Consortium for Educational Communicationeacharya.inflibnet.ac.in/data-server/eacharya-documents/57189ee98... · Consortium for Educational Communication Module on Salient Features

Consortium for Educational Communication

Module on Salient Features of Classification system by Bentham and Hooker

ByDr. Hilal Ahmad Lone

Assistant Professor,Department of BotanyGovernment College

Baramulla,Contact No. 9797716299E. mail [email protected]


TextThe science which deals with the classification of organisms

is called taxonomy, a term coined by the famous French botanist, A. P. de Candolle (1813), and which stems from two Greek words-‘taxis’ meaning arrangement and ‘nomos’ meaning study. The term taxonomy is sometimes taken as a synonym of systematics. According to the palaeontologist George Gaylord Simpson (1961; 67), “Systematics is the scientific study of the kinds and diversity of organisms and of any and all relationships among them”.

There are four components of taxonomy-description, identification, classification and nomenclature. The description of a taxon is a statement of its attributes and characteristics, and the description is obtained from the thorough and careful examination, observation and study of the plants. In taxonomic procedure, description and identification precede classification, which precedes nomenclature. That is, description-cum-identification is the basic process in taxonomy which involves determining whether an unknown plant belongs to a known, named group of plants; and there are three ways to achieve it. These include (i) the help from a professional botanist or a well-trained naturatlist who knows the plants of a region, (ii) with the help of Floras, or other literature, and (iii) the herbaria. On the other hand, nomenclature is the assignment and application of scientific names to the already identified and classified plants.

Classification is the placement of an entity in a logically organized scheme of relationships. It is, in fact, the formation of ordered groups and subgroups of a particular lump of objects, such as living beings. The first to write down a classification of plants in a permanent and logical form was the ‘father of botany’ Theophratus (c. 320-285 B. C.). Contributions of the Swede, Carl Linne, usually Latinized as Carolus Linnaeus (1707-1778) to the


science of taxonomy are so vast as to entitle him as ‘ father of taxonomy’. He popularized and customerised the binomial system of nomenclature, that has already been proposed and designed by G. Bauhin (1560-1624) in 1590, but not followed with consistency.

The history of taxonomy has no horizons as it had its roots in the origin of human species and civilization with glorious past, present, and more so a future is anticipated. Classification has been actually a need-based practice, and hence, the classificatory systems are transient in nature. They continued to be modified and improved as a result of new findings. Davis and Heywood (1963) in their book entitled, “Principles of Angiosperm Taxonomy” have quoted Tindall Hopewood saying as “ the urge to classify things is a fundamental human instinct; like the predisposition to sin, it accompanies us in to the world at birth and says with us to the end”. All modern systems have a past and are essentially modifications of the earlier ones (Sivarajan, 1991) and historically plant classifications (like those of animals) belong to three categories: (A) Artificial classification: The earliest and ancient system of classification had been of this category and here the plants, or living creatures, were grouped on their few superficial and easily observable features. These systems are described as artificial because many plants in a category are not closely related to each other by descent from a common ancestor; and these artificial systems typically have the goal of easy plant identification by means of one or a few characters. The artificial classifications are very low in predictivity and are often designed to suit a special purpose of its users and are, therefore, also called special purpose classifications. Classification of plants in to trees, shrubs, sub-shrubs and herbs by Theophrastus and, about twenty centuries


after him, the ‘Sexual system’ of plants by Linnaeus on the basis of the number of stamens and carpels are artificial.(B) Natural classification: According to Lawrence (1951) ”the pre-Darwinian naturalists, accepting the dogma of Special Creation, believed that the natural system of classification and a Divine plan were the same. To them, a natural system was one in accord with nature, and which represented life as it occurred in nature”.

John Ray (1628-1705) and Michel Adanson (1727-1806) were the earliest advocates of natural classification. Following them were Antoine Laurent de Jussieu (1686-1758) , Augustine Pyrame de Candolle (1778-1841) and his son A. de Candolle (----).

The natural classificatory systems are the ones based on large number of characters of the organisms. Because these classification systems attempt to yield homogenous grouping of plants closely related to each other by descent from a common ancestor, hence, these groups are termed as natural groups and the classification as natural. The natural classifications are very predictive and fulfill the needs of the greatest possible number of their users and are hence called general purpose classifications.

Since all the details of plant phylogeny are yet unknown, the construction of a definitive natural system, correct in every detail, is still awaited and, therefore, many of the so-called natural systems are artificial to some extent. The classification of seed plants by Bentham and Hooker (1862-1883) is one amongst such systems.(C) Phylogenetic classification: These post-Darwinian systems are the most advanced and recent by origin. They are based on the evolutionary/phylogenetic history and genetic


affinities of the organisms and, therefore, most desirable. At the same time they are very troublesome to develop because (i) the same organism has an amalgam of primitive and advanced characters, (ii) evolution has occurred in several directions, (iii) the fossil record of any species is imcomplete, which is helpful in constructing the phylogenetic maps, and (iv) certain groups are rich in fossils than others. Plant classification by Hutchinson (1948) and Armen Takhtajan (1959) are examples of phylogenetic ones.A classification system may serve in a number of ways:

i. All classifications aim at achieving economy of memory by making the study of organisms easy and time-saving,

ii. Serve to store information about organisms,iii. Helps to understand affinities amongst organisms, andiv. May be useful as predictors. Predictivity is one of the

most obvious criteria that can be used to assess how good a classification is. A more natural classification is more predictive and vice-versa.

Bentham and Hooker system of classification of seed plants-salient features

The last major and the most accepted natural system of classification of seed plants was that of Bentham and Hooker. It is a natural system of classification and is based on important characters of the plants. Even today this system is being followed in India, United Kingdom and several other Commonwealth countries. It is also used in a number of herbaria and botanical gardens all over the world. It is a well known and widely accepted classification of seeded plants. It was proposed by two British botanists George Bentham (1800-1884) and Sir Joseph Dalton Hooker (1817-1911). They were associated with Royal Botanical


Garden at Kew and adopted a very comprehensive system of classification which is purely natural and most convenient and extremely suitable system for practical utility in identification of plants providing them, their respective taxon. This was the greatest taxonomic work ever produced in the United Kingdom and has ever since been an inspiration to generations of Kew botanists. Their system of classification was published in ‘Genera Plantarum’ in three volumes and they had described 97,205 species of seeded plants in 202 orders (now referred to as families). This three-volume monumental work which required quarter of a century, comprised description of all genera of seed plants known to science at that time and they were classified according to the system proposed by them. This system was published well before there were internationally accepted rules for botanical nomenclature. It indicates a family by “order”; an order is indicated by “cohorts” (in the first two volumes) or “series” (in the third volume); in the first two volumes “series” refers to a rank above that of order.

The system of classification by Bentham and Hooker is based on groups of plant characters which are correlated with each other. For example, if a specimen consistently shows syngenesious stamens, inferior, bicarpellary, unilocular ovary, with basal placentation, then it can confidently be assigned to the family Compositae. Basically, it is on the same basis as that of the de Candolle but with some modifications such as greater emphasis on the free and fused condition of petals.Main features of classification:

1. This system includes the names and descriptions of all genera, of seed plants known so far and classified accordingly.

2. This system divided seed plants into 97,205 species under


202 order or families.3. They divide seed plants into three classes in sequence-

Discotyledon, Gymnosperm and Monocotyledon.4. Dicots divided into 3-divisions and 14 series on the basis of

the natural and visual characteristic which provides key for identification.

5. Dicots started with family Ranunculaceae having free sepals and petals and indefinite number of stamens and carpels where as it ends with Labiatae having fused sepals and petals with definite number of carpels and stamens.

6. Among monocots out of seven series with epigynous flower i.e. Orchidaceous and Scitamineae were kept first and second respectively followed by with petaloid hypogynous flowers and finally ended with Graminae and Cyperaceous.

Outline of classification system proposed by Bentham and Hooker

An outline of this classification system is presented here, but we name Cohorts and Ordines (Ordos) of Bentham and Hooker, respectively as Orders and Families.

The seeded plants are divided into three classes-Dicotyledonae, Gymnospermae and Monocotyledonae. Class-I Dicotyledonous

Seeds of dicotyledonous plants contain two cotyledons. Stem with open bundles. Leaves show reticulate venation. Flowers are tetramerous or pentamerous having four or five members in various floral whorls respectively. It includes three sub-classes-Polypetalae, Gamopetalae and Monochlamydeae.Sub-class 1. Polypetalae

Plants having flowers with free petals come under polypetalae. Theflowers are with distinct calyx and corolla. It is further divided


into three series-Thalamiflorae, Disciflorae and Calyciflorae.Series-I Thalamiflorae

It includes plants having flowers with dome or conical thalamus. Ovary is superior. Petals and stamens hypogynous, Disc present. Thalamiflorae includes 6 orders and 34 families. The six orders or cohorts and the respective families are Ranales (Ranunculaceae, Dilleniaceae, Calycanthaceae, Magnoliaceae, Anonaceae, Menispermaceae, Berberideae, and Nymphaceae), Paraietales (Sarraceniaceae, Papaveraceae, Cruciferae, Capparideae, Resedaceae, Cistineae, Violarieae, Canellaceae and Bixineae), Polygalineae (Pittosporeae, Tremandreae, Polygalae and Vochysiaceaaaaae), Caryophyllineae (Frankeniaceae, Caryophylleae, Portulaceae and Tamariscineae), Guttiferales (Elatineae, Hypericineae, Guttiferae, Ternstroemiaceae, Dipterocarpeae and Chlenaceae) and Malvales (Malvaceae, Sterculiaceae and Tiliaceae).Series- II Disciflorae

It includes flowers having prominent disc- shaped thalamus below the ovary. Ovary is superior. Disciflorae is divided into 4 orders and 23 families. The four orders or cohorts and the respective families of Disciflorae are Geraniales (Lineae, Humiriaceae, Malpighiaceae, Zygophylleae, Geraniaceae, Rutaceae, Simarubeae, Ochnaceae, Burseraceae, Meliaceae and Chailletiaceae), Olacales (Olacineae, Ilicineae and Cyrillaceae), Celastrales (Celastrineae, Stackhousieae, Rhamneae and Mpelideae) and Sapindales (Sapindaceae, Sabiaceae, Anacardiaceae, Coriariae and Moringeae).Series-III Calyciflorae

It includes plants having flowers with cup- shaped thalamus. Ovary is superior or inferior sometimes half inferior. Calyciflorae includes 5 orders and 27 families. The five orders or cohorts of Calyciflorae and their respective


families are Rosales (Connaraceae, Leguminosae, Rosaceae, Saxifragaceae,Crassulaceae, Droseraceae, Hamamelideae, Bruniaceae and Halorageae), Myrtales (Rhizophoreae, Combretaceae, Myrtaceae, Melastomaceae, Lythrarieae and Onagrarieae), Passiflorales (Samydaceae, Loaseae, Turneraceae, Passifloreae, Cucurbitaceae, Begoniaceae and Datisceae), Ficoidales (Cacteae and Ficioideae) and Umbellales (Umbelliferae, Araliaceae and Cornaceae). Sub-class 2. Gamopetalae

Plants having flowers with petals, which are either partially or completely fused to one another are placed under Gamopetalae. The sepals and petals are distinct. Gamopetalae is further divided into three series-Inferae, Heteromerae and Bicarpellatae.Series-I Inferae

The flowers are epigynous and ovary is inferior. Inferae includes 3 orders and 9 families. The three cohorts of Inferae are Rubiales (Caprifoliaceae and Rubiaceae), Asterales (Valerianeae, Dipsaceae, Calcereae and Compositae) and Campanales (Stylidieae, Goodenovieae and Campanulaceae). Series-II Heteromerae

The flowers are hypogynous and ovary is superior with more than two carpels. Heteromerae includes 3 orders and 12 families. The three cohorts of Heteromearae are Ericales (Vacciniaceae, Ericaceae, Monotropeae, Epacrideae, Diapensiaceae and Lennoaceae), Primulales (Plumbagineae,Primulaceae and Myrsineae) and Ebenales (Sapotaceae, Ebenaceae and Styraceae). Series-III Bicarpellatae

The flowers are hypogynous and ovary is superior with two carpels only. Bicarpellatae includes 4 orders and 24 families. The four orders or cohorts of Bicarpellatae are Gentianales (Oleaceae, Salvadoraceae, Apocynaceae, Asclepiadeae,


Loganiaceae and Gentianeae), Polemoniales (Polemoniaceae, Hydrophyllaceae, Boragineae, Convolvulaceae and Solanaceae), Personales (Scrophularineae, Orobranchaceae, Lentibularieae, Columelliaceae, Gesneraceae, Bignoniaceae, Pedalineae and Acanthaceae) and Lamiales (Myoporineae,Selagineae, Verbenaceae, Labiatae and Plantagineae). Sub-class 3. Monochlamydeae

Plants having flowers with single whorl of perianth are placed under Monochlamydeae. Flowers are incomplete. The sepals and petals are not distinguished and they are called perianth. Tepals are present in two whorls. Sometimes both the wholrs are absent. Monochlamydeae includes 8 series and 36 families.

(i) Curembryeae (embryo curved round the endosperm, ovule usually one). Curembryeae is represented by families like Nyctagineae, Illecebraceae, Amarantaceae, Chenopodiaceae, Phytolaccaceae, Batideae and Polygonaceae.

(ii) Multiovulate aquaticae (aquatics with numerous ovules). It is represented by a single family of Podostemonaceae.

(iii) Multiovulate terrestris (terrestrial plants with numerous ovules). The various families of the series are Nepenthaceae, Cytinaceae and Aristolochiaceae.

(iv) Microembryeae (embryo very small in copious endosperm). Piperaceae, Chlorantaceae, Myristiceae and Monimiaceae are its representative families.

(v) Daphnales (ovary usually with one carpel and single ovule). Daphnales is represented by families like Laurineae, Proteaceae, Thymelaceae, Penaeaceae and Elaeagnaceae.

(vi) Achlamydosporae (ovary usually inferior, unilocular and one to three ovuled). It is represented by families like Loranthacceae, Santalaceae and Balanophoreae.


(vii) Unisexualis (flowers unisexual). The various families of Unisexualis are Euphorbiaceae, Balanopeae, Urticaceae, Platanaceae, Leitnerieae, Juglandeae, Myricaceae, Casuarineae and Cupuliferae.

(viii) Ordines anomali (the families of uncertain relationship were placed in this series). The various families of Ordines anomaly are Salicineae, Lacistemaceae, Empetraceae and Cerastophlleae.

Class II GymnospermaeThe members of this class have naked ovules or seeds.

Ovary is absent and gymnospermae includes three families – Gnetaceae, Coniferae and Cycadaceae.Class-III Monocotyledons

Usually herbs, some are shrubs, seed with one cotyledon in embryo.It includes seven series, viz (i) Microspermae (ovary inferior, seeds very small). The

various families of Microspermae are Hydrocharideae, Burmanniaceae and Orchideae.

(ii) Epigynae (ovary usually inferior, seeds large). The various families of Epigynae are Scitamineae, Bromeliaceae, Haemodoraceae, Iirideae, Amaryllideae,Taccaceae and Dioscoreaceae.

(iii) Coronarieae (perianth petaloid, ovary superior). The various families of Coronarieae are Roxburghiaceae, Liliaceae, Pontederiaceae, Philydraceae, Xyrideae, Mayaceae,. Commelinaceae and Rapateaceae.

(iv) Calycinae (perianth sepaloid, ovary superior). Calycinae include families like Flagellarieae, Juncaceae and Palmae.

(v) Nudiflorae (perianth mostly lacking, ovary superior). Nudiflorae include the families like Pandaneae, Cyclanthaceae,Typhaceae, Aroideae and Lemnaceae.


(vi) Apocarpae (carpels free). The Apocarpae is represented by families like Triurideae, Alismaceae and Naiadaceae.

(vii) Glumaceae (perianth small, scale-like or chaffy). The Glumaceae is represented by families like Eriocauleae, Centrolepideae, Restiaceae, Cyperaceae and Gramineae.

From this classification, it is understood that if we proceed from the beginning considering the morphological characters of a species we can easily identify it to place it in its specific taxon.Merits and demerits of Bentham and Hooker’s system of classification Not a single classification can claim to be perfect, satisfactory and free of vice. This fact forms the basis for the wide array of classificatory systems from time to time. The above system is no exception and a number of its merits and demerits have come to limelight.Merits

1. Bentham and Hooker’s classification is the most natural system, based on actual examination of specimens.

2. The description of plants is quite accurate and reliable.3. As it is easy to follow, it is used as a key for the identification

of plants in Kew herbarium and several other herbaria of the world.

4. Although this system is natural, most of the aspects of this system show affinity to modern concepts of evolution. For example, the order Ranales, which is the first order in the arrangement of plants, has been given a primitive position in this system. Recent taxonomic findings also indicate that the members of Ranales are the most primitive living angiosperms.

5. Each family had a synopsis at the beginning which is very useful in identification.

6. The gamopetalae placed after polypetalae is justified since


union of petals is considered to be an advanced feature.7. Treating Cucurbitaceae and Umballiferae at the end of

Polypetalae as connecting links between polypetalous and gamopetalous families.

8. Creation of Monochlamydeae at the end of Dicots.9. Disputed families included in Ordines anomaly.10. Placing of unisexual monocot families after bisexual

families e.g. Palmae and Araceae after Liliaceae.11. The series Glumaceae with extremely reduced flowers

and inflorescences , placed at the end of the flowering plants.12. The placement of monocotyledonae after the

dicotyledonae also appears to be in accordance with the evolutionary trends.

13. The system was never conceived by its authors on the basis of phylogeny. The theory of organic evolution was announced independently by Darwin and Wallace in 1869. So, any criticism of the system on the basis of phylogeny is not too justified.

Demerits 1. The system does not give any idea as to the evolutionary

history of any genus, family or order. 2. In this system grouping of plants is mainly based on single

and artificial characters, with the result, that closely allied families are widely apart.

3. The group Monochlamydeae is entirely artificial.4. The placement of Gymnospermae in between dicotyledonae

and monocotyledonae is an error.5. Several important floral characters have been neglected in

this system.6. Advanced family Orchidaceae has been considered as

primitive among monocotyledons and it is placed in the beginning of the system.


7. In this system, some closely related families have been separated and placed under different groups. For example, all the families of series Curvembryeae of Monochlamydeae are related to Caryophyllaceae of series Thalamiflorae of Polypetalae, but they are separated.

8. Unrelated families have been grouped nearer. For example, Podostemaceae of series Multiovulatae aquaticae of Monochlamydeae deserves a place in Rosales of the series Calyciflorae of Polypetalae. Similarly, Laurineae of series Daphnales of Monochlamydeae deserves a place in Ranales of the series Thalamiflorae of Polypetalae. Thus, two unrelated families Podostemaceae and Laurineae are grouped nearer.

9. The position of series Apicarpae is unsatisfactory due to its free and superior carpels.

However, in spite of all its disadvantages, the Bentham and Hooker system is still very popular in many countries, because identification of plants in the field is comparatively easy. It is followed in the Kew Herbarium for the arrangement of plant specimens, as also in many other herbaria, particularly those of the Commonwealth countries.


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