is precursor of modern computer aided Numerical Taxonomy, which is often called Adansonian Taxonomy.
Antonie Laurent de Jussieu (1748-1836), a French botanist published his system in Genera Plantarum (1789) incorporating his uncle’s (Bernard de Jussieu, 1669-1776) work along with his own. He laid emphasis on number of cotyledons, presence or absence of petals and position of the stamens with respect to the ovary.
Augustin Pyrame de Candolle (1778-1841), a Swiss botanist, published his views on classification in his work Theorie Elementaire de la Botanique(1813) and introduced the term Taxonomy do designate the theory of plant classification. He was first to use the characteristics of vascular tissues in the classification of plants and recognized two major groups - Vasculares (Vascular bundle present) and Cellulares (no vascular bundle).
George Bentham (1800-1884) and Sir J.D. Hooker (1817-1911). These two English botanists associated with Royal Botanic Gardens, Kew, presented the most elaborate natural system of classification in their three-volume work Genera Plantarum (1862-83). This was a major landmark in botany, for its system as well as for its quality. All genera of seed plants then known were very carefully and accurately described in Latin observing living specimens or dissected herbarium material. The geographical distribution of each genus was given. They followed de Candolle’s system with some modifications. The Genera Plantarum provided the classification of seed plants, including gymnosperms, describing 200 orders (equivalent to present day families) and 7569 genera. The larger genera were further divided into subgenera and sections. They estimated the seed plant to include 97,205 species. This was the last great work produced on the assumption that angiosperm taxa are fixed entities, unchanging through time and placed on earth by God. British and Indian herbaria are still arranged following the system of Bentham and Hooker.
Bentham and Hooker divided seed plants into three classes (Dicotyledones, Gymnosperms and Monocotyledones), three sub-classes, 21 series, 25 cohorts and 202 orders (initially 200 orders). Orders Vochysiaceae and Cyrillae were incorporated later.
OUTLINE OF SYSTEM OF BENTHAM AND HOOKER, 1862-1883
I. CLASS: DICOTYLEDONES (two cotyledones, exogenous growth)
Sub class 1. POLYPETALAE (petals separate)
Series I. Thalamiflorae (Petals and stamens hypogynous and usually many)
Cohort 1. Ranales (Gynoecium apocarpus)
Orders: 1, Ranunculaceae; 2, Dilleniaceae; 3, Calycanthaceae; 4, Magnoliaceae;
5, Annonaceae; 6, Menispermaceae; 7, Berbaridaceae; 8, Nymphaeaceae
Cohort 2. Parietales (Parietal placentation)
Orders: 9, Sarraceniaceae; 10, Papavaraceae; 11, Cruciferae; 12, Capparideae; 13,
Resedaceae; 14, Cistineae; 15, Violarieae; 16, Canellaceae; 17, Bixineae
Cohort 3. Polygalineae (Calyx and corolla 5, ovary 2 locular)
Orders: 18, Pittosporaceae; 19, Tremendreae; 20, Polygaleae; 20a, Vochysiaceae
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