Classification: relative merits and demerits of major systems of classifications - Engler & Prantle, Cronquist and Takhtajan

Classification: relative merits and demerits of major systems of classifications - Engler & Prantle, Cronquist and Takhtajan:-

Engler and Prantl Classification System:-

> The best known and widely accepted phylo­genetic system is that by Adolf Engler, Professor of Botany, University of Berlin. In 1892, he pub­lished a system of classification mainly based on August Wilhelm Eichler in the book ‘Syllabus der Vorlesungen’ as a guide to study the plants avai­lable in the Breslau Botanic Garden.

> During 1887-1915, Engler and his associate Karl Prantl made a monographic work, the “Die naturlichen Pflanzenfamilien” in 20 volumes, including all the known genera of plants from algae to the phanerogams along with key to identify the plants.

> Engler, in collaboration with Gilg, and later with Diels, published the works in a single volume ‘Syllabus der Pflanzenfamilien’. After his death, the book was revised by followers in several editions and the latest (12th) one in 2 volumes in 1954 and 1964.

> The system of Engler has been widely used in the American and Europian continents. Engler divided the plant kingdom into thir­teen (13) Divisions.

Merits:-

i. The entire Plant Kingdom was broadly treated with excellent illustrations, and phylogenetic arrangement of many groups of plants was made.

ii. The amalgamation of Polypetalae and Monochlamydeae into Archichlamy­deae is justified.

iii. Consideration and placing of Orchidaceae at the end of Monocotyledons and Compositae at the end of Dicoty­ledons are justified — since they are most highly evolved.

iv. Juncaceae, Amaryllidaceae and Iridaceae are placed judiciously nearer to Liliaceae.

Demerits:-

i. The placement of Amentiferae and Centrospermae almost at the beginning of Dicotyledones, even before Ranales, are not justified.

ii. The assemblage of all sympetalous mem­bers under Metachlamydeae increased the distance of closely related orders.

iii. The placing of Monocotyledons before Dicotyledons is not appropriate, because it is generally agreed that monocots have arisen from dicoty­ledons by reduction.

iv. The placing of the order Helobiae between the advanced orders Pandanales and Glumiflorae is questionable. Araceae was placed much earlier than Liliaceae, from which it has been derived.

v. Fossil evidences gave little support to this system.

Cronquist Classification System:-

> Arthur Cronquist was the Senior Curator of New York Botanic Garden and Adjunct Professor of Columbia University. He presented an elabo­rate interpretation of his concept of classification in “The Evolution and Classification of Flowering Plants”(1968). The further edition of his classi­fication was published in “An Integrated System of Classification of Flowering Plants” (1981).

> The latest revision was published in the 2nd edition in 1988 in “The Evolution and Classification of Flowering Plants”. He discussed a wide range of characteristics important to phylogenetic system. He also provided synoptic keys designed to bring the taxa in an appropriate alignment.

> He also represented his classification in charts to show the relationships of the orders within the various subclasses. His system is more or less parallel to Takhtajan’s system, but differs in details.

Merits:- 

i. There is general agreement of Cronquist’s system with that of other contemporary systems like Takhtajan, Dahlgren and Thorne.

ii. Detailed information on anatomy, ultra- structure phytochemistry and chromo­some — besides morphology — was presented in the revision of the classi­fication in 1981 and 1988.

iii. The system is highly phylogenetic.

iv. Nomenclature is in accordance with the ICBN.

v. The family Asteraceae in Dicotyledons and Orchidaceae in Monocotyledons are generally regarded as advanced and are rightly placed towards the end of respective groups.

vi. The relationships of different groups have been described with diagrams which provide valuable information on relative advancement and size of the various subclasses.

vii. The family Winteraceae (vessel-less wood present similar to Pteridosperms) placed at the beginning of dicotyledons is favoured by many authors.

viii. The subclass Magnoliidae is considered as the most primitive group of Dicotyledons. The placement of Dicotyledons before Monocotyledons finds general agreements with modern authors.

ix. As the text is in English, the system has been readily adopted in different books.

Demerits:-

i. Though highly phylogenetic and popu­lar in U.S.A., this system is not very use­ful for identification and adoption in Herbaria since Indented keys for genera are not provided.

ii. Dahlgren (1983, 89) and Thorne (1980, 83) treated angiosperms in the rank of a class and not that of a division.

iii. Superorder as a rank above order has not been recognised here, though it is present in other contemporary classifi­cations like Takhtajan, Thorne and Dahlgren.

iv. The subclass Asteridae represents a loose assemblage of several diverse sympetalous families.

v. Ehrendorfer (1983) pointed out that the subclass Hamamelidae does not represent an ancient side branch of the subclass Magnoliidae, but is remnant of a transition from Magnoliidae to Dilleniidae, Rosidae, and Asteridae.

vi. There is a difference in opinion with other authors regarding the systematic position of some orders like Typhales, Arales, Urticales etc.

Takhtajan Classification System:-

> Takhtajan was a reputed palaeobotanist of Komarov Botanical Institute of Leningrad, U.S.S.R. (now in Russia). He also made great contributions in the field of angiosperm taxo­nomy. In 1942, he proposed preliminary phylo­genetic arrangement of the orders of higher plants, based on the structural types of gynoecium and placentation.

> After 12 years i.e., in 1954, the actual system of classification was published in “The Origin of Angiospermous Plants” in Russian language. It was translated in English in 1958. Later on, in 1964, he proposed a new sys­tem in Russian language. To trace the evolution of angiosperm, he was particularly inspired by Hallier’s attempt to develop a synthetic evolu­tionary classification of flowering plants based on Darwinian philosophy.

> The classification was published in ‘Flowering Plants: Origin and Dispersal’ (1969) in English language. Later on, in 1980, a new revision of his system was pub­lished in “Botanical Review”.

> Takhtajan (1980) included the angiospermic plants under the Division Magnoliophyta. The Magnoliophyta is divided into two classes Magnoliopsida (Dicotyledons) and Liliopsida (Monocotyledons). The class Magnoliopsida consists of 7 subclasses, 20 superorders, 71 orders and 333 families.

> On the other hand, Liliopsida comprises of 3 subclasses, 8 super- orders, 21 orders and 77 families. The class Magnoliopsida starts with the order Magnoliales and ends in Asterales and the class Liliopsida begins with Alismatales and ends in Arales.

Merits:-

i. The classification of Takhtajan is more phylogenetic than that of earlier sys­tems.

ii. This classification is in a general agree­ment with the major contemporary systems of Cronquist, Dahlgren, Thorne, and others. Both phylogenetic and phenetic informations were adopted for delimination of orders and families.

iii. Due to the abolition of several artificial groups like Polypetalae, Gamopetalae, Lignosae, Herbaceae, many natural taxa came close together, viz. Lamiaceae (earlier placed under Herbaceae) and Verbenaceae (placed under Lignosae) are brought together under the order Lamiales.

iv. Nomenclature adopted in this system is in accordance with the ICBN, even at the level of division.

v. The treatment of Magnoliidae as a primitive group and the placement of Dicotyledons before Monocotyledons are in agreement with the other con­temporary systems.

vi. The derivation of monocots from the extinct terrestrial hypothetical group of Magnoliidae is found to be logical.

Demerits:-

i. In this system, more weightage is given to cladistic information in comparison to phenetic information.

ii. This system provides classification only up to the family level, thus it is not suitable for identification and for adop­tion in Herbaria. In addition, no key has been provided for identification of taxa.

iii. Takhtajan recognised angiosperms as division which actually deserve a class rank like that of the systems of Dahlgren (1983) and Throne (2003).

iv. Numerous monotypic families have been created in 1997 due to the further splitting and increase in the number of families to 592 (533 in 1987), resulting into a very narrow circumscription.

v. Takhtajan incorrectly suggested that smaller families are more “natural”.

vi. Although the families Winteraceae and Canellaceae showed their 99-100% relationship by multigene analyses, Takhtajan placed these two families in two separate orders.