Comparative account of various systems of Angiosperm Classification

Taxonomy began with man’s purely utilitarian interest in the flora of the earth. It grew with apparent observations of the various types of plants and their relationship which were, of course, based on the studies made by unaided eyes.

The word taxonomy was introduced by A.R de Candolle to designate the theory of plant classification. It has summoned innumerable people of the world since times gone by. It led to the systematic grouping of plants.

Classification is the inclusion of a plant or plants in categories based on a definite system and also according to the rules of International Code of Botanical Nomenclature (ICBN).

Aristotle and Theophrastus may be regarded as the two intellectual giants who infused life in plant taxonomy. The history of classification may be divided into ancient, middle and modern ages.

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There are various systems of classification:

(A) Artificial System:

According to this system, plants are classified on the basis of one or few convenient characteristics, e.g.

(1) Theophrastus (370 BC-285 BC), Father of Botany, ancient ages) in his book ‘Historia Plantarum’ classified about 480 plants into Trees, Shrubs, Undershrubs and Herbs.

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(2) Linnaeus (1707-1778, Middle ages): Carious Linnaeus called ‘father of plant taxonomy’ described a sexual system of plant classification, details of which were published in ‘Species Plantarum’ (1753). He took into consideration, the nature and number of stamens and carpels.

(B) Natural System (Modern Classification):

According to this system, overall resemblance (all important characters of plants are taken into consideration.

Bentham & Hooker (1862-1883) gave most important system of classification of angiosperms and published in three volumes of ‘Genera Plantarum’. They described 202 families.

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Bentham & Hooker divided plant kingdom into two subkingdoms.

Subkingdom 1: Cryptogamia-it includes non- flowering plants.

Subkingdom 2: Phanerogamia-it includes flowering plants.

This subkingdom 2 includes:

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(1) Class Dicotyledonae

(2) Class Gymnospermae

(3) Class Monocotyledonae

(1) Class Dicotyledonae : It is further divided into three subclasses

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(i) Subclass Polypetalae Petals free.

Series (A) Thalamiflorae:

Petals & stamens are hypogynous.

Order 1: Ranales: Families 8

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(a) Rununculaceae (b) Dilleniaceae

(e) Anonaceae (f) Magnoliaceae

(g) Berberidaceae (h) Nymphaceae.

Order 2: Perietales: Families 9

(a) Sarraceniaceae (b) Papaveraceae

(e) Resedaceae (f) Cistineae

(g) Violaceae (h) Canellaceae

(i) Bixineae.

Order 3: Polygalinae: Families 4

(a) Pittosporeae (b) Tremandreae

Order 4: Caryophyllineae : Families 4

(a) Frankeniaceae (b) Caryophyllaceae

Order 5: Guttiferales : Families 6

(a) Elatineae (b) Hypericineae

(e) Dipterocarpaceae (f) Chlaenaceae.

Order 6: Malvales : Families 3

(a) Malvaceae (b) Sterculiaceae

Series (B) Disciflorae:

The sepals are free or fused. These sepals are fused with ovary or free. A fleshy disc is found below ovary. Sometimes this disc is divided into some small glands. Here ovary is superior.

Order 7: Geraniales: Families 10

(a) Lineae (b) Humiriaceae

(e) Geraniaceae (f) Rutaceae

(g) Simarubeae (h) Ochnaceae

(i) Burseraceae (J) Meliaceae

(k) Chailletiaceae.

Order 8: Olacales: Families 3

(a) Olacineae (b) Ilicineae

Order 9: Celastrales: Families 4

(a) Celastrineae (b) Rhamnaceae

Order 10: Sapindales: Families 5

(a) Sapindaceae (b) Sabiaceae (c) Anacardiaceae

(d) Coriarieae (e) Moringeae.

Series (C) Calyciflorae:

Sepals are fused or free (sometimes) They are fused with ovary. Sepals are arranged in one or two whorls. Ovary is usually inferior.

Order 11: Rosales: Families 9

(a) Connaraceae (b) Leguminosae

(i) Papilionaceae

(ii) Caesapinioideae

(iii) Mimosoideae

(e) Craunulaceae (f) Droseraceae

(g) Hamamelidaceae (h) Bruniaceae

(i) Haloragaceae.

Order 12: Myrtales : Families 6

(a) Rhizophoraceae (b) Combretaceae

(e) Lythraceae (f) Onagraceae.

Order 13: Passiflorales: Families 7

(a) Samydaceae (b) Loaseae (c) Turneraceae

(d) Passifloraceae (e) Cucurbitaceae

(f) Begoniaceae (g) Datisceae.

Order 14: Ficoidales: Families 2

(a) Cactaceae (b) Ficoideae.

Order 15: Umbellales: Families 3

(a) Umbelliferae (b) Cornaceae (c) Araliaceae.

(ii) Subclass Gamepetalae:

The petals are fused. Stamens are usually epipetalous. Carpel may be syncarpour or apocarpous.

Series (A) Inferae:

Overy is inferior and stamen usually equal to petal lobes.

Order 1: Rubiales: Families 2

(a) Caprifoliaceae (b) Rubiaceae

Order 2: Asterales: Families 4

(a) Valerianeae (b) Dipsaceae

Order 3: Campanales: Families 3

(a) Stylidieae (b) Goodenovieae

Series (B) Heteromerae:

Order 4: Ericales : Families 6

(a) Ericaceae (b) Vacciniaceae

(e) Diapensiaceae if) Lennoaceae.

Order 5: Primulales : Families 3

(a) Plumbagineae (b) Primulaceae

Order 6: Ebenales : Families 3

(a) Sapotaceae (b) Ebenaceae

Series (C) Bicarpellate:

Ovary is superior. Stamens are usually equal to corolla lobes or lesser in number. Stamens are alternate to petals. Carpels are usually two, sometimes they may be lesser or more than two.

Order 7: Gentianales: Families 6

(a) Oleaceae (b) Salvadoraceae

(e) Loganiaceae (f) Gentianceae.

Order 8: Polemonials: Families 5

(a) Polemoniaceae (b) Hydrophyllaceae

Order 9: Personates: Families 8

(a) Scrophulariaceae (b) Orobanchaceae

(e) Gesneraceae (f) Bignoniaceae

(g) Pedaliaceae (h) Acanthaceae.

Order 10: Lamiales: Families 5

(a) Myoporineae (b) Selagineae

(e) Plantaginaceae (Anomalous family)

(iii) Subclass Monochlamydae:

Incomplete- In flowers perianth is in one whorl. Sometimes perianth may be absent. This subclass is divided into 8 series.

Series (A) Curvembrayae: Families 6

(a) Nyctaginaceae (b) Illecebraceae

(e) Phytolaccaceae (f) Batideae (g) Polygonaceae.

Series (B) Multiovulate Aquaticae: Family 1

(a) Podostemaceae Series (C) Multiovulate Terrestres: Families 3

(a) Nepenthaceae (b) Aristolochiaceae (c) Cytinaceae.

Series (D) Microembryeae: Families 4

(a) Piperaceae (b) Chloranthaceae

Series (E) Damphnales: Families 5

(a) Laurineae (b) Protecaceae

Series (F) Achlamydosporeae: Families 3

(a) Loranthaceae (b) Santalaceae (c) Balanophoreae.

Series (G) Unisexuales: Families 9

(a) Euphorbiaceae (b) Balanopseae

(e) Leitnerieae (f) Juglandaceae

(g) Myricaceae (h) Casuarinaceae (i) Cupuliferae.

Series (H) Ordines Anomali: Families 4

(a) Salicaceae (b) Empetraceae

(2) Class Gymnospermae: Families 3

(a) Gnetaceae (b) Coniferaceae

(3) Class Monocotyledonae:

Series (A) Microspermae: Families 3

(a) Hydrocharidaceae (b) Burmanniaceae (c) Orchidaceae.

Series (B) Epigynae: Families 7

(a) Scitamineae (b) Bromeliaceae

(e) Amaryllidaceae (f) Taccaceae (g) Dioscoreaceae

Series (C) Coronaireae: Families 8

(a) Roxburgluaceae (b) Liliaceae

(e) Xyrideae (f) Mayaceae

(g) Commelinaceae (h) Repateaceae.

Series (D) Calycineae: Families 3

(a) Flagellarieae (b) Juncaceae (c) Palmae.

Series (E) Nudiflorae: Families 5

(a) Pandanceae (b) Cyclanthaceae

(e) Lemnaceae.

Series (F) Apocarpae: Families 3

(a) Triurideae (b) Alismaceae

Series (G) Glumaceae: Families 5

(a) Eriocauleae (b) Centrolepideae

(e) Gramineae.

(C) Phylogenetic System:

These systems are based on evolutionary and genetical tendancies of plants. Some of the important phylogenetic systems are as follows:

(1) Engler & Prantl (1884-1930):

They formulated a detailed classification and published in 23 volumes of “Die Nuturlichen Pflanzen Families”.

(2) Hutchinson (1959):

He published a book ‘Families of flowering plants’in two volumes. (Vol. I. Dicotyledons, Vol. II. Monocotyledons.)

He divided angiosperms into 411 families.

(i) Dicotyledonae Groups

Division 1: Lignosae-246 families

Division 2: Herbacae-96 families

(ii) Monocotyledonae Groups

(a) Calyciflorae

(b) Corolliflorae

(3) A.L. Takhtajan (1967):

In his book “A System of Phylogeny of Flowering Plants” classified Angiosperms (Magnoliophyta). The outline of his classification is as follows:

Division:Magnoliophyta or Angiospermae

Class: Magnoliatae (or Dicotyledons)

Divided into: 7 subclasses

15 super orders

20 orders.

Class: Liliatae or Monocotyledons

Divided into 4 subclasses

5 super orders

20 orders.

Units of Classification:

In the modern classification, plant kingdom is divided in certain phyla. Each phylum is divided into classes. (Here phylum Anthophyta is taken as an example).

Phylum:

Whole of plant kindgom is divided into 25 phyla. The suffix of a phylum in either-ophyta or mycoty. Last phylum in Anthophyta.

Class:

Each phylum is divided into classes. Its suffix is usually -ae. The phylum Anthophyta has only a single class Angiospermae.

Subclass:

In modern classification, class is further divided into subsclass e.g. class Angiospermae in divided into two subclasses Dicotyledonae & Monocotyledonae.

Series:

Subclass is divided into more than one series.

Order:

This is the main part of the classification. Its suffix is -ales. In each order one or more families are included on the basis of similarities and dissimilarities in their specific characters.

Family:

This is smaller and important unit of taxon, in which plants of one or more than one genera are included. Its suffix is -aceae.

Genus:

Each family has one or more than one genera. Generic nomenclature is important.

Species:

This is the smallest unit of taxonomical classification. Its first letter is denoted with small letter.