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Selected Families of Angiosperms

Dicot Families

Family: Fabaceae (Pea family)

Systematic Position

General Characters

Distribution:
Fabaceae includes about 741 genera and more than 20, 200 species. The members are cosmopolitan in distribution but abundant in tropical and subtropical regions.

Habit:
All types of habits are represented in this family. Mostly herbs (Crotalaria), prostrate (Indigofera enneaphylla) erect (Crotalaria verrucosa), shrubs (Cajanus cajan), small trees (Sesbania), climbers (Clitoria), large tree (Pongamia, Dalbergia), woody climber (Mucuna), hydrophyte (Aeschynomene aspera) commonly called pith plant.

Root:
Tap root system, roots are nodulated, have tubercles containing nitrogen – fixing bacteria (Rhizobium leguminosarum)

Stem:
Aerial, herbaceous, woody (Dalbergia) twining or climbing (Clitoria).

Leaf:
Leaf simple or unifoliate (Desmodium gangeticum) bifoliate (Zornia diphylla,), Trifoliate (Lablab purpureus), alternate, stipulate, leaf base, pulvinate, reticulate venation terminal leaflet modifies into a tendril in Pisum sativum.

Inflorescence:
Raceme (Crotalaria verrucosa), panicle (Dalbergia latifolia) axillary solitary (Clitoria ternatea)

Flowers:
Bracteate, bracteolate, pedicellete, complete, bisexual, pentamerous, heterochlamydeous, zygomorphic hypogynous or sometimes perigynous.

Calyx:
Sepals 5, green, synsepalous, more or less united in a tube and persistant, valvate or imbricate, odd sepal is anterior in position.

Corolla:
Petals 5, apopetalous, unequal and papilionaceous, vexillary or descendingly imbricate aestivation, all petals have claw at the base. The outer most petal is large called standard petal or vexillum, Lateral 2 petals are lanceolate and curved. They are called wing petals or alae. Anterior two petals are partly fused and are called keel petals or carina which encloses the stamens and pistil.

Androecium:
Stamens 10, diadelphous, usually 9+1 (Clitoria ternatea). The odd stamen is posterior in position. In Aeschynomene aspera, the stamens are fused to form two bundles each containing five stamens (5)+(5). Stamens are monadelphous and dimorphic ie. 5 stamens have longer filaments and other 5 stamens have shorter filaments thus the stamens are found at two levels and the shape of anthers also varies in (Crotalaria verrucosa). (5 anthers are long and lanceolate, and the other 5 anthers are short and blunt). Anthers are dithecous, basifixed and dehiscing longitudinally

Gynoecium:
Monocarpellary, unilocular, ovary superior, with two alternating rows of ovules on marginal placentation. Style simple and bent, stigma flattened or feathery.

Fruit:
The characteristic fruit of Fabaceae is a legume (Pisum sativum), sometimes indehiscent and rarely a lomentum (Desmodium). In Arachis hypogea the fruit is geocarpic (fruits develops and matures under the soil). After fertilization the stipe of the ovary becomes meristematic and grows down into the soil. This ovary gets buried into the soil and develops into fruit.

Seed:
Endospermic or non-endospermic (Pisum sativum), mostly reniform.

Botanical Description of Clitoria Ternatea (Sangu Pushpam)

Habit:
Twining climber

Root:
Branched tap root system having nodules.

Stem:
Aerial, weak stem and a twiner

Leaf:
Imparipinnately compound, alternate, stipulate showing reticulate venation. Leaflets are stipellate. Petiolate and stipels are pulvinated.

Inflorescence:
Solitary and axillary

Flower:
Bracteate, bracteolate, bracteoles usually large, pedicellate, heterochlamydeous, complete, bisexual, pentamerous, zygomorphic and hypogynous.

Calyx:
Sepals 5, synsepalous, green showing valvate aestivation. Odd sepal is anterior in position.

Corolla:
Petals 5, white or blue apopetalous, irregular papilionaceous corolla showing descendingly imbricate aestivation.

Androecium:
Stamens 10, diadelphous (9)+1, nine stamens fused to form a bundle and the tenth stamen is free. Anthers are dithecous, basifixed, introse and dechiscing by longitudinal slits.

Gynoecium:
Monocarpellary, unilocular, with many ovules on mariginal placentation, ovary superior, style simple and incurved with feathery stigma.

Fruit:
Legume

Seed:
Non-endospermous, reniform.

Floral Formula:

Economic Importance

Family:
Solanaceae (Potato Family / Night shade family)

Systematic Position

General Characters

Distribution:
Family Solanaceae includes about 88 genera and about 2650 species, of these Solanum is the largest genus of the family with about 1500 species. Plants are worldwide in distribution but more abundant in South America.

Habit:
Mostly annual herbs, shrubs, small trees (Solanum violaceum) lianas with prickles (Solanum trilobatum)

Root:
Branched tap root system.

Stem:
Herbaceous or woody; erect or twining, or creeping; sometimes modified into tubers (Solanum tuberosum) it is covered with Spines (Solanum tuberosum)

Leaves:
Alternate, simple, rarely pinnately compound (Solanum tuberosum and Lycopersicon esculentum, exstipulate, opposite or sub-opposite in upper part, unicostate reticulate venation. Yellowish verbs present in Solanum tuberosum.

Inflorescence:
Generally axillary or terminal cymose (Solanum) or solitary flowers (Datura stramonium). Extra axillary scorpiod cyme called rhiphidium (Solanum americanum) solitary and axillary (Datura and Nicotiana) umbellate cyme (Withania somnifera).

Flowers:
Bracteate or ebracteate, pedicellate, bisexual, heterochlamydeous, pentamerous actinomorphic or weakly zygomorphic due to oblique position of ovary, hypogynous.

Calyx:
Sepals 5, Synsepalous, valvate persistent (Solanum americanum), often accrescent. (Physalis)

Corolla:
Petals 5, sympetalous, rotate, tubular (Solanum) or bell – shaped (Atropa) or infundibuliform (Petunia) usually alternate with sepals; rarely bilipped and zygomorphic (Schizanthus) usually valvate, sometimes convolute (Datura).

Androecium:
Stamens 5, epipetalous, filaments usually unequal in length, stamens only 2 in Schizanthus (others 3 are reduced to staminode), Anthers dithecous, dehisce longitudinally or poricidal.

Gynoecium:
Bicarpellary, syncarpous obliquely placed, ovary superior, bilocular but looks tetralocular due to the formation of false septa, numerous ovules in each locule on axile placentation.

Fruit:
A capsule or berry. (Datura & Petunia, Lycopersicon esculentum, Capsicum)

Seed:
Endospermous.

Botanical Description of Datura Metel

Habit:
Large, erect and stout herb.

Root:
Branched tap root system.

Stem:
Stem is hollow, green and herbaceous with strong odour.

Leaf:
Simple, alternate, petiolate, entire or deeply lobed, glabrous exstipulate showing unicostate reticulate venation.

Inflorescence:
Solitary and axillary cyme.

Flower:
Flowers are large, greenish white, bracteate, ebracteolate, pedicellate, complete, heterochlamydeous, pentamerous, regular, actinomorphic, bisexual and hypogynous.

Calyx:
Sepals 5, green synsepalous showing valvate aestivation. Calyx is mostly persistent, odd sepal is posterior in position.

Corolla:
petals 5, greenish white, sympetalous, plicate (folded like a fan) showing twisted aestivation, funnel shaped with wide mouth and 10 lobed.

Androecium:
Stamens 5, free from one another, epipetalous, alternipetalous and are inserted in the middle of the corolla tube. Anthers are basifixed, dithecous, with long filament, introse and longitudinally dehiscent.

Gynoecium:
Ovary bicarpellary, syncarpous superior ovary, basically bilocular but tetralocular due to the formation of false septum. Carpels are obliquely placed and ovules on swollen axile placentation. Style simple long and filiform, stigma two lobed.

Fruit:
Spinescent capsule opening by four apical valves with persistent calyx.

Seed:
Endospermous.

Floral Formula:

Economic Importance of the Family Liliaceae

Family: Liliaceae (Lily Family)

Systematic Position

General Characters

Distribution:
Liliaceae are fairly large family comprising about 15 genera and 550 species. Members of this family are widely distributed over most part of the world.

Habit:
Mostly perennial herbs persisting by means of a sympodial rhizome (Polygonatum), by a bulb (Lilium) corm (Colchicum), shrubby or tree like (Yucca and Dracaena) oody climbers, climbing with the help of stipular tendrils in Smilax. Trees in (Xanthorrhoea), succulents (Aloe).

Root:
Adventitious and firous, and typically contractile.

Stem:
Stems usually bulbous, rhizomatous in some, aerial, erect (Dracaena) or climbing (Smilax) in Ruscus the ultimate branches are modified into phylloclades, In Asparagus stem is modified into cladodes and the leaves are reduced to scales.

Leaf:
Leaves are radical (Lilium) or cauline (Dracaena), usually alternate, opposite (Gloriosa), sometimes fleshy and hollow, reduced to scales (Ruscus and Asparagus). The venation is parallel but in species of Smilax it is reticulate. Leaves are usually exstipulate, but in Smilax, two tendrils arise from the base of the leaf, which are considered modified stipules.

Inflorescence:
Flowers are usually borne in simple or branched racemes (Asphodelus) spikes in Aloe, huge terminal panicle in Yucca, solitary and axillary in Gloriosa, solitary and terminal in Tulipa.

Flowers:
Flowers are often showy, pedicellate, bracteate, ebracteolate, except Dianella and Lilium, bisexual, actinomorphic, trimerous, hypogynous, rarely unisexual (Smilax) and are dioecious, rarely tetramerous (Maianthemum), slightly zygomorphic (Lilium) and hypogynous.

Perianth:
Tepals 6 biseriate arranged in two whorls of 3 each, apotepalous or rarely syntepalous as in Aloe. Usually petaloid or sometimes sepaloid, odd tepal of the outer whorl is anterior in position, valvate or imbricate, tepals more than six in Paris quadrifolia.

Androecium:
Stamens 6, arranged in 2 whorls of 3 each, rarely stamens are 3 (Ruscus), 4 in Maianthemum, or up to 12, apostamenous, opposite to the tepals, sometimes epitepalous; fiaments distinct or connate, anthers dithecous, basified or versatile, extrose, or introse, dehiscing usually by vertical slit and sometimes by terminal pores; rarely synstamenous (Ruscus).

Gynoecium:
Tricarpallary, syncarpous, the odd carpel usually anterior, ovary superior, trilocular, with 2 rows of numerous ovules on axile placextation. Style simple, slender with simple stigma.

Fruit:
A loculicidal capsule

Seed:
Endospermous

Floral Formula:

Economic Importance of the Family Liliaceae

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Cladistics and its Various Types of Classifications

Analysis of the taxonomic data, and the types of characters that are used in classification have changed from time to time. Plants have been classified based on the morphology before the advancement of microscopes, which help in the inclusions of sub microscopic and microscopic features.

A closer study is necessary while classifying closely related plants. Discovery of new fier molecular analytical techniques coupled with advanced software and computers has ushered in a new era of modern or phylogenetic classification.

The method of classifying organisms into monophyletic group of a common ancestor based on shared apomorphic characters is called cladistics (from Greek, kladosbranch).

The outcome of a cladistic analysis is a cladogram, a tree-shaped diagram that represent the best hypothesis of phylogenetic relationships. Earlier generated cladograms were largely on the basis of morphological characters, but now genetic sequencing data and computational softwares are commonly used in phylogenetic analysis.

Cladistic Analysis

Cladistics is one of the primary methods of constructing phylogenies, or evolutionary histories. Cladistics uses shared, derived characters to group organisms into clades.

These clades have atleast one shared, derived character found in their most recent common ancestor that is not found in other groups hence they are considered more closely related to each other. These shared characters can be morphological such as, leaf, flower, fruit, seed and so on; behavioural, like opening of flowers nocturnal/diurnal; molecular like, DNA or protein sequence and more.

Cladistics accept only monophyletic groups. Paraphyletic and polyphyletic taxa are occasionally considered when such taxa conveniently treated as one group for practical purposes. Example: dicots, sterculiaceae. Polyphyletic groups are rejected by cladistics.

(i) Monophyletic Group:
Taxa comprising all the descendants of a common ancestor.

(ii) Paraphyletic Group:
Taxon that includes an ancestor but not all of the descendants of that ancestor.

(iii) Polyphyletic Group:
Taxa that includes members from two different lineages.

Need for Cladistics

1. Cladistics is now the most commonly used and accepted method for creating phylogenetic system of classifications.
2. Cladistics produces a hypothesis about the relationship of organisms to predict the phylogeny
3. Cladistics helps to elucidate mechanism of evolution.

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Modern Trends in Taxonomy Differences and Classification

Taxonomists now accept that, the morphological characters alone should not be considered in systematic classification of plants. The complete knowledge of taxonomy is possible with the principles of various disciplines like Cytology, Genetics, Anatomy, Physiology, Geographical Distribution, Embryology, Ecology, Palynology, Phenology, Bio-Chemistry, Numerical Taxonomy and Transplant Experiments.

These have been found to be useful in solving some of the taxonomical problems by providing additional characters. It has changed the face of classification fromalpha (classical) toomega (modern kind). Thus the new systematic has evolved into a better taxonomy.

Chemotaxonomy

Proteins, amino acids, nucleic acids, peptides etc are the most studied chemicals in chemotaxonomy. Chemotaxonomy is the scientific approach of classification of plants on the basis of their biochemical constituents. As proteins are more closely controlled by genes and less subjected to natural selection, it has been used at all hierarchical levels of classification starting from the rank of ‘variety’ up to the rank of division in plants.

The chemical characters can be divided into three main categories:-

1. Easily visible characters like starch grains, silica.
2. Characters detected by chemical tests like phenolics, oil, fats, waxes.
3. Proteins.

Aims of Chemotaxonomy

1. To develop taxonomic characters which may improve existing system of plant classification.
2. To improve present day knowledge of phylogeny of plants.

Biosystematics

Biosystematics is an “Experimental, ecological and cytotaxonomy” through which life forms are studied and their relationships are defined. The term biosystematics was introduced by Camp and Gilly in 1943. Many authors feel Biosystematics is closer to Cytogenetics and Ecology and much importance given not to classification but to evolution.

Aims of Biosystematics

The aims of biosystematics are as follows:

1. To delimit the naturally occurring biotic community of plant species.
2. To establish the evolution of a group of taxa by understanding the evolutionary and phylogenetic trends.
3. To involve any type of data gathering based on modern concepts and not only on morphology and anatomy.
4. To recognize the various groups as separate biosystematic categories such as ecotypes, ecospecies, cenospecies and comparium.

Karyotaxonomy

Chromosomes are the carriers of genetic information. Increased knowledge about the chromosomes have been used for extensive biosystematic studies and resolving many taxonomic problems. Utilization of the characters and phenomena of cytology for the explanation of taxonomic problem is known as cytotaxonomy or karyotaxonomy. The characters of chromosome such as number, size, morphology and behaviour during meiosis have proved to be of taxonomic value.

Serotaxonomy (Immunotaxonomy)

Systematic serology or serotaxonomy had its origin towards the end of twentieth century with the discovery of serological reactions and development of the discipline of immunology. The classification of very similar plants by means of differences in the proteins they contain, to solve taxonomic problems is called serotaxonomy. Smith (1976) defined it as “the study of the origins and properties of antisera.”

Importance of Serotaxonomy

It determines the degree of similarity between species, genera, families etc. by comparing the reactions of antigens from various plant taxa with antibodies raised against the antigen of a given taxon.

Example:
1. The assignment of Phaseolus aureus and P. mungo to the genus Vigna is strongly supported by serological evidence by Chrispeels and Gartner.

Molecular Taxonomy (Molecular Systematics / Molecular Phylogenetics)

Molecular Taxonomy is the branch of phylogeny that analyses hereditary molecular differences, mainly in DNA sequences, to gain information and to establish genetic relationship between the members of different taxonomic categories.

The advent of DNA cloning and sequencing methods have contributed immensely to the development of molecular taxonomy and population genetics over the years. These modern methods have revolutionised the field of molecular taxonomy and population genetics with improved analytical power and precision.

The results of a molecular phylogenetic analysis are expressed in the form of a tree called phylogenetic tree. Different molecular markers like allozymes, mitochondrial DNA, microsatellites, RFLP (Restriction Fragment Length Polymorphism), RAPD (Random amplified polymorphic DNA), AFLPs (Amplified Fragment Length Polymorphism), single nucleotide polymorphism – (SNP), microchips or arrays are used in analysis.

Uses of Molecular Taxonomy

1. Molecular taxonomy helps in establishing the relationship of different plant groups at DNA level.
2. It unlocks the treasure chest of information on evolutionary history of organisms.

RFLP (Restriction Fragment Length Polymorphism)

RFLPs is a molecular method of genetic analysis that allows identification of taxa based on unique patterns of restriction sites in specific regions of DNA. It refers to differences between taxa in restriction sites and therefore the lengths of fragments of DNA following cleavage with restriction enzymes.

Amplified Fragment Length Polymorphism (AFLP)

This method is similar to that of identifying RFLPs in that a restriction enzyme is used to cut DNA into numerous smaller pieces, each of which terminates in a characteristic nucleotide sequence due to the action of restriction enzymes. AFLP is largely used for population genetics studies, but has been used in studies of closely related species and even in some cases, for higher level cladistic analysis.

Random Amplified Polymorphic DNA (RAPD)

It is a method to identify genetic markers using a randomly synthesized primer that will anneal (recombine (DNA) in the double stranded form) to complementary regions located in various locations of isolated DNA. If another complementary site is present on the opposing DNA strand at a distance that is not too great (within the limits of PCR) then the reaction will amplify this region of DNA.

RAPDs like microsatellites may often be used for genetic studies within species but may also be successfully employed in phylogenetic studies to address relationships within a species or between closely related species. However RAPD analysis has the major disadvantage that results are difficult to replicate and in that the homology of similar bands in different taxa may be nuclear.

Significance of Molecular Taxonomy

1. It helps to identify a very large number of species of plants and animals by the use of conserved molecular sequences.
2. Using DNA data evolutionary patterns of biodiversity are now investigated.
3. DNA taxonomy plays a vital role in phytogeography, which ultimately helps in genome mapping and biodiversity conservation.
4. DNA- based molecular markers used for designing DNA based molecular probes, have also been developed under the branch of molecular systematics.

DNA Barcoding

Have you seen how scanners are used in supermarkets to distinguish the Universal Product Code (UPC)? In the same way we can also distinguish one species from another. DNA barcoding is a taxonomic method that uses a very short genetic sequence from a standard part of a genome. The genetic sequence used to identify a plant is known as “DNA tags” or “DNA barcodes”. Paul Hebert in 2003 proposed ‘DNA barcoding’ and he is considered as ‘Father of barcoding’.

The gene region that is being used as an effective barcode in plants is present in two genes of the chloroplast, matK and rbcL, and have been approved as the barcode regions for plants. Sequence of unknown species can be matched from submitted sequence in GenBank using Blast (web-programme for searching the closely related sequence).

Significance of DNA Barcoding

1. DNA barcoding greatly helps in identification and classification of organism.
2. It aids in mapping the extent of biodiversity.

DNA barcoding techniques require a large database of sequences for comparison and prior knowledge of the barcoding region. However, DNA barcoding is a helpful tool to determine the authenticity of botanical material in whole, cut or powdered form.

Differences Between Classical and Modern Taxonomy

Classical Taxonomy	Modern Taxonomy
1. It is called old systematics or Alpha (α) taxonomy or Taxonomy	1. It is called Neosystematics Or Biosystematics or Omega (Ω) taxonomy
2. It is pre Darwinean	2. It is post Darwinean
3. Species is considered as basic unit and is static	3. Species is considered as dynamic entity and over changing

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Types of Classification and its Significance

Taxonomic entities are classified in three ways. They are artificial classification, natural classification and phylogenetic classification.

Artificial System of Classification

Carolus Linnaeus (1707 – 1778) was a great Swedish Botanist and said to be the “Father of Taxonomy.” He outlined an artificial system of classification in “Species Plantarum” in 1753, wherein he listed and described 7, 300 species and arranged in 24 classes mostly on the basis of number, union (adhesion and cohesion), length, and distribution of stamens. The classes were further subdivided on the basis of carpel characteristics into orders. Hence the system of classification is also known as sexual system of classification.

This system of classification though artificial, was continued for more than 100 years after the death of Linnaeus, due to its simplicity and easy way of identification of plants. However the system could not hold good due to the following reasons.

1. Totally unrelated plants were kept in a single group, whereas closely related plants were placed in widely separated groups.

Example:

a. Zingiberaceae of monocotyledons and Anacardiaceae of dicotyledonous were placed under the class Monandria since these possess single stamens.

b. Prunus was classified along with Cactus because of the same number of stamens. No attempts were made to classify plants based on either natural or phylogenetic relationships which exist among plant groups.

Natural System

Botanists who came after Linnaeus realised that no single character is more important than the other characters. Accordingly an approach to a natural system of classification sprouted in France. The first scheme of classification based on overall similarities was presented by Antoine Laurent de Jessieu in 1789.

Bentham and Hooker system of Classification

A widely followed natural system of classification considered the best was proposed by two English botanist George Bentham (1800 – 1884) and Joseph Dalton Hooker (1817 – 1911). The classification was published in a three volume work as “Genera Plantarum” (1862 – 1883) describing 202 families and 7569 genera and 97,205 species. In this system the seeded plants were classified into 3 major classes such as Dicotyledonae, Gymnospermae and Monocotyledonae.

Class I Dicotyledonae:
Plants contain two cotyledons in their seed, leaves with reticulate venation, tap root system and tetramerous or pentamerous flowers come under this class. It includes tree subclasses – Polypetalae, Gamopetalae and Monochlamydeae.

Sub-class 1.

Polypetalae:
Plants with free petals and dichlamydeous flowers come under polypetalae. It is further divided into three series – Thalamiflorae, Disciflorae and Calyciflorae.

Series (i) Thalamiflorae:
Plants having flowers with dome or conical shaped thalamus and superior ovary are included in this series. It includes 6 orders and 34 families.

Series (ii) Disciflorae:
Flowers having prominent disc shaped thalamus with superior ovary come under this series. It includes 4 orders and 23 families.

Series (iii) Calyciflorae:
It includes plants having flowers with cup shaped thalamus and with inferior or sometimes with half inferior ovary. Calyciflorae includes 5 orders and 27 families.

Sub-class 2.

Gamopetalae:
Plants with united petals, which are either partially or completely fused to one another and dichlamydeous are placed under Gamopetalae. It is further divided into three series – Inferae, Heteromerae and Bicarpellatae.

Series (i) Inferae:
The flowers are epigynous and with inferior ovary. Inferae includes 3 orders and 9 families.

Series (ii) Heteromerae:
The flowers are hypogynous, superior ovary and with more than two carpels. Heteromerae includes 3 orders and 12 families.

Series (iii) Bicarpellatae:
The flowers are hypogynous, superior ovary and with two carpels. Bicarpellatae includes 4 orders and 24 families.

Sub-class 3.

Monochlamydeae:
Plants with incomplete flowers either apetalous or with undifferentiated calyx and corolla are placed under Monochlamydeae. The sepals and petals are not distinguished and they are called perianth. Sometimes both the whorls are absent. Monochlamydeae includes 8 series and 36 families.

Class II Gymnospermae:
Plants that contain naked seeds come under this class. The Gymnospermae includes three families – Gnetaceae, Coniferae and Cycadaceae.

Class III Monocotyledonae:
Plants contain only one cotyledon in their seed, leaves with parallel venation, fibrous root system and trimerous flowers come under this class. The Monocotyledonae has 7 series and 34 families.

The Bentham and Hooker system of classification is still supposed to be the best system of classification. It has been widely practiced in colonial countries and herbaria of those countries were organised based on this system and is still used as a key for the identification of plants in some herbaria of the world due to the following reasons:

Description of plants is quite accurate and reliable, because it is mainly based on personal studies from actual specimens and not mere comparisons of known facts. As it is easy to follow, it is used as a key for the identification of plants in several herbaria of the world. Though it is a natural system, this system was not intended to be phylogenetic.

Phylogenetic System of Classification

The publication of the Origin of Species (1859) by Charles Darwin has given stimulus for the emergence of phylogenetic system of classification.

I. Adolph Engler and Karl A Prantl System of Classification

One of the earliest phylogenetic system of classification of the entire plant Kingdom was jointly proposed by two German botanists Adolph Engler ( 1844 -1930) and Karl A Prantl (1849 – 1893). They published their classification in a monumental work “Die Naturelichen Pflanzen Familien” in 23 volumes (1887 – 1915).

In this system of classifiation the plant kingdom was divided into 13 divisions. The first 11 divisions are Thllophytes, twelfth division is Embryophyta Asiphonogama (plants with embryos but no pollen tubes; Bryophytes and Pteridophytes) and the thirteenth division is Embryophyta Siphonogama (plants with embryos and pollen tubes) which includes seed plants.

II. Arthur Cronquist System of Classification Arthur Cronquist (1919 – 1992)

An eminent American taxonomist proposed phylogenetic classification of flowering plants based on a wide range of taxonomic characters including anatomical and phytochemical characters of phylogenetic importance.

He has presented his classification in 1968 in his book titled “The evolution and classification of flowering plants.” His classification is broadly based on the Principles of phylogeny that finds acceptance with major contemporary authors.

Cronquist classified the angiosperms into two main classes Magnoliopsida (=dicotyledons) and Liliopsida (=monocotyledons). There are 6 subclasses, 64 orders, 320 families and about 165,000 species in Magnoliopsida, whereas in Liliopsida there are 5 sub classes, 19 orders, 66 families and about 50,000 species.

Cronquist system of classification also could not persist for a long time because, the system is not very useful for identification and cannot be adopted in herbaria due to its high phylogenetic nature.

Angiosperm Phylogeny Group (APG) Classification

The most recent classification of flowering plants based on phylogenetic data was set in the last decade of twentieth century. Four versions of Angiosperm Phylogenetic Group classification (APG I, APG II, APG III & APG IV) have been published in 1998, 2003, 2009 and 2016 respectively.

Each version supplants the previous version. Recognition of monophyletic group based on the information received from various disciplines such as gross morphology, anatomy, embryology, palynology, karyology, phytochemistry and more strongly on molecular data with respect to DNA sequences of two chloroplast genes (atpB and rbcL) and one nuclear gene (nuclear ribosomal 18s DNA).

The most recent updated version, APG IV (2016) recognised 64 orders and 416 families. Of these, 416 families 259 are represented in India. The outline of APG IV classification is given below. Angiosperms are classified into three clades early angiosperms, monocots and eudicots. Early angiosperms are classified into 8 orders and 26 families (ANAclade + magnoliids + Chloranthales) Amborellales, Nymphaeale, Austrobaileyales.

• Seeds generally always with two cotyledons.
• Presence of ethereal oils.
• Leaves are always simple net-veined.
• Each floral whorls with many parts.
• Perianth usually spirally arranged or parts in threes.
• Stamens with broad filaments.
• Anthers tetrasporangiate.
• Pollen monosulcate.
• Nectaries are rare.
• Carpels usually free and
• Embryo very small.

Monocots are classified into 11 orders and 77 families (basal monocots + lilioids + commelinids)

• Seeds with single cotyledon.
• Primary root short-lived.
• Single adaxial prophyll.
• Ethereal oils rarely present.
• Mostly herbaceous, absence of vascular cambium.
• Vascular bundles are scattered in the stem.
• Leaf simple with parallel-veined.
• Floral parts usually in threes.
• Perianth often composed of tepals.
• Pollen monosulcate.
• Styles normally hollow and
• Successive microsporogenesis.

Eudicots are divided into 45 orders and 313 families (early diverging eudicots + super rosids + super asterids).

• Seeds with always two cotyledons.
• Nodes trilacunar with three leaf traces.
• Stomata anomocytic.
• Ethereal oils rarely present.
• Woody or herbaceous plants.
• Leaves simple or compound, usually netveined.
• Flower parts mostly in twos, fours or fives.
• Microsporogenesis simultaneous.
• Style solid and
• Pollen tricolpate.

APG system is an evolving system that might undergo change periodically based on the new sets of data from various disciplines of Botany.

It is the currently accepted system across the world and followed by all the leading taxonomic institutions and practising taxonomists. However, it is yet to percolate into the Indian botanical curriculum. Classification reflects the state of our knowledge at a given point of time. It will continue to change as we acquire new information.

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Need for Classification

Understanding the classification of organisms can give an insight into other fields and has significant practical value. Classification helps us to know about different taxa, their phylogenetic relationship and exact position.

It helps to train the students of plant sciences with regard to the diversity of organisms and their relationship with other biological branches. It helps us understand the inter-relationship among different groups of organisms.

To understand and study the features, similarities and differences between different living organisms and how they are grouped under different categories. It helps to know the origin and evolution of organisms.

It helps in identification of new organism. Classification helps in knowing the relationship amongst different groups of organisms. The organism of past cannot be studied without a proper system of classification.

It helps to understand how the different organisms have evolved with time. It helps to understand the relationships between different groups of organisms. It forms a base for the study of other biological sciences, like biogeography.

It enables chemists to predict the properties of the elements and their compounds based on their positions in the Periodic Table, and vice versa. It becomes easier to study, understand, compare and contrast the related properties among the elements and their compounds from different groups.

The advantages of classifying organisms are as follows:

1. Classification facilitates the identification of organisms
2. Helps to establish the relationship among various groups of organisms
3. Helps to study the phylogeny and evolutionary history of organisms.

Basis of Classification:
The characteristics based on which the living organisms can be classified.

Characteristic:
A distinguishing quality, trait or feature of an individual seen in all members of the same species.

There are three main types of classification-artifical, natural and phylogenetic:

• Artificial System of Classification.
• Natural System of Classification.
• Phylogenetic System of Classification.

The current taxonomic system now has eight levels in its hierarchy, from lowest to highest, they are: species, genus, family, order, class, phylum, kingdom, domain.

Classification is a process related to categorization, the process in which ideas and objects are recognized, differentiated and understood. See Classification (general theory).

Grouping of elements into different classes is called periodic classification of elements. This method is requires arranging the elements that are alike and separating the elements that are unlike. It helps us understand how different elements form different compounds.

A disadvantage to classification is that many of the classifications themselves are based on subjective judgments, which may or may not be shared by everyone participating. This would lead to differences in perceived value.

The definition of classifying is categorizing something or someone into a certain group or system based on certain characteristics. An example of classifying is assigning plants or animals into a kingdom and species. An example of classifying is designating some papers as “Secret” or “Confidential.”

Given a population whose members each belong to one of a number of different sets or classes, a classification rule or classifier is a procedure by which the elements of the population set are each predicted to belong to one of the classes.

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Classification of Plants

Imagine walking into a library and looking for a Harry Potter story book. As you walk into the library you notice that it is under renovation and all the books are scattered. Will it not be hard to find the exact book you are looking for? It might take hours. So you decide to come the next day when all the books are arranged according to the genres. One rack for adventure, another for Detective, Fantasy, Horror, Encyclopaedia and so on.

You automatically know Harry Potter is in the fantasy section and it takes less than ten minutes for you to find it. That is because the books have been classified and arranged according to a system. Similarly there is a vast assemblage of group of plants in the world. Is it possible to study and understand all of these? No Since it is difficult to study all these plants together, it is necessary to device some means to make this possible.

Classification is essential to biology because there is a vast diversity of organisms to sort out and compare. Unless they are organized into manageable categories it will be difficult for identification. Biological classifications are the inventions of biologists based upon the best evidence available. The scientific basis for cataloguing and retrieving information about the tremendous diversity of flora is known as classification.

Classification paves way for the arrangement of organisms into groups on the basis of their similarities, dissimilarities and relationships. The purpose of classification is to provide a systematic arrangement expressing the relationship between the organisms. Taxonomists have assigned a method of classifying organisms which are called ranks.

These taxonomical ranks are hierarchical. The scheme of classification has to be flexible, allowing newly discovered living organisms to be added where they fit best. While there are many ways to structure plant classification, one way is to group them into vascular and non-vascular plants, seed bearing and spore bearing, and angiosperms and gymnosperms. Plants can also be classified as grasses, herbaceous plants,
woody shrubs, and trees.

Classification is based on the following criteria: Plant body: Presence or absence of a well-differentiated plant body. E.g. Root, Stem and Leaves. Vascular system: Presence or absence of a vascular system for the transportation of water and other substances.

Within the plant kingdom, plants are divided into two main groups. These are flowering plants (angiosperms) and conifers, Ginkgos, and cycads (gymnosperms). The other group contains the seedless plants that reproduce by spores. It includes mosses, liverworts, horsetails, and ferns.

The major plant groups include bryophytes (mosses), pteridophytes (ferns), gymnosperms (conifers), and angiosperms (flowering, seed-bearing plants). Mosses are short plants and their leaves are usually only one cell thick. Ferns have many leaves branching out from their fronds.

Natural system of classification is that in which all natural characters of plants both vegetative and reproductive are taken in to consideration as the basic of classification principally the plants are grouped according to their related characters.

What are different types of flowers? They can be classified in many different ways: Based on presence or absence of seeds, Based on whether the plants produce flowers or not, Based on the presence of stems, leaves, and roots.

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Herbarium – Preparation and Uses

Herbaria are store houses of preserved plant collections. Plants are preserved in the form of pressed and dried specimens mounted on a sheet of paper. Herbaria act as a centre for research and function as sources of material for systematic work.

Preparation of Herbarium Specimen

Herbarium Specimen is defined as a pressed and dried plant sample that is permanently glued or strapped to a sheet of paper along with a documentation label. Preparation of herbarium specimen includes the following steps.

1. Plant Collection: Field collection, Liquid preserved collection, Living collection, Collection for molecular studies.
2. Documentation of field site data
3. Preparation of plant specimen
4. Mounting herbarium specimen
5. Herbarium labels
6. Protection of herbarium sheets against mold and insects

Uses of Herbarium

1. Herbarium provides resource material for systematic research and studies.
2. It is a place for orderly arrangement of voucher specimens.
3. Voucher specimen serves as a reference for comparing doubtful newly collected fresh specimens.
4. Voucher specimens play a role in studies like floristic diversity, environmental assessment, ecological mechanisms and survey of unexplored areas.
5. Herbarium provides opportunity for documenting biodiversity and studies related to the field of ecology and conservation biology.

Kew Herbarium

Kew Garden is situated in South West London that houses the “largest and most diverse botanical and mycological collections in the world” founded in the year 1840. Living collection includes more than 30,000 different kinds of plants.

While herbarium which is one of the largest in the world has over seven million preserved plant specimens. The library contains more than 7,50,000 volumes and the illustrations and also a collection of more than 1,75,000 prints, books, photographs, letters, manuscripts, periodicals, maps and botanical illustrations.

Preparation of Herbarium Specimen

International Herbarium

National Herbarium

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Botanical Gardens and its Significance

In true sense all gardens are not botanical gardens. Botanical gardens are centres for collection of plants in their various stages of living. Gardens existed for growing ornamental plants for aesthetic value, religious and status reasons. The famous “hanging gardens” of Babylon in Mesopotamia is an example. For the purpose of science and education the first garden was maintained by Theophrastus in his public lecture hall at Athens.

First modern botanical garden was established by Luca Ghini (1490-1556) a professor of Botany at Pisa, Italy in 1544. Botanical garden contains special plant collections such as cacti, succulent, green house, shade house, tropical, alpine and exotic plants. Worldwide there are about 1800 botanical gardens and arboreta.

Role of Botanical Garden:
Botanical Gardens play the following important roles.

1. Gardens with aesthetic value which attract a large number of visitors. For example, the Great Banyan Tree (Ficus benghalensis) in the Indian Botanical Garden at Kolkata.
2. Gardens have a wide range of species and supply taxonomic material for botanical research.
3. Garden is used for self-instruction or demonstration purposes.
4. It can integrate information of diverse fields like Anatomy, Embryology, Phytochemistry, Cytology, Physiology and Ecology.
5. Act as a conservation centre for diversity, rare and endangered species.
6. It offers annual list of available species and a free exchange of seeds.
7. Botanical garden gives information about method of propagation, sale of plant material to the general public.

Royal Botanic garden, Kew- England

Royal Botanic garden Kew – England is a non – departmental public body in the United Kingdom. It is the largest botanical garden in the world, established in 1760, but officially opened in the year 1841. Plant collections include Aquatic garden, Arboretum with 14,000 trees, Bonsai collection, Cacti collection and Carnivorous plant collection.

Botanical garden, also called botanic garden, originally, a collection of living plants designed chiefly to illustrate relationships within plant groups. A display garden that concentrates on woody plants (shrubs and trees) is often referred to as an arboretum.

How do I get official Botanical Garden status? The garden is open to the public on at least a part-time basis. The garden functions as an aesthetic display, educational display and/or site research. The garden maintains plant records.

Royal Botanic Gardens in Kew, England – known as the largest botanical garden in the world, this 300-acre garden near London is home to the world’s biggest collection of living plants.

Botanical gardens devote their resources to the study and conservation of plants, as well as making the world’s plant species diversity known to the public. These gardens also play a central role in meeting human needs and providing well-being.

These are specialised gargens which have collections of living plants for reference plant species in botanical gardens are grown for identification purposes and each plant is labelled by indicating its botanical name and family. e.g: 1. Kew (England).

Advantages. Botanical gardens devote their resources to the study and conservation of plants, as well as making the world’s plant species diversity known to the public. These gardens also play a central role in meeting human needs and providing well-being.

Botanical gardens make money based on their purpose. For example, a botanical garden may have a contract with a university or company to produce research on new plant species. If the space is being used largely for the public, patrons will pay an admission fee to tour the garden.

For the adjective meaning of or relating to botany or the cultivation of plants, botanic and botanical are both acceptable, and there is no difference between them. Botanical is more common, however, especially in modern.

Botanical is more common, however, especially in modern English. Firstly, botanical gardens can provide the new plants of economic importance to society, including ornamentals, medicinal, trees for reforestation, plants for industry, fruits, and cash crops. Next, some plants are collected for the study of adaptability, growth, and also the economic and genetic characteristics.

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Taxonomic Aids

Taxonomic aids are the tools for the taxonomic study. Some techniques, procedures and stored information that are useful in identification and classification of organisms are called taxonomical aids. They are required in almost all branches of biological studies for their proper identification and for finding their relationship with others. Some of the taxonomical aids are keys, flora, revisions, monograph, catalogues, herbarium, botanical gardens etc.

Keys

Taxonomic keys are the tools for the identification of unfamiliar plants. These keys are based on characters which are stable and reliable. The most common type of key is a dichotomous key. It consists of a sequence of two contrasting statements. A pair of contrasting statements is known as couplet. Each statement is known as lead. The plant is correctly identified with keys by narrowing down the characters found in plant.

Example:

1.
(a) Flowers cream-coloured; fruiting calyx enclosing the berry …… Physalis
(b) Flowers white or violet; fruiting calyx not enclosing the berry ……… 2

2.
(a) Corolla rotate; fruit a berry ….. Solanum
(b) Corolla funnel-form or salver-form; fruit a capsule: …. 3

3.
(a) Radical leaves present; flowers in racemes; fruits without prickles ….. Nicotiana
(b) Radical leaves absent; flowers solitary; fruits with prickles ….. Datura

Another type of key for identification is the Polyclave or Multi-entry key. It consists of a list of numerous character states. The user selects all states that match the specimen. Polyclave keys are implemented by a computer algorithm.

Taxonomical aids are the collections of samples or preserved organisms which help in extensive research for the identification of various taxonomic hierarchy. Taxonomic studies of various species of plants, animals, and other organisms, which require correct classifications and identification.

Taxonomical aids are the samples or collection of samples of preserved organisms that help in the research of taxonomic hierarchy. The examples are herbarium, monograph, museum, zoological parks, flora, etc. Herbarium is a store that houses plant species or specimens and other related data for study. The most important taxonomical aids are herbaria, botanical gardens, keys, museums, and zoological parks.

Manual:
These provide information for identification of names of species occurring in an area.

Monograph:
These are handbooks which provide the available information of any one taxon. Common taxonomical aids include a herbarium, botanical gardens, zoological parks, museums, keys etc.

Separate taxonomical keys are required for each taxonomic categories like Family, Genus, Species for the identification purpose. The other type of key for taxonomic studies are Flora, Manuals, Monographs and Catalogues. These help in correct identification of organism.

The taxonomic aids are the aids which help in identification, classification and naming of a newly discovered organisms (plant or animal). It could be in the form of preserved document like herbaria or specimen kept at museums or scientific institutions.

Taxonomical aids are the representations or accumulation of samples of preserved bions that help in the study of the taxonomic hierarchy. The examples are herbarium, monograph, museum, zoological parks, flora, etc.

A manual serves as a taxonomic aid by guiding individuals to accurately identify and classify different plants and animals. A manual contains basic but necessary information for categorising plants and animals. The use of a manual is usually user-defined.

A taxonomic key is a device for quickly and easily identifying to which species an unknown plant belongs. The key consists of a series of choices, based on observed features of the plant specimen.it is often referred to as a dichotomous key.

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Taxonomic Hierarchy

Taxonomic hierarchy was introduced by Carolus Linnaeus. It is the arrangement of various taxonomic levels in descending order starting from kingdom up to species. Kingdom is the highest level or rank of the classification. Example: Plantae

“Taxonomic hierarchy is the process of arranging various organisms into successive levels of the biological classification either in a decreasing or an increasing order from kingdom to species and vice versa.” Each of this level of the hierarchy is called the taxonomic category or rank.

The current taxonomic system now has eight levels in its hierarchy, from lowest to highest, they are: species, genus, family, order, class, phylum, kingdom, domain. There are seven main taxonomic ranks: kingdom, phylum or division, class, order, family, genus, species.

Taxonomy is the branch of biology that classifies all living things. He also developed a classification system called the taxonomic hierarchy, which today has eight ranks from general to specific: domain, kingdom, phylum, class, order, family, genus, and species.

Plants, Animals, Protists, Fungi, Archaebacteria, Eubacteria. How are organism placed into their kingdoms? You are probably quite familiar with the members of this kingdom as it contains all the plants that you have come to know – flowering plants, mosses, and ferns.

Phylum, Species, and Class are taxonomic category. But, Glumaceae is not a category. It is a botanical name assigned to order including the family of grass, used by Bentham and Hooker.

This phylogeny overturned the eukaryote-prokaryote dichotomy by showing that the 16S rRNA tree neatly divided into three major branches, which became known as the three domains of (cellular) life: Bacteria, Archaea and Eukarya (Woese et al 1990).

Classification, or taxonomy, is a system of categorizing living things. There are seven divisions in the system:

1. Kingdom
2. Phylum or Division
3. Class
4. Order
5. Family
6. Genus
7. Species

An example of taxonomy is the way living beings are divided up into Kingdom, Phylum, Class, Order, Family, Genus, Species. An example of taxonomy is the Dewey Decimal system – the way libraries classify non-fiction books by division and subdivisions. The science, laws, or principles of classification.

The Animal Kingdom contains more than two million known species. The Animal Kingdom contains these seven Phyla: Porifera, Cnidaria, Platyhelminthes, Annelida, Mollusca, Arthropoda, and Chordata.

Tools and taxonomical aids may be different for the study of plants and animals. The important components of the taxonomical tools are field visits, survey, identification, classification, preservation and documentation.

Thus, molecular approaches have found a niche in taxonomy. Measurement of DNA hybridization between strains is the single most definitive tool for defining a species. Data on sequences of DNA and amino acids can be used to infer phylogeny.

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International Code of Botanical Nomenclature (ICBN)

Assigning name for a plant is known as Nomenclature. This is based on the rules and recommendations of the International Code of Botanical Nomenclature. ICBN deals with the names of existing (living) and extinct (fossil) organisms. The elementary rule of naming of plants was first proposed by Linnaeus in 1751 in his Philosophia Botanica.

In 1813 a detailed set of rules regarding plant nomenclature was given by A.P. de Candolle in his famous work “Theorie elementaire de la botanique”. Then the present ICBN was evolved by following the same rules of Linnaeus, A.P. de Candolle and his son Alphonse de Candolle.

ICN Principles

International Code of Nomenclature is based on the following six principles.

1. Botanical nomenclature is independent of zoological and bacteriological nomenclature.
2. Application of names of taxonomic group is determined by means of nomenclatural types.
3. Nomenclature of a taxonomic group is based on priority of publication.
4. Each taxonomic group with a particular circumscription, position and rank can bear only one correct name.
5. Scientific names of taxonomic groups are treated as Latin regardless of their derivation.
6. The rules of nomenclature are retroactive unless expressly limited.

Codes of Nomenclature

ICN has formulated a set of rules and recommendations dealing with the botanical name of plants. International Botanical Congress is held at different places every six years. Proposals for nomenclatural changes and changes in rules are discussed and implemented. Changes are published in their website.

18^th International Botanical Congress held in 2011 at Melbourne, Australia made the following major changes.

1. The code now permits electronic publication of names of new taxa.
2. Latin diagnosis or description is not mandatory and permits the use of English or Latin for the publication of a new name (Art-39).
3. “One fungus, one name” and “one fossil one name” are important changes, the concept of anamorph and teleomorph (for fungi) and morphotaxa (for fossils) have been eliminated. (Previously, sexual and asexual stages of the fungus/fossils were provided with different names).
4. As an experiment with “registration of names” new fungal descriptions require the use of an identifier from a “recognized repository”.
5. There are two recognized repositories Index fungorum and Myco Bank.

19^th International Botanical Congress was held in Shenzhen in China in 2017. Changes accepted by International Botanical Congress are yet to be published.

Vernacular Names (Common Names)

Vernacular names are known as common names. They are very often descriptive and poetic references to plants. Common name refer to more than one plant or many plants may have same common name. These names are regional or local and are not universal. Example: Albizia amara. L belongs to Mimosaceae is called as Usilai in South Tamilnadu and Thurinji in North Tamilnadu.

Scientific Names/Botanical Names

Each and every taxon as per the ICN (species, genus, family etc) can have only one correct scientific name. Scientific name of a species is always a binomial. These names are universally applied. Example: Oryza sativa L. is the scientific name of paddy.

Polynomial

Polynomial is a descriptive phrase of a plant. Example: Ranunculus calycibus retroflexis pedunculis falcatis caule erecto folius compositis. It means butter cup with reflexed sepals, curved flower stalks, erect stem and compound leaves. Polynomial system of naming a plant is replaced by a binomial system by Linnaeus.

Binomial

Binomial nomenclature was first introduced by Gaspard Bauhin and it was implemented by Carolus Linnaeus. Scientific name of a species consists of two words and according to binomial nomenclature, the first one is called genus name and second one is specific epithet. Example: Mangifera indica. Mangifera is a genus name and indica is specific epithet. This system is in vogue even now.

Author Citation

This refers to valid name of the taxa accompanied by the author’s name who published the name validly. Example: Solanum nigrum L. There are two types of author citation.

Single Author:

When a single author proposed a valid name, the name of the author alone is accompanied by his abbreviated name. Example: Pithecellobium cinereum Benth.

Multiple Authors:

When two or more authors are associated with a valid publication of name, their names should be noted with the help of Latin word et or &. Example: Delphinium viscosum Hook. f. et Thomson. Standard Form of Author’s Abbreviations has to be followed.