ARTIFICIAL SYSTEM OF CLASSIFICATION

Artificial System of Plant Classification | Taxonomy | Botany

List of four eminent botanists who contributed to artificial system of plant classification:- 1. Theophrastus (370-287 BC) 2. John Ray (1627-1705) 3. Carolus Linnaeus (1707-1778) 4. George Bentham (1800-1884) and Joseph Dalton Hooker’s (1817-1911) System.

Botanist # 1. Theophrastus (370-287 BC):

He was a Greek naturalist and pupil of Plato and Aristotle. Based on the habit, he classified the plants into four (4) groups: Herbs, Undershrub, Shrubs and Trees. He described and named about 480 plants and published his work in Historia Plantarum, known as the oldest botanical work in existence.

Some of his important contributions are men­tioned:

1. Fundamental differences between Dicoty­ledons and Monocotyledons;

2. Difference between centripetal (racemose) and centrifugal (cymose) type of inflores­cences;

3. Difference between polypetalous and gamopetalous corolla;

4. Difference between superior and inferior ovary, etc.

Some of the names given by him received general recognition and some are also used as generic names in modern classification, e.g., Aspharagos (Asparagus), Daukan (Daucas) etc.

For the above immense contributions, Theophrastus is called the “Father of Botany”.

Andrea Cesalpino (1519-1603) classified the plants first on the basis of habit and secondarily on the characteristics of fruits and seeds. He is usually regarded as the “First Plant Taxonomist”.

Later. Gaspard (Casper or Kaspar) Bauhin (1560-1624) in his work frequently referred the plants with a binary nomenclature and made distinction between genus and species.

Botanist # 2. John Ray (1627-1705):

He was a British botanist. Initially, he proposed his classification in Methodus Plantarum Nova (1682). Later on, he represented his classification in Historia Plantarum (1686-1704) in three volumes. Like other old systems, he classified the plants into herbs and trees and further into Dicotyledons and Monocotyledons. His system was much advanced than the earlier classifications and approached the natural system.

The outline of his system is:

A. Herbae (herbs):

i. Imperfectae (Non-flowering plants i.e., cryptogams).

ii. Perfectae (Flowering plants)

a. Dicotyledons.

b. Monocotyledons.

B. Arborae (trees and shrubs):

a. Dicotyledons.

b. Monocotyledons.

Botanist # 3. Carolus Linnaeus (1707-1778):

He was a Swedish naturalist. For his outstanding contribu­tion he is called the “Father of Modern Botany”.

He published his work in different times since 1730 to final form in 1753.

The publications are:

1. 1730 — Hortus Uplandicus (contains the plants of Uppsala Botanic Garden at that time).

2. 1735 — Systema Naturae.

3. 1737 — Hortus Cliffortianus (contains the plants in the Garden of George Clifford at Hartecamp).

4. 1737 — Genera Plantarum.

5. 1738 — Classes Plantarum.

6. 1751 — philosophia Botanica (contains the revised revision of his earlier publications Systema Naturae and Classes Plantarum.

7. 1753 — Species Plantarum (contains some 7,300 species described and arranged according to his system of classification). In this book, he constantly used the binomial system in plant names. The Binomial system consists of two names of a specimen, where the first one is the generic epithet and the second is the specific epithet. This binomial system was used subsequently, even by the modern botanists till date.

The classification of Linnaeus is an artificial one. The significance of flower and fruit struc­tures was first recognised by him. He empha­sised the basic numerical characteristics of sexual parts i.e., stamens and carpels. Thus the Linnaeus system is also known as sexual system.

Based on the number, size, length and union of stamens, he classified the plant kingdom into 24 classes, such as Monandria (flower with one stamen), Diandria (flower with two stamens), etc. The classes were further divided into orders, based on the number of styles in each flower such as Monogynia (flower with one style), Digynia (flower with two styles) etc.

The outline of Linnaeus System of classification with twenty four (24) classes is given:

Classes:

1. Monandria (flowers with 1 stamen).

2. Diandria (flowers with 2 stamens).

3. Triandria (flowers with 3 stamens).

4. Tetrandria (flowers with 4 stamens).

5. Pentrandria (flowers with 5 stamens).

6. Hexandria (flowers with 6 stamens).

7. Heptandria (flowers with 7 stamens).

8. Octandria (flowers with 8 stamens).

9. Enneandria (flowers with 9 stamens).

10. Decandria (flowers with 10 stamens).

11. Dodecandria (flowers with 12 stamens).

12. Icosandria (flowers with more than 20 stamens are attached to the calyx).

13. Polyandria (flowers with more than 20 stamens are attached to the receptacle).

14. Didynamia (stamens didynamous).

15. Tetradynamia (stamens tetradynamous).

16. Monadelphia (stamens monadelphous).

17. Diadelphia (stamens diadelphous).

18. Polyadelphia (stamens polyadelphous).

19. Syngenesia (stamens syngenesious).

20. Gynandria (stamens adnate to the pistil).

21. Monoecia (plants monoecious).

22. Dioecia (plants dioecious).

23. Polygamia (plants polygamous).

24. Cryptogamia (non-flowering plants i.e., cryptogams which include algae, fungi, mosses and ferns).

Due to simple and convenient approach, the Sexual System became very popular for more than 75 years before the publication of natural system by A. L. de Jussieu and A. P. de Candolle.

The merits and demerits of the Linnaeus system are:

Merits and Demerits:

Merit:

The only merit of this system is the quick and easy identification of plants based on one or a few characteristics.

Demerits:

1. The system is not at all sexual in proper sense, but based only on numerical relationship of sex organs. Thus, it can be said that this system was developed on differences rather than on similarities of sex organs.

2. The closely related members go apart and the distantly related members become very close to each other for the numerical relation of the sex organs.

3. The Gymnosperms were placed in the 14th class Didynamia along with Labiatae, an angiosperm family.

4. The Monocotyledons, Dicotyledons and Gymnosperms i.e., phanerogamic plants are not considered separately. Thus, the members of Dicotyledons and Monocoty­ledons become very close, e.g.,

i. In the 1st class Monandria (flower having 1 stamen) – Globba (Zingiberaceae of Monocotyledons) and Mangifera (Anacardiaceae of Dicotyledons).

ii. In the 6th class Hexandria (flowers having 6 stamens) -Alisma (Alismaceae of Monocotyledons) and Rumex (Polygonaceae of Dicoty­ledons) come very close. Many other examples are also available.

Benson (1957) made the comment that “certainly it did not contribute anything directly to knowledge of plant relationships, but it did give a tremendous impetus to study of plant kingdom”.

5. Thus it can be said that this classifica­tion is just like a dictionary where the words are arranged alphabetically with­out maintaining any relationship.

Natural system of classification:

This type of classification is based on the proper utilisation of all facts and figures avai­lable in nature. Based on common natural characteristics, the plants are grouped and placed into different taxa like classes, orders, families and genera. This type of system does not consider the evolutionary sequence and, hence, the affinity and relationship between the taxa are not considered.

The natural system of classification serves the practical need of easy identification.

Perhaps Michel Adanson (1727-1806) is the first person to reject all the artificial systems and propose his classification in favour of natural system. He was a French botanist and published his work in Families de Plantes (1763) in two volumes. His grouping of the plants is equivalent to orders and families of the modern system.

Later on, many botanists published (name of the publication with year is given in parentheses) their system and some of them are:

1. Antoine Laurent de Jussieu;

2. Augustin Pyramus de Candolle. In this book he proposed his approach to classify the plants. Later on, he published his work in Prodromus Systematis Naturalis Regni Vegetabilis. The first volume appeared in 1824 and was able to complete only 7 volumes during his life time. Later on his son Alphonse de Candolle published the rest in 10 volumes and the last one appeared in 1844.

3. Robert Brown;

4. John Lindley;

5. Stephan Endlicher;

6. George Bentham and Joseph Dalton Hooker.

Out of many natural systems proposed so far the system of classification of Bentham and Hooker gained the maximum popularity.

Botanist # 4. George Bentham (1800-1884) and Joseph Dalton Hooker’s (1817-1911) System:

Both the British botanists (Fig. 4.17, 4.18) were associated with the Royal Botanic Garden, Kew, England. They worked together for about 25 years and jointly published their work in Genera Plantarum (1862-1883) in 3 volumes. The 1st volume was published in July 1862 and the 3rd volume in April 1883. They described every species available at that time.

Robert Brown held that “Their Genera Plantarum was at that time a near approach to finality. Hitherto its supremacy has not been challenged”.

Their system was preferred by Britain and Commonwealth countries but not in Europe and North America, where Engler’s system is preferred.

They divided the seed plants into two Subkingdoms: Cryptogamia and Phanerogamia. The Phanerogamia was divided into two Divisions: Gymnospermae and Angiospermae. The Angiospermae was further divided into two Classes Dicotyledons and Monocotyledons.

The Dicotyledons was further divided into three subclasses Polypetalae, Gamopetalae and Monochlamydeae. Polypetalae was divided into three Series: Thalamiflorae, Disciflorae and Calyciflorae; Gamopetalae was divided into three Series: Inferae, Heteromerae and Bicarpellatae; Monochlamydeae into eight Series and the Class Monocotyledons was divided into seven Series.

The Series were further divided into Cohorts (= Orders), Cohorts into Natural Orders (= Families), Natural orders into Genera and, finally, Genera into Species.

They have placed Gymnospermae, in between Dicotyledons and Monocotyledons. According to their system, Dicotyledons starts with the Natural Order Ranunculaceae and ends in Ceratophyllaceae. On the other hand, Monocotyledons starts with the Natural Order Hydrocharitaceae and ends in Gramineae.

Merits and Demerits:

Merits:

1. This is a great natural system of its own kind.

2. This one is suitable for all practical pur­poses especially for identification and description of plants.

3. Beginning of the Subclass Polypetalae with the Cohort (= Order) Ranales, com­prised of Ranunculaceae and its allied Natural Orders (= Families).

4. The Dicotyledons are primitive than Monocotyledons.

5. They have studied the actual specimens available at that time and represented them in the classification after careful comparative examination.

Demerits:

1. The classification is based on the assumption of constancy of species. Hence, closely related Cohorts (= Orders) are often widely separated.

2. Authors were silent about the phylogeny of Dicotyledons and Monocoty­ledons and the anomalous position of Gymnosperms in between Dicoty­ledons and Monocotyledons.

3. The authors did not consider the phylogenetic relationship. Thus closely rela­ted Natural Orders (= Families) were placed apart and unrelated Natural Orders were placed very near. In Dicotyledons, Euphorbiaceae was placed in Monochlamydeae though it is related to Malvaceae of Polypetalae.

The Natural Orders like Polygonaceae, Nyctaginaceae, Amaranthaceae, Chenopodiaceae etc. are grouped together and placed under the Subclass Mono­chlamydeae which is also unnatural, because the above Natural Orders are related with the orders having differen­tiated perianth.

4. In Monocotyledons, they placed Scitamineae and Orchidaceae at the very beginning. But these should not be regarded as primitive with so many advanced characteristics.

5. In the Class Monocotyledons proper emphasis has not been given on:

i. The relative position of ovary, and

ii. Characteristics of the perianth.

Based on the above, it was considered that Iridaceae and Amaryllidaceae are more nearly related to Liliaceae than Scitamineae or Bromeliaceae which are associated for epigynous flowers. Hydrocharideae, though having inferior ovary, were placed nearer to aquatic cohorts with non-endospermic seeds.