In this article we will discuss about the Plant Taxonomy:- 1. History and Development of Plant Taxonomy 2. Classification of Plant Taxonomy 3. Plant Kingdom.
History and Development of Plant Taxonomy:
The early history of development of botanical science is nothing but a history of development of plant taxonomy. The herbalists and agriculturists of ancient times gathered some knowledge about plants which was passed on from generation to generation.
Theophrastus (372-287 BC), the Greek philosopher-scientist, placed this knowledge of plants on a scientific footing. In his “Enquiry into Plants” he dealt with the plants at large and attempted to arrange the plants in several groups. He is, therefore, called the “Father of Botany”.
Pliny compiled a monumental work entitled “Historia Naturalis” where he incorporated all information about plants gathered up to that time and added much to the same collected by himself from his travels far and wide. Disocorides was a contemporary of Pliny and like him travelled a lot and gathered information about medicinal plants.
He compiled his famous book “Materia Medica” where he described about six hundred species of plants mentioning their local name and giving their medicinal properties. Along with descriptions he gave sketches which increased the value of the book very much and gained much popularity among the herbalists and plant-lovers in Europe.
For a long period after this there was no contribution in the study of plants worth mentioning till Albert Magnus in the 13th century wrote his “De Vegetabilis” where the difference in the stem structure of Di-cotyledons and Monocotyledons was shown and the two groups were given the terms Tunicate and Corticate.
Printed books on plants were available towards the close of the 15th century and a few German herbalists carried their enquiries about plants still farther making the study of Botany quite popular.
Foremost among them was Otto Brunfels who published his book “Herbarium vivae Eiconis” in three volumes (1530-1536) which was profusely illustrated with good figures. Jerome Bock (1498-1554), another German herbalist, published his “Nue Kreuterbuch” which contained accurate descriptions of about 600 species of flowering plants.
In this book the author tried to trace the natural relationship of plants while classifying them into 3 major groups, viz., herbs, shrubs, and trees and also noted the original distribution of each species.
Andrea Caesalpino (1519-1603) also classified the plants on the character of their habit, viz., trees, shrubs, and herbs but also took into account the characters of ovary, fruit, and seed. He became famous for his book “De plants” in 16 volumes, the first of which contained his principles of classification.
Leonard Fuchs (1501-1566), Valerius Cordus (1515-1544), Mattias de L’Obel (1538-1616), John Gerard (1545- 1612), and Charles L’Ecluse (1526-1909) were others who also advanced the cause of botanical science by their observations and contributions. Then the Bauhin brothers came to the field.
The elder brother Jean (Johna) Bauhin (1541-1631) wrote a book entitled “Historia plantarum universalis” which was published after his death. Gaspard (Casper) Bauhin, the younger brother (1560-1624), published 3 botanical treatises the third one of which, viz., “Pinax theatri Botanic” became very popular. Both the Bauhins made use of the habit-character of plants in classifying them.
Gaspard Bauhin had formulated the idea of a genus and in many cases gave binary nomenclature to his plants. He also collected all names of plants published in different botanical works till his time and referred them as synonyms along with names he used as correct ones.
John Ray, an English naturalist (1628-1705), set himself seriously to the study of plants and gave much thought in proposing a system of classification of plants. He was the first to recognise 2 major taxa of flowering plants, viz., Dicotyledons and Monocotyledons. He also tried to group the plants into several families which he called “classes”.
He divided the plant kingdom first into 2 groups, viz., Herbae and Arbores. The Herbae were then divided into Imperfectae and Perfectae, the first of which included the Cryptogams and the second group, i.e., the Arbores included most of the flowering plants.
The Perfectae were subdivided into Dicotyledonae and Monocotyledonae and under Dicotyledonae he placed 25 of his classes and 4 under Monocotyledonae. His system of classification came out in his “Historia plantarum” of which several editions were published and he revised and improved his system in the later editions.
Joseph Pitton de Tournefort was a contemporary of John Ray and tried to work out a system of classification of flowering plants. He too divided the plant kingdom first into 2 groups as trees and herbs and used the character of inflorescence and flower for subdividing the latter group.
He was the first to give a clear concept of a genus although Gaspard Bauhin mentioned it in his works. Tournefort’s work proved very helpful in identifying the plants up to the species.
Then came Carolus Linnaeus (1707-1778), a Swedish naturalist (also called Carl von Linne), who gave a new impetus to the study of plants. He was professor of medicine and botany in the Upsala University.
He himself was an arduous collector of plants and made arrangement of collecting plant-specimens from different parts of the world by sending his students to countries far away and through missionary- men and administrators.
The discovery of numerous plants from all over the world led him to think about bringing an order into the existing chaos and set himself in grouping and classifying all the plants known till his time. He proposed a system of classification which was published in his “Systema Naturae” (1735).
In this system he used the character of stamens, i.e., the number and nature of stamens, to distinguish the 20 classes in which he divided the plant kingdom. He also used the number and nature of carpels to distinguish the orders, i.e., subdivisions of his classes.
In addition to presenting an excellent system of classification of plants Linnaeus published many botanical works of monographic and floristic nature and also books embodying his ideas of nomenclature of plants.
The “Species plantarum” the first edition of which came out in 1753 contained an enumeration of all plants known to him till that date, accompanied by brief description of each species with distribution and previous reference. In this work he consistently used binary nomenclature for every species with a generic name followed by a specific epithet.
The modern taxonomists have agreed to consider the year 1753 as the starting point of nomenclature of Phanerogams, Pteridophyta, and Sphagnum. In his “Philosophia Botanica” he laid down some principles which later formed the basis of the International Code of Botanical Nomenclature.
Owing to the efforts of Linnaeus the study of Botanical science entered the modern age and Linnaeus is rightly called the “Father of Modern Botany”.
As in Europe, the study of plants was started by the herbalists in other countries boasting of an ancient civilisation. In India the medical men described many plants of medicinal value and classified them in various ways. Atharva Veda and Susruta Samhita were written before the Christian era.
In his treatise on agriculture Parasara in 6th century classified the plants into many “ganas” or families giving clear picture of the morphology of flowers and fruits. Some of his “ganas” correspond to some families of modern taxonomists.
Sarangadhara in 12th century in his “Upaban Vinoda”, a book devoted to agriculture and horticulture, dealt with different aspects of plant life and classification of plants.
Classification of Plant Taxonomy:
Linnaeus and the botanists before him tried to classify the plant kingdom using a single or a few characters chosen arbitrarily. They only thought about the convenience of following a system of classification solely to identify a particular plant. Such systems are, therefore, called artificial systems of classification.
Later on plant-taxonomists conceived the idea that the plants belonged to some natural groups and they tried to designate and distinguish such groups and tried to classify the plant kingdom accordingly. Such systems are known as natural systems of classification.
Such natural grouping gives the idea that the individuals under one particular group are closely related to one another although they believed in the fixity of species and simultaneous creation of all the groups by God.
After the publication of the theory of Organic Evolution by Charles Darwin and Alfred Wallace the taxonomist began to think about the origin of each of the natural groups from a more primitive group, or from an individual of a more primitive group.
In other words, some of the natural groups are more primitive and some are more recent or advanced and the recent groups have been derived from some comparatively primitive group. A system of classification based on the idea of organic evolution attempting to find out the relation between the different groups, i.e., to trace the phylogeny of the groups, is called the phylogenetic system of classification.
Linnaeus divided the plant kingdom into 24 classes depending on the number and nature of stamens. Each class was subdivided into orders according to the number and 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 and the name given to one order under a class was often given to another order under another class and similarly name of a class was often used to designate an order under another class.
This is an artificial system where very distantly related plants, i.e., plants belonging to widely distant natural groups have been placed under one order of a class. As Linnaeus made use of the morphological nature of stamens and carpels mainly, to classify the plant kingdom his system is also called the sexual system.
Outline of the system is given below:
Linnaeus’s system proved to be of great help in identifying a plant and gained much popularity. Many flora-writers arranged their plants following Linnaeus’s system. William Roxburgh who was the first to write a flora of India adopted the artificial system of Linnaeus in his work, viz., “Flora indica”.
Thunberg, another reputed botanist and a student of Linnaeus also adopted the same system in his books. The disadvantage in using this system is that it gives no indication as to the natural or phylogenetic relationship among different taxa of plants and plants with no affinity at all are sometimes placed together in an artificially created group.
Bernard de Jussieu (1699-1776) who was in charge of the Royal Gardens in France tried to arrange the plants in the gardens following the system of Linnaeus and in doing so modified the system to such an extent that it became altogether a new system of classification.
This, however, was not published and later his nephew Antoine Laurent de Jussieu (1748-1836) published the same in his “Genera plantarum secundum ordines naturales deposita”- with some modifications. This was the first natural system of classification of plants where he established a hundred Natural Orders as taxa above the rank of genera giving distinguishing characters of each.
He divided the plant kingdom into 15 classes and placed the classes under 3 major head; as Acotyledonae, Monocotyledonae and Dicotyledonae. Acotyledonae consists of only one class which comprises the Cryptogams and the Naiades of the monocots, while the Monocotyledonae includes the rest of the monocots in 3 classes.
Dicotyledonae comprises all of the dicotyledonous natural orders and also the Coniferae in the rest of these 11 classes. Jussieu’s system “was slightly modified by Augustin Pyrame de Candolle who was Professor of Botany in Montpellier.
An outline of his system of classification is given below:
Plant Kingdom of Plant Taxonomy:
(Vascular plants; Cotyledons present).
(Vascular bundles in a ring; dicotyledons).
(Calyx and corolla both present)
(Flowers polypetalous and hypogynous; 46 orders starting from Ranunculaceae).
(Flowers poly- or sympetalous and peri- or epigynous; 38 orders from Rosaceae).
(Gamopetalous and hypogynous flowers; 24 orders from Primu- laceae).
(Only calyx present; 19 orders of dicotyledons and Coniferae).
Class 2. Endogenae:
(Vascular bundles scattered).
(Plants bearing flower; 21 orders of monocotyledons).
(Plants without flowers; 5 orders of ferns and fern-allies).
(Plants without vascular bundles; cotyledons absent).
Class 1. Foliaceae:
(Leaves present; male and female gametes distinct; 2 orders comprising the mosses and liverworts).
Class 2. Aphyllae:
(Leaves absent; male and female gametes not distinct; 4 orders including the algae, fungi, etc.). Here he recognised the anatomical characters along with external morphological characters in distinguishing his divisions in the system of classification.
He described 161 natural orders as against 100 of de Jussieu and the different groups or divisions in his system of classification were more natural than those of de Jussieu although he placed the Pteriydophyta in the same class Endogenae with the monocotyledons.
Further he treated the Coniferae as an order in the class Exogenae along with other dicotyledonous orders. De Candolle became famous not for his system of classification but his monumental work entitled “Prodromus systematis naturalis regni vegetabilis”, a book in 17 volumes in which he described all the genera and species of plants discovered up to that time.
The descriptions are very elaborate and are accompanied by references to previous literature and to the area of distribution of each species. He published many other books and formulated a set of rules for naming the plants. It was he who introduced the term taxonomy to designate the study of classifying and naming of plants.
Stephen Endlicher published his “Genera Plantarum” (1836-1840) describing 6,835 genera and arranged them in a system of his own. Here he divided the plant kingdom into 2 regions, viz., Thallophyta and Cormophyta. The Thallophyta included plants with simple structure, without stem or root or vessels and without clearly defined sex-organs, e.g., Algae, Fungi and Lichens.
Cormophyta included plants with stem and roots, having vessels and clearly distinguishable sex-organs. He placed Bryophytes, Pteridophytes and seeds-plants under Cormophyta. He could not recognise the Gymnospermae as a single distinct taxon but placed the Zamiae (Cycads) with the Pteridophyta and the Coniferae with dicotyledons.
The best and most popular of the natural systems of classification is that of George Bentham and Joseph Dalton Hooker, two British Botanists, who classified the Phanerogamia and gave an account of 202 Natural Orders under that group.
This was published in their great monumental work “Genera Plantarum” (1862-1883) where elaborate descriptions of each and every genera and of the Natural Orders were given together with names of all species under each genus, the synonyms, localities and reference to literature.
Keys are also provided for easily identifying the Natural Orders and genera. This book proved to be a very useful reference book which as well as the system of classification given here became very popular in Great Britain and other countries of the world including America.
As noted above only the seed-plants were taken up here and this group was divided into 3 classes, viz., Dicotyledonae, Gymnospermae and Monocotyledonae. The dicotyledons were subdivided into 3 subclasses, viz.—Polypetalae. Gamopetalae and Monochlamydeae.
Each of these subclasses included more than one series. The gymnosperms included only 3 Natural Orders and were not subdivided into subclasses or series. The monocotyledons included 8 series which were not put under any subclass.
The system of classification is given below in a tabular form:
POLYPETALAE: Petals free.
Series i. Thalamiflorae:
Cohort 1 Ranales (8 N.O.)
Cohort 2 Parietales (9 N.O.)
Cohort 3 Polygalinae (4 N.O.)
Cohort 4 Caryophyllinae (4 N.O.)
Cohort 5 Guttiferales (6 N.O.)
Cohort 6 Malvales (3 N.O.).
Series ii. Disciflorae:
Receptacle expanded into a disc; stamens inserted on the disc; ovary superior.
Cohort 7 Geraniales (11 N.O.).
Cohort 8 Olacales (3 N.O.)
Cohort 9 Celastrales (4 N.O.)
Cohort 10 Sapindales (3 N.O.)
Series iii. Calyciflorae:
Flowers perigynous, petals and stamens inserted on a cup-like receptacle, or flowers epigynous.
Cohort 11 Rosales (9 N.O.)
Cohort 12 Myrtales (6 N.O.)
Cohort 13 Passiflorales (7 N.O.)
Cohort 14 Ficoidales (2 N.O.)
Cohort 15 Umbellales (3 N.O.)
Subclass II. GAMOPETALAE: Petals united.
Series i. inferae: Ovary inferior.
Cohort 1 Rubiales (2 N.O.)
Cohort 2 Asterales (4 N.O.)
Cohort 3 Campanulales (3 N.O.)
Series ii. Heteromerae:
Ovary usually superior, carpels more than 2.
Cohort 4 Ericales (6 N.O.)
Cohort 5 Primulales (3 N.O.)
Cohort 6 Ebenales (3 N.O.)
Series iii. Bicarpellatae:
Ovary usually superior, stamens alternating with corolla-lobes, carpels usually 2.
Cohort 7 Gentianales (6 N.O.)
Cohort 8 Polemoniales (5 N.O.)
Cohort 9 Personales (8 N.O.)
Cohort 10 Lamiales (4 N.O.)
Subclass III. MONOCHLAMYDEAE:
Perianth inconspicuous or absent.
Series i. Curvembryeae: Embryo curved, ovule usually one—(7 N.O.)
Series ii. Multiovulatae: Aquaticae: Ovules numerous, aquatics—(1 N.O.)
Series iii. Multiovulatae: Terrestres: Ovules numerous, terrestrials—(3 N.O.)
Series iv. Microembryeae: Embryo very small, ovule usually one—(4 N.O.).
Series v. Daphnales: Ovary monocarpellary, ovule usually one—(5 N.O.)
Series vi. Achlamydosporeae: Ovary unilocular, ovules 1-3, seeds without testa—(3 N.O.).
Series vii. Unisexuales: Flowers unisexual, ovules 1-2—(9 N.O.).
Series viii. Anomalous orders—4.
N.O.s 3, Gnetaceae, Coniferae, Cycadaceae.
Series i. Microspermae: Seeds minute, numerous, exalbuminous—(3 N.O.)
Series ii. Epigynae: Ovary inferior, seeds with copious albumin—(7 N.O.)
Series iii. Coronarieae: Ovary superior, albumin in seeds plenty—(8 N.O.)
Series iv. Calycinae: Perianth sepaloid, ovary superior—(3 N.O.).
Series v. Nudiflorae: Perianth absent or reduced to scales—(5 N.O.)
Series vi. Apocarpae: Carpels free or only one carpel, ovary superior, seeds without albumin—(3 N.O.)
Series vii. Glumaceae: Flowers in spikelets, or in heads, generally subtended by imbricated scale-like bracts, perianth scale-like or glumaceous, seeds with albumin—(5 N.O.)
The system of classification of Bentham and Hooker is the best of all the natural systems. Although it is not a phylogenetic system yet the natural orders (i.e., families) having close relationship have been grouped together in most cases and in phylogenetic classifications of later workers many of such groups have been maintained.
Descriptions of natural orders and genera are very elaborate and accurate, being based on actual study of the specimens by the authors. Therefore for purpose of identification of plants this system is very helpful.
Bentham and Hooker’s system is not a phylogenetic system and is based on the idea of fixity of species. The position of gymnosperms in this system is very unsatisfactory as it has been placed in between the dicots and monocots. Such anomaly is noted also in other cases in placing the natural orders under different series.
The series Curvembryeae with natural orders Nyctaginaceae, Amaranthaceae, Chenopodiaceae, Polygonaceae, Phytolaccaceae, etc. has been placed in Monochlamydeae while Caryophyllaceae which is closely allied to the above-mentioned natural orders has been placed in series Thalamifiorae of Polypetalae.
In monocotyledons inclusion of Irideae and Amaryllideae in the same series with Scitamineae and Bromeliaceae is another example of such anomaly. In the use of terminology of different rank of taxa there is no uniformity.
Thus we find that under the subclasses Polypetalae and Gamopetalae of dicotyledons the natural orders are placed under cohorts which are again placed under series. But in subclass Monochlamydeae and in the monocotyledons the natural orders are placed directly under the series. In gymnosperms the 3 natural orders are not placed under any series or cohort.
A graphical representation of the outline of the system of classification by Bentham and Hooker is given below:
A. W. Eichler, a botanist in Vienna, proposed a new system of classification of the plant kingdom (1875) and this he later elaborated in 1883. Here he gave a more clear idea of the lower groups of plants and also separated the Gymnospermae from the Angiospermae placing them in 2 taxa of equal ranks.
This system is not considered as true phylogenetic but is one that carries the idea of primitiveness and advancement in different groups in the plant kingdom.
An outline of his system is given below:
1. Class Algae
2. Fungi (including Lichens)
1. Class Hepaticae
2. Class Musci
1. Class Equisetineae
2. Class Lycopodineae
3. Class Filicineae
1. Class Monocotyleae
2. Class Dicotyleae
(i) Subclass Choripetalae
(ii) Class Sympetalae
Adolf Engler (Fig. 7), Professor of Botany, University of Berlin, published (1887-1899) in collaboration with Karl Prantl a monumental work entitled “Die naturlichen Pflanzenfamilien” where all the genera of plants were arranged and described systematically.
In doing so they proposed a new system of classification for the whole plant kingdom. This system was based to some extent on that of Eichler but is a true phylogenetic system. In this work they tried to use the terminology for different ranks of taxa in a more scientific way.
The term Natural Order was replaced by the term Family and for a taxon above the rank of families and containing several closely related families they used the term Reihe, equivalent to series or cohorts in Bentham and Hooker’s system.
The Reihe or orders were grouped under Classes, classes under Subdivisions and subdivisions under 13 Divisions in which they divided the Plant Kingdom or Pflanzenreich. The seed-plants, i.e., the Phanerogamia are placed in the 13th division, viz., Embryophyta Siphonogama.
The classification of Phanerogamia according to Engler and Prantl is shown below:
According to Engler the most primitive type of flower is without perianth; the next higher type has one whorl, then there are flowers with two whorls of perianth. Where the perianth is in two whorls, they may be distinguishable into calyx or corolla or not. The gamopetalous condition is an advancement over polypetalous condition.
Indefinite number of stamens and carpels is a primitive condition, while definite number is advanced type. Superior ovary is also a primitive condition from which inferior ovary has come through perigyny. Here it is presumed that the dicots and monocots were derived separately from some extinct group of gymnosperms.
Therefore considering that the Pan-danales among the monocots and Amentiferous dicots nearly approach the ancestral type they are placed at the beginning of the 2 classes of Angiospermae. The Monocotyledonae is placed before Dicotyledonae in this system.
The Monocotyledonae begins with Typhaceae of Pandanales and ends with Orchidaceae of Microspermae. Casuarinaceae the only family of the order Verticillatae is the first family in the Dicotyledonae and the last family is Compositae which is considered to be most highly evolved among the dicotyledonous families.
After the publication of Pflanzenfamilien Engler in collaboration with Gilg brought out a single volume book Syllabus der Pflanzenfamilien containing the system of classification of the plants as proposed in Pflanzenfamilien.
Several editions of this book were published later by Engler and Diels with slight modifications of the system. After Engler’s death Diels published the 11th edition in 1936 and Hans Melchior published the 12th revised edition of the Syllabus (in two volumes) in 1954-64.
Engler’s system was adopted by most botanists and it replaced the Bentham and Hooker’s system in many countries in Europe and America. It has been recognised by the International Botanical Congress. This is a comprehensive system for all groups of plants and is a phylogenetic system.
In the case of Dicotyledons the amalgamation of Polypetalae and Monochlamydeae into one group Archichlamydeae is considered justifiable.
Placing of Orchidaceae at the end of monocots and Compositae at the end of dicots is also considered proper as these 2 families are most highly evolved in their respective classes. The position of Iridaceae, luncaceae and Amaryllidaceae shown to be closer to Liliaceae is also supported by many botanists.
This system has, however, been criticized by many. The origin of monocots is now considered to be from a primitive group of dicots and not separately from the ancestral stock that gave rise to the dicots. It is the Ranales from which the monocots have been derived, and this order is one of the most primitive among the dicotyledons and the position assigned to it in Engler’s system cannot be justified.
The catkin bearing families placed at the beginning of Archichlamydeae are in reality highly advanced as the simplicity of the flowers is the result of reduction and not due to primitiveness. In the case of monocotyledons also the Pandanales consists of the families which are rather recent in the evolutionary line and not at all primitive.
Richard von Wettstein, another German botanist, published a book entitled “Hand-buch der systematischen Botanik” in 1901, a revised edition of which came out in 1935. Here he proposed a system which was similar to that of Engler and Prantl but differing in some cases in tracing the relationship of the orders. He divides dicotyledons into Choripetalae and Sympetalae.
The Choripetalae is again subdivided into Monochlamydeae and Dialypetaleae. There are 29 orders under Choripetalae and 10 orders under Sympetalae. Unlike Engler he considers that the monocots originated from the dicots and from the order Policaripicae.
Further according to him Pandanales is not an order of primitive families but is more advanced over Helobiae and Liliflorae, the two orders from which all other orders of the monocots have been derived.
Charles E. Bessey, Professor of Botany, at the University of Nebreska, U.S.A., also tried to work out the phylogeny of the seed plants, and after several suggestions in that line published in several papers, finally published his system in 1915 under the title “The Phylogenetic Taxonomy of Flowering Plants”.
He divided the group Anthophyta or angiosperms into Alternifoliae (Monocotyledonae) and Oppositifoliae (Dicotyledonae) and each of these 2 classes was subdivided into Strobiloideae and Cotyloideae.
The subclasses under Alternifoliae are further divided into Orders each having one or more Families under it, while the subclasses under Oppositifoliae have Super orders under them and the Super orders have the Orders and Families in descending orders.
Bessey (Fig. 8) considered that the dicotyledonous line is primitive in comparison to the monocotyledonous line and among the dicots, plants with strobiloid type of flowers are very primitive. Therefore he places the Ranales at the beginning of his system of classification as has been done by Bentham and Hooker.
Magnoliaceae of the order Ranales is the most primitive family and Lactucaceae of the Asterales is the most advanced among the Dicots. He splits Compositae into several families and Lactucaceae is one of those new families.
According to Bessey the Anthophyta or the angiosperms originated from the Benettitalean stock and the Alternifoliae, i.e., the Monocotyledonae was derived from the primitive group of Oppositioliae, i.e., the Dicotyledonae.
Bessey prepared a chart to show the relationship of the orders of the Anthophyta and the chart is reproduced below:
In this chart the size of the balloons and other figures is proportional to the number of species in an order. German botanist Hans Hallier proposed another phylogenetic system in his “L’origine et le systeme phyletique des Angiospermes” (1912).
Hallier considered that the angiosperms were derived from some extinct group of Cycad allied to Bennettitlaes. Like Bessey he considered the Monocotyledonae to be more advanced than the Dicotyledonae and the former group was derived from a stock which he called Proberberideae.
He divided the angiosperms into 5 major groups, viz:
(4) Ochnigenes and
There are 29 orders under the Dicotyledonae and 7 orders under the Monocotyledonae.
Like Bessey he considered the Ranales to be the most primitive among the dicots and the plants with amentiferous flowers to be more advanced due to reduction in floral parts. Liliflorae is the first order in his Monocotyledones.
From Liliflorae he derives Helobiae Cyperales, Spadiciflorae, Enantioblastae and Ensatae on one line and Artorrhizae on another line. He splits Amaryllidaceae of earlier botanists to Agavaceae, Alstroemeriaceae and Amaryllidaceae and this treatment has met with the approval of modern workers.
Alfred Barton Rendle of British Museum of Natural History published his book “Classification of Flowering Plants” in 2 volumes in 1904 and 1925. For arranging the families he followed the Engler’s system in general with slight modifications. As in Engler’s system Monocotyledonae was placed before the Dicotyledonae. In the Monocotyledonae the Pandanales is the first order and the Dicotyledonae starts from Salicales.
He breaks up Archichlamydeae into 2 grades, viz., Monochlamydeae and Dialypetalae while Sympetalae remains as grade 3. The Dialypetalae is more advanced over Monochlamydeae and begins with Ranales. Sympetalae originated from Dialypetalae in several lines.
It has been subdivided into 2 groups, the Pentacycliae and the Tetracycliae. Tetracycliae is again divided into Superae and Inferae. In his book the descriptions of families and orders are very elaborate and in many cases the phylogeny of different groups have been nicely discussed.
Even then it is considered that his system is important only from the point of convenience than from phylogenetic standpoint. As in Engler’s system the Monocotyledonae ends in Orchidaceae and the Dicotyledonae terminates in the family Compositae. Like Engler he considered that monocots and dicots originated independently from a common stock.
August A. Pulle of Utrecht Botanical Museum published a system of classification of the Spermatophyta in 1938. This was a slight modification of Engler’s system. According to him spermatophytes are divided into 4 subdivisions, viz., Pteridospermae, Gymnospermae, Chlamydospermae (Gnetales) and Angiospermae.
The last is divided into Monocotyledoneae and Dicotyledoneae. Pulle’s divisions of the extinct and living gymnosperms are considered to be natural groups by most modern workers. He also proposed some changes of position of a few angiospermic orders in the Engler’s system to show their affinities.
John Hutchinson, a British Botanist working in the Royal Botanic Garden, Kew, London, published a phylogenetic system for classifying the families of angiosperms in his book “The Families of Flowering Plants”. The first volume containing the dicotyledons appeared in 1926 and the second volume in 1934 and a revised edition of the 1st volume was published in 1960.
He divided his Phyla-Angiospermae into 2 subphylas, viz., Dicotyledones and Monocotyledones. The dicotyledons originated according to him from an ancestral stock called Proangiospermae allied to Bennettitales. The primitive dicotyledons developed in 2 separate lines one bing predominantly woody and the other herbaceous.
The primitive dicots with hermaphrodite, hypogynous flowers with numerous free and spirally arranged parts are placed in Archichlamydeae from which the Metachlamydeae is derived.
In the revised system he abolished the groups Archichlamideae and Metachlamideae, and placed the woody families under division Lignosae and the herbaceous families under division Herbaceae, the 2 groups originating in 2 separate lines from the Proangiospermae.
The Monocotyledones originated according to him from the Ranales, and were subdivided by him into 3 divisions, viz., Calyciferae, Corolliferae and Glumiflorae. Here also those families are considered as primitive which have usually hermaphrodite, hypogynous flowers with numerous, free and spirally arranged parts.
Such families among the monocots are almost all aquatic and therefore he concludes that the Monocotyledones were derived from primitive Dicotyledones through aquatic medium. Butomales and Alismatales are considered most primitive among the monocots from which other families of Calyciferae have been derived.
Corolliferae has been derived from Butomales and Commelinales of Calyciferae. Liliales forms the basal stock of other orders of Corolliferae and also of Glumiflorae the 3rd divison of the Monocotyledones. He splits Pandanales of Engler to Pandanales and Typhales and considers the families under them to be much more recent and not at all primitive.
He splits Liliaceae of the older botanists to Liliaceae, Tecophilaeaceae, Trilliaceae, Smilacaceae and Ruscaceae and transfers Draceneae to Agavaceae, Luzuriageae to Philesiaceae and Allieae to Amaryllidaceae. This treatment of the older Liliaceae meets with the approval of most modern botanists.
The system of classification of the monocots by Hutchinson (Fig. 9) appears to be more satisfactory than any other systems proposed by earlier workers on this line. Reshuffling of the orders and rearrangement of the families have gained support from anatomy and cytology.
The origin of monocots from the primitive dicots is now considered a fact agreed upon by all modern taxonomists. In the case of dicots, however, dividing the group into 2 separate divisions from the beginning into Lignosae and Herbaceae seems to be arbitrary and illogical.
And as a result of this many natural families had to be vivisected unnecessarily and the phylogeny was mixed up rather than simplified. Placing of Magnoliales and Ranales at the beginning of dicots and consideration of the Amentiferae as a more advanced group are the points that have been supported by other workers.
Professor Oswald Tippo of Illinois University, U.S.A., proposed a system of classification in 1942 for the major taxa of the whole of the plant kingdom. Here he took into consideration the anatomical, paleobotanical and morphological characters and followed Gilbert Smith and Eames to a great extent.
He divided the Plant kingdom into 2 Subkingdoms, viz., Thailophyta and Embryophyta, each having several Phyllas. In the Embryophyta there are 2 Phyllas, viz., Bryophyta and Tracheophyta. Phyllum Tracheophyta contains 4 subphyllas, viz., Psilopsida, Lycopsida, Sphenopsida and Pteropsida.
Under Pteropsida there are 3 classes, viz:—Filicinae, Gymnospermae and Angiospermae. Under class Angiospeimae there are 2 subclasses, viz., Dicotyledonae and Monocotyledonae. The arrangement of the orders and families of these 2 sub classes have not been shown here.
Alfred Gunderson published a book in 1950, entitled “Families of Dicotyledons”. In this book the class Dicotyledonae has been divided into 42 orders to include 242 families of which 240 are distributed under the 42 orders and 2 are placed at the end as Incertae Sedis (put apart).
Magnoliales is the first order among the dicots and is followed by Ranales. The last order is Asterales containing 3 families, viz., Calyceraceae, Compositae and Chicoriaceae. He has given cytological data for the families as far as available.
In 1954 L. A. Kuprianova, a Russian Botanist, published a scheme to show the phytogeny of the class Monocotyledonae based on 1’alynological data. She concludes that the monocots have been derived from the Proangiospermae or Protoanthophyta along different lines directly as well as through the Polycarpicae of the dicots.
The Monocotyledonae therefore is polyphyletic in origin. The families Liliaceae and Palmae are derived directly but separately from the Proangiospermae, Alismataceae and Juncaginaceae from Ranales and Araceae probably from Piperales of the Dicotyledonae.
Liliaceae gave rise to Thurniaceae, Juncaceae and Cyperaceae in one line and from Amaryllidaceae to Orchidaceae in another line. Palmae gave rise to Cyclanthaceae, etc. to Graminae. Araceae gave rise to Lemnaceae, and the Helobiae group of families were derived from Alismataceae and Juncaginaceae.
The problem of classifying the Angiospermae engaged the attention of many recent workers and the systems proposed by A. Takhtajan and also by A. Cronquist have been very popular as these are considered to be very near perfection and show the natural affinities much more clearly between different taxa of flowering plants.
Armen Takhtajan is a reputed Palaeobotanist working in the Komarov Botanical Institute of Leningrad. He has also made great contributions in the field of angiosperm taxonomy and proposed a system of classification of angiosperms in 1942 based on the structural types of gynoecium and placentation.
Later on the proposed another system in 1959 where he splits Ranales into Magnoliales, Illiciales, Tochodendrales, Ranales and Dilleniales. He also splits Nymphaeales into Nymphaeales and Nelumbonales. According to him Monocotyledonae was derived from Dicotyledonae along Nymphaeales through aquatic medium.
Magnoliales is the most primitive order among the Dicotyledonae from which the other orders of this class originated. He further modified this system and published the same in his book entitled “Flowering plants, Origin and Dispersal” in 1969.
Here he adopted new terminology for the higher taxa also according to the rules of nomenclature of plants. He therefore, calls the Angiospermae as Magnoliophyta, the Dicotyledonae as Magnoliatae and the Monocotyledonae as Liliatae.
An outline of his system may be graphically represented as shown below:
Arthur Cronquist of New York Botanic Garden drew out a scheme to show the relation of the orders of Dicotyledonae in 1957. Later on in 1965 he published a paper discussing the problem of classification of Flowering Plants where he recognised 5 complexes among the Dicotyledonae.
Of these 5 complexes Ranalian complex is the most primitive and from this complex the other complexes of Dicotyledonae as well as the class Monocotyledonae have been derived. Finally he published his book, “Evolution and Classification of Flowering Plants” in 1968 where he classified the Dicots or the Magnoliatae into 6 subclasses, viz., Magnoliidae, Dilleniidae, Caryophyllidae, Hamamelidae, Rosidae and Asteridae.
Magnoliidae is the most primitive subclass from which Dilleniidae, Caryophyllidae, Hamamelidae and Rosidae have been derived while Asteridae originated from Rosidae. The relationship of these six subclasses has been shown graphically by him with the help of balloon like figures, the sizes of the balloons giving an idea of the number of orders and families in each subclass.
This is reproduced below:
He derives the names of the subclasses from an order included under it and what forms the basal stock for the other orders in that subclass except in the Asteridae where Asterales is the highest order containing the more recent families among the dicots (or Magnoliatae). The most primitive order in that subclass is the Gentianales which, however, does not form the basal stock for other orders in Asteridae.
As noted before Cronquist considers that the monocots or the class Liliatae originated from some primitive dicot order included in the Ranalean complex, i.e., in the subclass Magnoliidae. Like Takhtajan he classifies the Liliatae into 4 subclasses, viz., Alismatidae, Arecidae, Liliidae and Commelinidae and represents them graphically as shown below:
In the revised edition of his book Cronquist names the 2 classes of Angiosperms as Magnoliopsida and Liliopsida. Here he divides the Liliopsida into 5 subclasses as graphically represented below:
C. Mez, a German botanist, advanced a theory that relationship between the major groups of plants could be determined by serochemical tests or serum diagnosis. Working with H. Ziegenspeck he prepared a phylogenetic tree in 1926 to show the evolution of plant life from the Thallophyta to Angiosperms.
Here they showed that among the dicots Trochodendraceae, magnoliaceae, Anonaceae, Aristolochiaceae, Myrtaceae, etc. are the most primitive families and the nomocots branched off from a stock which give rise to these primitive dicots.
They consider that Compositae is at the highest position in the main line of evolution. Alismataceae, Juncaginaceae, Butomaceae, etc: occupy the basal position of the monocotyledonous branch while the grass family, Eriocaulaceae, Restionaceae, Orchidaceae and Zingiberaceae terminate the branches at the top.
This is an attempt to solve the problem of tracing the phylogeny of the plant groups from a different angle. This, however, has not gained much popularity.
Primitive and Advanced Characters in Angiosperms:
It is presumed that the immediate ancestor of the angiosperms had a strobilus-like flower. In such a flower the thalamus was long and on this there were indefinite number of stamens (microsporophyll’s) and pistils (megasporophylls) spirally arranged. In habit the plants were trees with secondary growth and broad net-veined leaves.
In course of evolution modifications appeared in all parts of the plant and in tracing the phylogeny of different groups of plants it is necessary to realise and distinguish the primitive and advanced characters manifested in different groups.
In angiosperms the primitive and advanced characters are noted below: