plant systematics: an integrated approachpreview.kingborn.net/694000/81750f9d3cfd4a109efcd5... ·...

Plant Systematics��

Third edition

Gurcharan Singh��

��

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This third edition of integrated information on Plant Systematics has largely been influencedby the developments of the first few years of twenty first century. Past two decades haveseen development of new tools of biotechnology, vigorous utilization of molecular data inunderstanding phylogeny, and redefining affinities and arrangements of plant groups. Recentyears have also seen disappearance of gaps between numerical and cladistic methodologies,and integration of former into the latter for complete understanding of phylogeneticrelationships. These trends have largely influenced the combination of numerical andcladistic methods under one chapter, and enlarged discussion on Molecular Systematics,discussing new concepts, tools and recent achievements. New chapters on Pteridophytesand Gymnosperms have been added for complete understanding of systematics of vascularplants.

It is being increasingly realized that actual photographs of plants and plant parts enablebetter understanding of taxonomic information, the trend usefully exploited by recentpublications by Simpson (2006) and Judd et al. (3rd ed., 2008). The present editionincorporates more than 500 colour photographs of plants from diverse families of plants.High-resolution images of these as also the additional plants have been provided in theCD-ROM being supplied along with the book, latter including 772 photographs. This haslargely been possible through the kind courtesy of my son Manpreet Singh and daughter-in-law Komal, who sponsored my recent visit to California, and provided me the opportunityto visit and photograph temperate plants in and around California. The book as such containsimages of both tropical plants (largely from Delhi), temperate American plants and plantsfrom other parts of the World growing in the Botanical Gardens of University of Californiaand San Francisco Botanical Garden. I wish to record the help rendered by the members ofTAXACOM in the identification of some of the American plants.

The focus of the present edition has been to further consolidate the information on theprinciples of plant systematics, include detailed discussion on all major systems ofclassification, and significantly, also include discussion on the selected families of vascularplants, without sacrificing the discussion on basic principles. The families included fordiscussion are largely those which have wide representation, as also those that are less

Chapter 6

Preface

iv Plant Systematics

known but significant in evaluating the phylogeny of angiosperms. The discussion of thefamilies also has a considerable focus on their phylogenetic relationships, as evidenced byrecent cladistic studies, with liberal citation of molecular data. Several additional familieshave been included for detailed discussion in the present volume.

Recent internet revolution has greatly helped in propagating taxonomic information,with numerous searchable databases, online programs for identification and data analysisavailable for ready reference. The information concerning these has been included atappropriate places in various chapters for easy utilization. In light of this, the separatechapter on web has been omitted. The outputs of computer programs, especially used inmolecular studies and construction of phylogenetic trees has been included based on actualor hypothetical data. This will acquaint readers with the handling of raw data and workingof computer programs.

The author has attempted to strike a balance between classical fundamentalinformation and the recent developments in plant systematics. Special attention has beendevoted to the information on botanical nomenclature, identification and phylogeny ofangiosperms with numerous relevant examples and detailed explanation of the importantnomenclatural problems. An attempt has been made to present a continuity between orthodoxand contemporary identification methods by working on a common example. The informationon methods of identification using computers has been further enhanced to help better on-line identification.

For providing me inspiration for this book, I am indebted to my undergraduate students,who helped me to improve the material through frequent interactions. I am also indebtedto my wife Mrs. K.G. Singh for constant support and bearing with my overindulgence withthis book. I also wish to acknowledge the help rendered by my son Kanwarpreet Singh atvarious stages.

I wish to record thanks to all the colleagues whose inputs have helped me to improvethe information presented here. I also wish to place on record sincere thanks to Dr. JefVeldkamp for valuable information on nomenclature, Dr. Gertrud Dahlgren for photographsand literature, Dr. P.F. Stevens for literature on APG II and trees from his APweb, Dr.Robert Thorne for making available his 2007 classification, Dr. James Reveal for his helpon nomenclatural problems, Dr. D.L. Dilcher for his photograph, Dr. Julie Barcelona andHarry Wiriadinata for photographs of Rafflesia, the authorities of New York Botanical Garden,Missouri Botanical Garden, USA, Royal Botanic Gardens Kew and University of California,Santa Cruz, for photographs used in the book.

New Delhi Gurcharan SinghNovember 2009

Preface iii

1. PLANTS, TAXONOMY AND SYSTEMATICS 1–14Plants and Kingdoms of Life 1

Two Kingdom System 1Two Empires Three Kingdoms 2Five Kingdom System 2Six or Seven Kingdoms? 2The Plant Kingdom 6

Taxonomy and Systematics 7Basic Components (Principles) of Systematics 8Aims of Systematics 11Advancement Levels in Systematics 12

2. BOTANICAL NOMENCLATURE 15–45Need for Scientific names 15

Why Latin? 16Development of Botanical Code 16Contents of Botanical Code 17

Preamble 17Principles of ICBN 18Names of Taxa 18The Type Method 23Author Citation 25Publication of Names 26Rejection of Names 28Principle of Priority 30Names of Hybrids 34Names of Cultivated Plants 35

Chapter 6

Contents

vi Plant Systematics

Unified Biological Nomenclature 35Draft BioCode 36PhyloCode 38

3. HIERARCHICAL CLASSIFICATION 46–55Taxonomic groups, categories and ranks 46Utilization of categories 48

Species concept 49Infraspecific ranks 53Genus 54Family 54

4. DESCRIPTIVE TERMINOLOGY 56–90Habit and life span 56Habitat 57Roots 57Stems 58Leaves 61

Leaf arrangement 62Leaf duration 63Leaf incision 63Stipules 65Leaf shape 65Leaf margin 66Leaf base 66Leaf apex 67Leaf surface 68Venation 69

Inflorescence 69Racemose types 69Cymose types 70Specialized types 71

Flower 71Calyx 73Corolla 74Perianth 74Androecium 74Gynoecium 77

Fruit 79Simple fruits 80Aggregate fruits 82Multiple fruits 83

Floral formula 83Floral diagram 83

5. PROCESS OF IDENTIFICATION 91–127Specimen preparation 91

Fieldwork 91Equipment 92Collection 93Pressing 93

Handling special groups 94Drying 94

Herbarium methods 95Botanical gardens 95Herbaria 101Pest Control 105Virtual herbarium 106

Identification methods 108Taxonomic literature 108Taxonomic keys 113Cmputers in identification 120Interactive keys Id. 121

6.VARIATION, BIOSYSTEMATICS, POPULATION GENETICSAND EVOLUTION 128–148Types of variation 128

Developmental variation 129Environmental variation 129Genetic variation 129

Variance analysis 129Reproductive systems 131

Outbreeding 131Inbreeding 135Apomixis 135

Population genetics 135Allele frequencies 136Mating systems 136Hardy-Weinberg law 136

Evolution 139Mutation 140Migration 140Random genetic drift 140Natural selection 141Molecular evolution 143Neutral theory of evolution 143Speciation 144

7. TAXONOMIC EVIDENCE 149–209Morphology 149

Habit 149Underground parts 150Leaves 150Flowers 150Fruits 150

Anatomy 150Wood anatomy 150Trichomes 151Epidermal features 153Leaf anatomy 153Floral anatomy 153

Contents vii

viii Plant Systematics

Embryology 154Families marked out by distinct embryological features 154Specific examples of the role of embryological data 155

Palynology 156Pollen aggregation 156Pollen wall 157Pollen aperture 157

Micromorphology and Ultrastructure 159Micromorphology 159Ultrastructure 161

Chromosomes 164Chromosomal number 164Chromosomal structure 167Chromosomal behaviour 168

Chemotaxonomy 168Primary metabolites 169Secondary metabolites 169Non-semantide Macromolecules 178Proteins 178

Molecular systematics 184Molecular evolution 184Location of molecular data 186Molecular techniques 187DNA polymorphism 199Examples of molecular studies 204Gene trees 209

8. DEVELOPING CLASSIFICATIONS 210–264Phenetic methods 210

Principles of taxometrics 211Cladistic methods 212

Phylogenetic terms 213Phylogenetic diagrams 221Phylogeny and classification 225

Phylogenetic data analysis 229Taxa-Operational Units 229Characters 229Measure of similarity 234Construction of trees 237The Consensus tree 251Automated trees 258Gene trees and species trees 262Developing classification 263

9. PHYLOGENY OF ANGIOSPERMS 265–296Origin of Angiosperms 265

What are Angiosperms? 265What is the age of Angiosperms? 266What is the place of their origin? 268Are angiosperms monophyletic or polyphyletic? 270

What are the possible ancestors? 270Origin of monocotyledons 280

Basal living angiosperms 280Casuarinaceae 281Magnoliids 281Paleoherbs 282

Evolutionary trends 285Coevolution with animals 285Basic evolutionary trends 286Xylem evolution 287Stamen evolution 289Pollen grain evolution 292Carpel evolution 292Evolution of inferior ovary 296

10. SYSTEMS OF CLASSIFICATION 297–358Classifications based on gross morphology 297

Preliterate mankind 297Early literate civilisations 297Medieval Botany 299Renaissance 300

Sexual System 302Carolus Linnaeus 303

Natural Systems 306Michel Adanson 306Jean B. P. Lamarck 306de Jussieu family 306de Candolle family 307Robert Brown 308George Bentham and Sir J. D. Hooker 308

Phylogenetic Systems 312Transitional Systems 312Intentional phylogenetic systems 316Modern phylogenetic systems 324

11. FAMILIES OF PTERIDOPHYTES 359–383Lycopodiophtes

Lycopodiaceae 362Selaginellaceae 363Isoetaceae 365

PsilopsidaOphioglossaceae 366Psilotaceae 368

EquisetopsidaEquisetaceae 370

PteropsidaOsmundaceae 371Marsileaceae 373Salviniaceae 374Cyatheaceae 376Pteridaceae 377

Contents ix

x Plant Systematics

Aspleniaceae 379Dryopteridaceae 380Polypodiaceae 382

12. FAMILIES OF GYMNOSPERMS 384–406Cycadales

Cycadaceae 386Zamiaceae 387

GinkgoalesGinkgoaceae 389

ConiferalesPinaceae 391Cupressaceae 393Podocarpaceae 395Araucariaceae 396Taxaceae 398

GnetalesEphedraceae 399Gnetaceae 401

13. MAJOR FAMILIES OF ANGIOSPERMS 407–678Angiosperms roll of honour 408Chloranthidae 409

Amborellaceae 409Chloranthaceae 411Austrobaileyaceae 413WinteraceaeIlliciaceae 415Cabombaceae 417Nymphaeaceae 419Ceratophyllaceae 421

Magnoliidae 423Magnoliaceae 423Degeneriaceae 425Annonaceae 427Calycanthaceae 429Lauraceae 431Winteraceae 433Saururaceae 435Piperaceae 437

Alismatidae 439Acoraceae 439Araceae 441Butomaceae 443Alismataceae 445Hydrocharitaceae 447Potamogetonaceae 449

Liliidae 451Pandanaceae 451Dioscoreaceae 453Smilacaceae 455

Liliaceae 473Orchidaceae 475Iridaceae 478Asphodelaceae 480Alliaceae 482Subfamily 484Agavaceae 485

Commelinidae 487Arecaceae 488Commelinaceae 490Musaceae 492Zingiberaceae 494Cannaceae 496Juncaceae 498Cyperaceae 500Poaceae 502

Ranunculidae 505Paeoniaceae 505Berberidaceae 507Ranunculaceae 509Papaveraceae 512

Hamamelididae 514Saxifragaceae 514Fagaceae 517Betulaceae 519Casuarinaceae 521

Caryophyllidae 523Portulacaceae 524Cactaceae 526Nyctaginaceae 528Aizoaceae 530Chenopodiaceae 532Amaranthaceae 534Caryophyllaceae 536Polygonaceae 538Droseraceae 540

Rosidae 542Celastraceae 543Violaceae 545Salicaceae 547Cucurbitaceae 550Clusiaceae 552Euphorbiaceae 554Oxalidaceae 557Zygophyllaceae 559Geraniaceae 561Rosaceae 563Fabaceae 566Myrtaceae 572

Contents xi

xii Plant Systematics

Lythraceae 574Onagraceae 577

Malvidae 579Malvaceae 580Grewiaceae 583Dipterocarpaceae 584Rhamnaceae 586Ulmaceae 588Moraceae 590Urticaceae 592Rafflesiaceae 595Capparaceae 597Cleomaceae 599Brassicaceae 600Rutaceae 603Meliaceae 605Anacardiaceae 607Sapindaceae 610

Asteridae 612Hydrangeaceae 613Cornaceae 627Balsaminaceae 629Polemoniaceae 631Ebenaceae 633Sapotaceae 635Primulaceae 637Ericaceae 639Adoxaceae 642Apiaceae 644Araliaceae 646Asteraceae 649

Lamiidae 652Solanaceae 652Convolvulaceae 655Boraginaceae 657Rubiaceae 659Apocynaceae 661Plantaginaceae 664Lamiaceae 666Verbenaceae 669Bignoniaceae 671Acanthaceae 673Scrophulariaceae 675

REFERENCES 669–702

INDEX 703–742

The page numbers referred below are those of the text pages where the B/Wimages of the figures appear.

Stems 85Leaves 86Inflorescences 87Fruits 88Pteridophytes 403

Selaginellaceae, Osmundaceae, Blechnaceae 403Gymnosperms

Cycadaceae, Zamiaceae 404Ginkgoaceae, Pinaceae, Cupressaceae 405

Angiosperms 457Chloranthidae 457Magnoliidae 458Araceae, Alismataceae, Hydrocharitaceae, Liliaceae 459Iridaceae, Asphodelaceae, Alliaceae 460Hyacinthaceae, Agavaceae, Asparagaceae, Nolinaceae 461Arecaceae, Musaceae, Commelinaceae, Cyperceae, Poaceae 462Paeoniaceae, Berberidaceae, Papaveraceae 463Ranunculaceae 464Grossulariaceae, Fagaceae, Nothofagaceae, Betulaceae 465Portulacaceae, Cactaceae, Nyctaginaceae, Aizoaceae 466Chenpodiaceae, Amaranthaceae, Caryophyllaceae, Polygonaceae 467Celastraceae, Violaceae, Cucurbitaceae, Begoniaceae 468Clusiaceae, Euphorbiaceae, Oxalidaceae 469Geraniaceae, Rosaceae 470Fabaceae 471Myrtaceae, Lythraceae, Onagraceae 472Malvaceae, Rhamnaceae, Moraceae 615Rafflesiaceae, Brassicaceae 616Rutaceae, Anacardiaceae, Meliaceae 617Sapindaceae 618Hydrangeaceae, Polemoniaceae, Cornaceae, Primulaceae 619Ericaceae, Adoxaceae 620Apiaceae, Araliaceae 621Asteraceae 622Solanaceae, Convolvulaceae, Boraginaceae 623Rubiaceae, Apocynaceae 624Plantaginaceae, Lamiaceae 625Verbenaceae, Bignoniaceae, Acanthaceae, Scrophulariaceae 626

Contents xiii

Color Plate Section

Taxonomy (or systematics) is basically con-cerned with the classification of organisms.Living organisms are placed in groups on thebasis of similarities and differences at theorganismic, cellular, and molecular levels.The United Nations EnvironmentProgramme’s Global Biodiversity Assessmentestimates the number of described speciesof living organisms as approximately 1.75million. The list grows longer every year. Clas-sifying these organisms has been a majorchallenge, and the last few decades have seena lot of realignments as additional ultrastruc-tural and molecular information piles up.These realignments have primarily been theresult of realization that the branches of thephylogenetic tree must be based on the con-cept of monophyly, and each taxonomicgroup, kingdoms included, should be mono-phyletic.

Before attempting to classify the variousorganisms, it is necessary to identify andname them. A particular group of individu-als, unique in several respects, is given aunique binomial, and is recognized as a spe-cies. These species are grouped into taxo-nomic groups, which are successively as-signed the ranks of genera, families, orders,and the process continues till all the spe-cies have been arranged (classified) under

a single largest, most inclusive group. Clas-sifying organisms and diverse forms of lifeis challenging task before the biologists.

PLANTS AND KINGDOMS OF LIFEPlants are man’s prime companions in thisuniverse, being the source of food and en-ergy, shelter and clothing, drugs and bever-ages, oxygen and aesthetic environment, andas such they have been the dominant com-ponent of his taxonomic activity through theages. Before attempting to explore the diver-sity of plant life it is essential to understandas to what is our understanding of the termPlant, and the position of plants in the webof life. Traditionally the plants are delimitedas organisms possessing cell wall, capableof photosynthesis, producing spores andhaving sedentary life. A lot of rethinking hasresulted in several different interpretationsof the term plant.

Two Kingdom SystemThe living organisms were originally groupedinto two kingdoms. Aristotle divided all liv-ing things between plants, which generallydo not move or have sensory organs, andanimals. Linnaeus in his Systema naturae

Chapter 1

Plants, Taxonomy and Systematics

2 Plant Systematics

published in 1735 placed them underAnimalia (Animals) and Vegetabilia (Plants)as two distinct kingdoms (Linnaeus placedminerals in the third kingdom Mineralia).Linnaeus divided each kingdom into classes,later grouped into phyla for animals and di-visions for plants. When single-celled organ-isms were first discovered, they were splitbetween the two kingdoms: mobile forms inthe animal phylum Protozoa, and coloredalgae and bacteria in the plant division Thal-lophyta or Protophyta. As a result, ErnstHaeckel (1866) suggested creating a thirdkingdom Protista for them, although thiswas not very popular until relatively recently(sometimes also known as Protoctista).Haeckel recognized three kingdoms: Pro-tista, Plantae and Animalia.

Two Empires Three KingdomsThe subsequent discovery that bacteria areradically different from other organisms inlacking a nucleus, led Chatton (1937) to pro-pose a division of life into two empires: or-ganisms with a nucleus in Eukaryota andorganisms without in Prokaryota. Prokary-otes do not have a nucleus, mitochondria orany other membrane bound organelles. Inother words neither their DNA nor any otherof their metabolic functions are collected to-gether in a discrete membrane enclosed area.Instead everything is openly accessible withinthe cell, though some bacteria have internalmembranes as sites of metabolic activitythese membranes do not enclose a separatearea of the cytoplasm. Eukaryotes have aseparate membrane bound nucleus, numer-ous mitochondria and other organelles suchas the Golgi Body within each of their cells.These areas are separated off from the mainmass of the cell’s cytoplasm by their ownmembrane in order to allow them to be morespecialized. The nucleus contains all theEukaryote cell DNA, which gets organizedinto distinct chromosomes during the pro-cess of mitosis and meiosis. The energy isgenerated in mitochondria. The exception tothis rule are red blood cells which have nonucleus and do not live very long. Chatton’s

proposal, however, was not taken up imme-diately, because another classification wasproposed by Herbert Copeland (1938), whogave the prokaryotes a separate kingdom,originally called Mycota but later referred toas Monera or Bacteria. Copeland later on(1956) proposed a four-kingdom systemplacing all eukaryotes other than animalsand plants in the kingdom Protoctista, thusrecognizing four kingdoms Monera,Protoctista, Plantae and Animalia. The im-portance of grouping these kingdoms in twoempires, as suggested earlier by Chattonwas popularized by Stanier and van Niel(1962), and soon became widely accepted.

Five Kingdom SystemAmerican biologist Robert H. Whittaker(1969) proposed the removal of fungi into aseparate kingdom thus establishing a fivekingdom system recognizing Monera, Pro-tista, Fungi, Plantae and Animalia as dis-tinct kingdoms. The fungi like plants havea distinct cell wall but like animals lackautotrophic mode of nutrition. They, how-ever, unlike animals draw nutrition fromdecomposition of organic matter, have cellwall reinforced with chitin, cell membranescontaining ergosterol instead of cholesteroland have a unique biosynthetic pathway forlysine. The classification was followed widelyin textbooks.

Six or Seven Kingdoms?Subsequent research concerning the organ-isms previously known as archebacteria hasled to the recognition that these creaturesform an entirely distinct kingdom Archaea.These include anaerobic bacteria found inharsh oxygen-free conditions and are geneti-cally and metabolically completely differentfrom other, oxygen-breathing organisms. These bacteria, called Archaebacteria, orsimply Archaea, are said to be “living fossils”that have survived since the planet’s veryearly ages, before the Earth’s atmosphereeven had free oxygen. This together with theemphasis on phylogeny requiring groups to

Plants, Taxonomy and Systematics 3

be monophyletic resulted in a six kingdomsystem proposed by Carl Woese et al. (1977).They grouped Archaebacteria and Eubacteriaunder Prokaryotes and rest of the four king-doms Protista, Fungi, Plantae and Animaliaunder Eukaryotes. They subsequently (1990)grouped these kingdoms into three domainsBacteria (containing Eubacteria), Archaea(containing Archaebacteria) and Eukarya(containing Protista, Fungi, Plantae andAnimalia).

Margulis and Schwartz (1998) proposedterm superkingdom for domains and recog-nized two superkingdoms: Prokarya(Prokaryotae) and Eukarya (Eukaryotae).Former included single kingdom Bacteria(Monera) divided into two subkingdomsArchaea and Eubacteria. Eukarya wasdivided into four kingdoms: Protoctista (Pro-tista), Animalia, Plantae and Fungi.

Several recent authors have attempted torecognize seventh kingdom of living organ-

isms, but they differ in their treatment. Ross(2002, 2005) recognized Archaebacteria andEubacteria as separate kingdoms, named asProtomonera and Monera, respectively againunder separate superkingdoms (domains ofearlier authors) Archaebacteriae andEubacteria. He added seventh kingdomMyxomycophyta of slime moulds undersuperkingdom Eukaryotes. Two additionalsuperkingdoms of extinct organisms Pro-genotes (first cells) and Urkaryotes (prokary-otic cells that became eukaryotes) were added:

Superkingdom Progenotes.... ....first cells now extinct

Superkingdom ArchaebacteriaeKingdom Protomonera...archaic bacteria

Superkingdom EubacteriaKingdom Monera........bacteria

Superkingdom Urkaryotes...prokaryoti cells that became eukaryotes

Figure 1.1 Seven kingdoms of life and their possible phylogeny (after Patterson & Sogin 1992).

4 Plant Systematics

Superkingdom Eukaryotes...cells with nuclei

Kingdom Protista..........protozoansKingdom Myxomycophyta...slime moldsKingdom Plantae............plantsKingdom Fungi..............fungiKingdom Animalia...........animals

Patterson & Sogin (1992; Figure 1.1) rec-ognized seven kingdoms, but included slimemoulds under Protozoa (Protista) and insteadestablished Chromista (diatoms) as seventhkingdom. Interestingly the traditional algaenow find themselves distributed in three dif-ferent kingdoms: eubacterial prokaryotes(the blue-green cyanobacteria), chromistans(diatoms, kelps), and protozoans (green al-gae, red algae, dinoflagellates, euglenids).

Cavalier-Smith (1981) suggested that Eu-karyotes can be classified into nine kingdomseach defined in terms of a unique constella-tion of cell structures. Five kingdoms haveplate-like mitochondrial cristae: (1) Eufungi(the non-ciliated fungi, which unlike theother eight kingdoms have unstacked Golgicisternae), (2) Ciliofungi (the posteriorly cili-ated fungi), (3) Animalia (Animals, sponges,mesozoa, and choanociliates; phagotrophswith basically posterior ciliation), (4)Biliphyta (Non-phagotrophic, phycobilisome-containing, algae; i.e. the Glaucophyceae andRhodophyceae), (5) Viridiplantae (Non-phagotrophic green plants, with starch-con-taining plastids). Kingdom (6), theEuglenozoa, has disc-shaped cristae and anintraciliary dense rod and may bephagotrophic and/or phototrophic with plas-tids with three-membraned envelopes. King-dom (7), the Cryptophyta, has flattened tu-bular cristae, tubular mastigonemes on bothcilia, and starch in the compartment betweenthe plastid endoplasmic reticulum and theplastid envelope; their plastids, if present,have phycobilins inside the paired thylakoidsand chlorophyll c2. Kingdom (8), theChromophyta, has tubular cristae, togetherwith tubular mastigonemes on one anteriorcilium and/or a plastid endoplasmic reticu-lum and chlorophyll c1 + c2. Members of the

ninth kingdom, the Protozoa, are mainlyphagotrophic, and have tubular or vesicularcristae (or lack mitochondria altogether), andlack tubular mastigonemes on their (primi-tively anterior) cilia; plastids if present havethree-envelop membranes, chlorophyll c2,and no internal starch, and a plastid endo-plasmic reticulum is absent. Kingdoms 4-9are primitively anteriorly biciliate. A simplersystem of five kingdoms suitable for very el-ementary teaching is possible by grouping thephotosynthetic and fungal kingdoms in pairs.It was suggested that Various compromisesare possible between the nine and five king-doms systems; it is suggested that the bestone for general scientific use is a system ofseven kingdoms in which the Eufungi andCiliofungi become subkingdoms of the King-dom Fungi, and the Cryptophyta andChromophyta subkingdoms of the KingdomChromista; the Fungi, Viridiplantae,Biliphyta, and Chromista can be subject tothe Botanical Code of Nomenclature, whilethe Zoological Code can govern the KingdomsAnimalia, Protozoa and Euglenozoa.

These 9 kingdoms together with two orone kingdom of prokaryotes total eleven orten kingdoms of life. Subsequently, however,Cavalier-Smith (1998, 2000, 2004) revertedback to six kingdom classification recogniz-ing Bacteria, Protozoa, Animalia, Fungi,Plantae and Chromista under two empiresProkaryota and Eukaryota. Prokaryotes con-stitute a single kingdom, Bacteria, here di-vided into two new subkingdoms:Negibacteria, with a cell envelope of two dis-tinct genetic membranes, and Unibacteria,comprising the phyla Archaebacteria andPosibacteria. Outline of the classification isas under:

Empire ProkaryotaKingdom Bacteria

Subkingdom Negibacteria (phyla Eobacteria, Sphingobacteria, Spirochaetae, Proteobacteria, Planctobacteria, Cyanobacteria)Subkingdom Unibacteria (phyla Posibacteria, Archaebacteria)


Empire EukaryotaKingdom Protozoa

Subkingdom Sarcomastigota (phylaAmoebozoa, Choanozoa)

Subkingdom BiciliataKingdom Animalia (Myxozoa and 21other phyla)

Kingdom Fungi (phyla Archemycota,Microsporidia, Ascomycota,Basidiomycota)

Kingdom PlantaeSubkingdom Biliphyta (phylaGlaucophyta, Rhodophyta)

Subkingdom Viridaeplantae (phylaChlorophyta, Bryophyta,Tracheophyta)

Kingdom ChromistaSubkingdom Cryptista (phylumCryptista: cryptophytes, goniomonads,katablepharids)

Subkingdom Chromobiota

The name archaebacteria seems to be con-fusing. They were so named because theywere thought to be the most ancient (Greek‘archaio’ meaning ancient) and sometimeslabelled as living fossils, since they can sur-vive in anaerobic conditions (methanogens-which use hydrogen gas to reduce carbon di-oxide to methane gas), high temperatures(thermophiles, which can survive in tem-peratures of up to 80 degree C), or salty places(halophiles). They differ from bacteria in hav-ing methionine as aminoacid that initiatesprotein synthesis as against formyl-methion-ine in bacteria, presence of introns in somegenes, having several different RNA poly-merases as against one in bacteria, absenceof peptidoglycan in cell wall, and growth notinhibited by antibiotics like streptomycin andchloramphenicol. In several of these respectsarchaebacteria are more similar to eukary-otes. Bacteria are thought to have divergedearly from the evolutionary line (the cladeneomura, with many common characters,notably obligately co-translational secretionof N-linked glycoproteins, signal recognitionparticle with 7S RNA and translation-arrestdomain, protein-spliced tRNA introns, eight-

subunit chaperonin, prefoldin, core histones,small nucleolar ribonucleoproteins (snoRNPs),exosomes and similar replication, repair,transcription and translation machinery)that gave rise to archaebacteria and eukary-otes. It is, as such more appropriate to callarchaebacteria as metabacteria. The eukaryotic host cell evolved from some-thing intermediate between posibacteria andmetabacteria (“archaebacteria”), which hadevolved many metabacterial features but notyet switched to ether-linked lipid membranesin a major way. They would no doubt cladis-tically fall out as primitive metabacteria, butwhether such forms are still extant is un-certain. There are lots of metabacteria outthere which are uncultured (only known fromenvironmental sequences) or just undiscov-ered, so who knows.

The further shift from archaebacteria toEukaryotes involved the transformation ofcircular DNA into a linear DNA bound withhistones, formation of membrane boundnucleus enclosing chromosomes, develop-ment of mitosis, occurrence of meiosis insexually reproducing organisms, appearanceof membrane bound organelles such as en-doplasmic reticulum, golgi bodies and ly-sosomes, appearance of cytoskeletal ele-ments like actin, myosin and tubulin, andthe formation of mitochondria through en-dosymbiosis.

A major shift in this eukaryotic linewhich excluded animal and fungi, involvedthe development of chloroplast by an eu-karyotic cell engulfing a photosynthetic bac-terial cell (probably a cyanobacterium). Thebacterial cell continued to live and multiplyinside the eukaryotic cell, provided highenergy products, and in turn received a suit-able environment to live in. The two thusshared endosymbiosis. Over a period of timethe bacterial cell lost ability to live indepen-dently, some of the bacterial genes gettingtransferred to eukaryotic host cell, makingthe two biochemically interdependent. Chlo-roplast evolution in Euglenoids and Di-noflagellates occurred through secondaryendosymbiosis, wherein eukaryotic cell

6 Plant Systematics

engulfed an eukaryotic cell containing achloroplast. This common evolutionary se-quence is shared by green plants (includ-ing green algae; green chloroplast), red al-gae (red chloroplast) and brown algae andtheir relatives (commonly known asstramenopiles; brown chloroplast), in whichdiversification of chloroplast pigments oc-

curred, along with the thylakoid structureand a variety of storage products

The Plant KingdomIt is now universally agreed that membersof the plant kingdom include, without doubtthe green algae, liverworts and mosses, pteri-

Linear DNA, with histonesMembrane bound nucleus

Mitosis , Meiosis

ER, Golgi, lysosomesCytoskeletal elements: actin, myosin, tubulin

Mitochondria

Chloroplast(primary endosymbiosis)

Green chloroplast

Anim

alia

Fungi

Angiosperm

s

Gym

nosperms

Bryophytes

Pteridophytes

Green algae

Red algae

Brow

n algae

Glaucophytes

Dinoflagellates

Euglenoides

Archaebacteria

Bacteria

CuticleGametangia

Embryo

Sporophyte independent

Vascular tissue

Secondary growthSeeds

Carpel, stamen

Chloroplast(secondaryEndosymbiosis)

Chloroplast(secondaryEndosymbiosis)

Figure 1.2 Cladogram showing the evolution of major groups of organisms and the associatedapomorphies. Chloroplast evolution has occurred twice, once (primary endosymbiosis)eukaryote cell engulfing a photosynthetic bacterial cell, and elewhere (secondaryendosymbiosis) eukaryotic cell engulfing an eukaryotic cell containing chloroplast.


dophytes, gymnosperms and finally the an-giosperms, the largest group of plants. Allthese plants share a green chloroplast. Redalgae, Brown algae and Glaucophytes, lattertwo together known as stramenophiles, alsobelong to this kingdom. All these groupsshare the presence of a chloroplast. All greenplants share a green chloroplast with chlo-rophyll b, chlorophyll a, thylakoids andgrana, and starch as storage food. Evolutionof cuticle combined with gametangia andembryo characterizes embryophytes, includ-ing bryophytes, pteridophytes and seedplants. The development of vascular tissueof phloem and xylem, and independent sporo-phyte characterize tracheophytes includingpteridophytes and seed plants. Secondarygrowth resulting in the formation of woodand seed habit differentiates seed plants. Thefinal evolution of a distinct flower, carpelsand stamens, together with vessels and sievetubes set apart the angiosperms, the mosthighly evolved group of plants.

The species of living organisms on thisplanet include Monera-10,000; Protista-250,000; Fungi-100,000; Plantae-279,000;Animalia-1,130,000. Nearly three fourth ofanimals are insects (800,0000) and of thesemore than one third beetles (300,000).Amongst plants nearly 15,000 species be-long to usually overlooked mosses and liv-erworts, 10,000 ferns and their allies, 820to gymnosperms and 253,000 to an-giosperms (belonging to about 485 familiesand 13,372 genera), considered to be themost recent and vigorous group of plantsthat have occurred on earth. Angiospermsoccupy the majority of the terrestrial spaceon earth, and are the major components ofthe world’s vegetation.

Brazil and Colombia, both located in thetropics, are considered to be countries withthe most diverse angiosperms floras andwhich rank first and second. China, eventhough the main part of her land is not lo-cated in the tropics, the number of her an-giosperms still occupies the third place inthe world, and has approximately 300 fami-lies, 3, 100 genera and 30,000 species.

TAXONOMY AND SYSTEMATICS

There are slightly more than one third of amillion species of plants known to man to-day, the information having been accumu-lated through efforts of several millenniums.Although man has been classifying plantssince the advent of civilization, taxonomywas recognized as a formal subject only in1813 by A. P. de Candolle as a combinationof Greek words taxis (arrangement) and no-mos (rules or laws) in his famous workTheorie elementaire de la botanique. For along time plant taxonomy was considered as‘the science of identifying, naming, and clas-sifying plants’ (Lawrence, 1951). Since iden-tification and nomenclature are importantprerequisites for any classification, taxonomyis often defined as the ‘science dealing withthe study of classification, including itsbases, principles, rules and procedures’(Davis and Heywood, 1963).

Although Systematics was recognized asa formal major field of study only during thelatter half of twentieth century, the termhad been in use for a considerable period.Derived from the Latin word systema (orga-nized whole), forming the title of the famouswork of Linnaeus Systema naturae (1735), theterm Systematics first appeared in his Gen-era Plantarum (1737), though Huxley (1888)is often credited to have made the first useof the term in his article in Nature on thesystematics of birds. Simpson (1961) definedsystematics as a ‘scientific study of thekinds and diversity of organisms, and ofany and all relationships between them’.It was recognized as a more inclusive fieldof study concerned with the study of diver-sity of plants and their naming, classifica-tion and evolution. The scope of taxonomyhas, however, been enlarged in recent yearsto make taxonomy and systematics synony-mous. A broader definition (Stace, 1980) oftaxonomy, to coincide with systematics rec-ognized it as ‘the study and description ofvariation in organisms, the investigationof causes and consequences of this varia-tion, and the manipulation of the data

8 Plant Systematics

obtained to produce a system of classifi-cation’.

Realization of the fact that a good numberof authors still consider taxonomy to be amore restricted term and systematics a moreinclusive one has led recent authors to pre-fer the term systematics to include discus-sion about all recent developments in theirworks. Modern approach to systematics aimsat reconstructing the entire chronicle ofevolutionary events, including the formationof separate lineages and evolutionary modi-fications in characteristics of the organisms.It ultimately aims at discovering all thebranches of the evolutionary tree of life; andto document all the changes and to describeall the species which form the tips of thesebranches. This won’t be possible unless in-formation is consolidated in the form of anunambiguous system of classification. This,however, is again impossible without a clearunderstanding of the basic identification andnomenclatural methods. Equally importantis the understanding of the recent tools ofdata handling, newer concepts ofphylogenetics, expertise in the judicious uti-lization of fast accumulating molecular datain understanding of affinities between taxa.

Prior to the evolutionary theory of Darwin,relationships were expressed as natural af-finities on the basis of an overall similarityin morphological features. Darwin usheredin an era of assessing phylogenetic rela-tionships based on the course of evolution-ary descent. With the introduction of com-puters and refined statistical procedures,overall similarity is represented as pheneticrelationship, which takes into account ev-ery available feature, derived from such di-verse fields as anatomy, embryology, mor-phology, palynology, cytology, phytochemis-try, physiology, ecology, phytogeography andultrastructure.

With the advancement of biological fields,new information flows continuously and thetaxonomists are faced with the challenge ofintegrating and providing a synthesis of allthe available data. Systematics now is, thus,an unending synthesis, a dynamic science

with never-ending duties. The continuousflow of data necessitates rendering descrip-tive information, revising schemes of iden-tification, revaluating and improving sys-tems of classification and perceiving newrelationships for a better understanding ofthe plants. The discipline as such includesall activities that are a part of the effort toorganize and record the diversity of plantsand appreciate the fascinating differencesamong the species of plants. Systematic ac-tivities are basic to all other biological sci-ences, but also depend, in turn, on other dis-ciplines for data and information useful inconstructing classification. Certain disci-plines of biology such as cytology, genetics,ecology, palynology, paleobotany and phyto-geography are so closely tied up with sys-tematics that they can not be practiced with-out basic systematic information. Experi-ments cannot be carried out unless the or-ganisms are correctly identified and someinformation regarding their relationship isavailable. The understanding of relation-ships is particularly useful in the appliedfields of plant breeding, horticulture, forestryand pharmacology for exploring the useful-ness of related species. Knowledge of sys-tematics often guides the search for plantsof potential commercial importance.

Basic Components (Principles)of SystematicsVarious systematic activities are directedtowards the singular goal of constructing anideal system of classification that necessi-tates the procedures of identification, de-scription, nomenclature and constructing af-finities. This enables a better managementof information to be utilized by differentworkers, investigating different aspects,structure and functioning of different spe-cies of plant.

IdentificationIdentification or determination is recognizingan unknown specimen with an already


known taxon, and assigning a correct rankand position in an extant classification. Inpractice, it involves finding a name for anunknown specimen. This may be achieved byvisiting a herbarium and comparing unknownspecimen with duly identified specimensstored in the herbarium. Alternately, thespecimen may also be sent to an expert inthe field who can help in the identification.

Identification can also be achieved usingvarious types of literature such as Floras,Monographs or Manuals and making use ofidentification keys provided in these sourcesof literature. After the unknown specimenhas been provisionally identified with thehelp of a key, the identification can be fur-ther confirmed by comparison with the de-tailed description of the taxon provided in theliterature source.

A method that is becoming popular overthe recent years involves taking a photo-graph of the plant and its parts, uploadingthis picture on the website and informingthe members of appropriate electronic Listsor Newsgroups, who can see the photographat the website and send their comments tothe enquirer. Members of the fraternity couldthus help each other in identification in amuch efficient manner.

DescriptionThe description of a taxon involves listingits features by recording the appropriatecharacter states. A shortened descriptionconsisting of only those taxonomic charac-ters which help in separating a taxon fromother closely related taxa, forms the diag-nosis, and the characters are termed as di-agnostic characters. The diagnostic char-acters for a taxon determine its circumscrip-tion. The description is recorded in a set pat-tern (habit, stem, leaves, flower, sepals, pet-als, stamens, carpels, fruit, etc.). For eachcharacter, an appropriate character-state islisted. Flower colour (character) may thus bered, yellow, white, etc. (states). The descrip-tion is recorded in semi-technical languageusing specific terms for each character stateto enable a proper documentation of data.

Whereas the fresh specimens can be de-scribed conveniently, the dry specimens needto be softened in boiling water or in a wet-ting agent before these could be described.Softening is often essential for dissection offlowers in order to study their details.

NomenclatureNomenclature deals with the determinationof a correct name for a taxon. There aredifferent sets of rules for different groups ofliving organisms. Nomenclature of plants(including fungi) is governed by the Inter-national Code of Botanical Nomenclature(ICBN) through its rules and recommenda-tions. Updated every six years or so, theBotanical Code helps in picking up a singlecorrect name out of numerous scientificnames available for a taxon, with a particu-lar circumscription, position and rank. Toavoid inconvenient name changes for cer-tain taxa, a list of conserved names isprovided in the Code. Cultivated plants aregoverned by the International Code of No-menclature for Cultivated Plants (ICNCP),slightly modified from and largely based onthe Botanical Code.

Names of animals are governed by the In-ternational Code of Zoological Nomenclature(ICZN); those of bacteria by InternationalCode for the Nomenclature of Bacteria(ICNB), now called Bacteriological Code (BC).A separate Code exists for viruses, namedthe International Code of Virus Classifica-tion and Nomenclature (ICVCN).

With the onset of electronic revolution andthe need to have a common database for liv-ing organisms for global communication acommon uniform code is being attempted.The Draft BioCode is the first public expres-sion of these objectives. The first draft wasprepared in 1995. After successive reviewsthe fourth draft, named Draft BioCode (1997)prepared by the International Committee forBionomenclature was published by Greuteret al., (1998) and is now available on the web.The last decade of twentieth century also sawthe development of rankless PhyloCodebased on the concepts of phylogenetic

10 Plant Systematics

systematics. It omits all ranks except spe-cies and ‘clades’ based on the concept of rec-ognition of monophyletic groups. The latestversion of PhyloCode (PhyloCode4b, 2007) isalso available on the web.

PhylogenyPhylogeny is the study of the genealogy andevolutionary history of a taxonomic group.Genealogy is the study of ancestral relation-ships and lineages. Relationships are de-picted through a diagram better known as aphylogram (Stace, 1989), since the com-monly used term cladogram is more appro-priately used for a diagram constructedthrough cladistic methodology. A phylogramis a branching diagram based on the degreeof advancement (apomorphy) in the descen-dants, the longest branch representing themost advanced group. This is distinct from aphylogenetic tree in which the vertical scalerepresents a geological time-scale and all liv-ing groups reach the top, with primitive onesnear the centre and advanced ones near theperiphery. Monophyletic groups, including allthe descendants of a common ancestor, arerecognized and form entities in a classifica-tion system. Paraphyletic groups, whereinsome descendants of a common ancestor areleft out, are reunited. Polyphyletic groups, withmore than one common ancestor, are splitto form monophyletic groups. Phenetic infor-mation may often help in determining a phy-logenetic relationship.

ClassificationClassification is an arrangement of organ-isms into groups on the basis of similari-ties. The groups are, in turn, assembled intomore inclusive groups, until all the organ-isms have been assembled into a singlemost inclusive group. In sequence of in-creasing inclusiveness, the groups are as-signed to a fixed hierarchy of categoriessuch as species, genus, family, order, classand division, the final arrangement consti-tuting a system of classification. The pro-cess of classification includes assigning ap-propriate position and rank to a new taxon

(a taxonomic group assigned to any rank; pl.taxa), dividing a taxon into smaller units,uniting two or more taxa into one, transfer-ring its position from one group to anotherand altering its rank. Once established, aclassification provides an important mecha-nism of information storage, retrieval andusage. This ranked system of classificationis popularly known as the Linnaean sys-tem. Taxonomic entities are classified indifferent fashions:

1. Artificial classification is utilitarian,based on arbitrary, easily observablecharacters such as habit, colour, num-ber, form or similar features. Thesexual system of Linnaeus, which fitsin this category, utilized the numberof stamens for primary classificationof the flowering plants.

2. Natural classification uses overallsimilarity in grouping taxa, a conceptinitiated by M. Adanson and culminat-ing in the extensively used classifi-cation of Bentham and Hooker. Natu-ral systems of the eighteenth andnineteenth centuries used morphol-ogy in delimiting the overall similar-ity. The concept of overall similarityhas undergone considerable refine-ment in recent years. As against thesole morphological features as indica-tors of similarity in natural systems,overall similarity is now judged on thebasis of features derived from all theavailable fields of taxonomic informa-tion (phenetic relationship).

3. Phenetic Classification makes theuse of overall similarity in terms of aphenetic relationship based on datafrom all available sources such as mor-phology, anatomy, embryology, phy-tochemistry, ultrastructure and, infact, all other fields of study. Pheneticclassifications were strongly advo-cated by Sneath and Sokal (1973) butdid not find much favour with majorsystems of classification of higherplants. Phenetic relationship has,however, been very prominently used


in modern phylogenetic systems todecide the realignments within thesystem of classification.

4. Phylogenetic classification is basedon the evolutionary descent of a groupof organisms, the relationship de-picted either through a phylogram,phylogenetic tree or a cladogram.Classification is constructed with thispremise in mind, that all the descen-dants of a common ancestor should beplaced in the same group (i.e., groupshould be monophyletic). If some de-scendents have been left out, render-ing the group paraphyletic, these arebrought back into the group to makeit monophyletic (merger ofAsclepiadaceae with Apocynaceae,and the merger of Capparaceae withBrassicaceae in recent classifica-tions). Similarly, if the group is poly-phyletic (with members from morethan one phyletic lines, it is split tocreate monophyletic taxa (GenusArenaria split into Arenaria andMinuartia). This approach, known ascladistics, is practiced by cladists.

5. Evolutionary taxonomic classifica-tion differs from a phylogenetic clas-sification in that the gaps in the varia-tion pattern of phylogenetically adja-cent groups are regarded as more im-portant in recognizing groups. It ac-cepts leaving out certain descendantsof a common ancestor (i.e. recogniz-ing paraphyletic groups) if the gapsare not significant, thus failing to pro-vide a true picture of the genealogicalhistory. The characters considered tobe of significance in the evolution (andthe classification based on these) aredependent on expertise, authority andintuition of systematists. Such clas-sifications have been advocated bySimpson (1961), Ashlock (1979), Mayrand Ashlock (1991) and Stuessy (1990).The approach, known as eclecticism,is practiced by eclecticists.

The contemporary phylogenetic systems ofclassification, including those of Takhtajan,

Cronquist, Thorne and Dahlgren, are largelybased on decisions in which phenetic infor-mation is liberally used in deciding the phy-logenetic relationship between groups, dif-fering largely on the weightage given to thecladistic or phenetic relationship. There have been suggestions to abandonthe hierarchical contemporary classifica-tions based on the Linnaean system, whichemploys various fixed ranks in an estab-lished conventional sequence with a ‘phy-logenetic taxonomy’ in which monophyleticgroups would be unranked names, definedin terms of a common ancestry, and diag-nosed by reference to synapomorphies (deQueiroz and Gauthier, 1990; Hibbett andDonoghue, 1998).

Classification not only helps in the place-ment of an entity in a logically organizedscheme of relationships, it also has a greatpredictive value. The presence of a valuablechemical component in one species of a par-ticular genus may prompt its search in otherrelated species. The more a classificationreflects phylogenetic relationships, the morepredictive it is supposed to be. The meaningof a natural classification is gradually los-ing its traditional sense. A ‘natural classifi-cation’ today is one visualized as truly phy-logenetic, establishing monophyletic groupsmaking fair use of the phenetic informationso that such groups also reflect a pheneticrelationship (overall similarity) and the clas-sification represents a reconstruction of theevolutionary descent.

Aims of SystematicsThe activities of plant systematics are ba-sic to all other biological sciences and, inturn, depend on the same for any additionalinformation that might prove useful in con-structing a classification. These activitiesare directed towards achieving theundermentioned aims:

1. To provide a convenient method ofidentification and communication. Aworkable classification having the taxaarranged in hierarchy, detailed anddiagnostic descriptions are essential


for identification. Properly identifiedand arranged herbarium specimens,dichotomous keys, polyclaves and com-puter-aided identification are impor-tant aids for identification. The Code(ICBN), written and documentedthrough the efforts of IAPT (Interna-tional Association of Plant Taxonomy),helps in deciding the single correctname acceptable to the whole botani-cal community.

2. To provide an inventory of the world’sflora. Although a single world Flora isdifficult to come by, floristic records ofcontinents (Continental Floras; cf.Flora Europaea by Tutin et al.), regionsor countries (Regional Floras; cf. Floraof British India by J. D. Hooker) andstates or even counties (Local Floras;cf. Flora of Delhi by J. K. Maheshwari)are well documented. In addition, WorldMonographs for selected genera (e.g.,The genus Crepis by Babcock) and fami-lies (e.g., Das pflanzenreich ed. byA. Engler) are also available.

3. To detect evolution at work; to recon-struct the evolutionary history of theplant kingdom, determining the se-quence of evolutionary change andcharacter modification.

4. To provide a system of classificationwhich depicts the evolution within thegroup. The phylogenetic relationshipbetween the groups is commonly de-picted with the help of a phylogram,wherein the longest branches repre-sent more advanced groups and theshorter, nearer the base, primitiveones. In addition, the groups are rep-resented by balloons of different sizesthat are proportional to the number ofspecies in the respective groups. Sucha phylogram is popularly known as abubble diagram. The phylogenetic re-lationship could also be presented inthe form of a phylogenetic tree (withvertical axis representing the geologi-cal time scale), where existing speciesreach the top and the bubble diagrammay be a cross-section of the top with

primitive groups towards the centreand the advanced ones towards theperiphery.

5. To provide an integration of all availa-ble information. To gather informationfrom all the fields of study, analysingthis information using statistical pro-cedures with the help of computers,providing a synthesis of this informa-tion and developing a classificationbased on overall similarity. Thissynthesis is unending, however,since scientific progress will continueand new information will continue topour and pose new challenges fortaxonomists.

6. To provide an information reference,supplying the methodology for informa-tion storage, retrieval, exchange andutilization. To provide significantlyvaluable information concerning en-dangered species, unique elements,genetic and ecological diversity.

7. To provide new concepts, reinterpretthe old, and develop new procedures forcorrect determination of taxonomicaffinities, in terms of phylogeny andphenetics.

8. To provide integrated databases includ-ing all species of plants (and possiblyall organisms) across the globe. Sev-eral big organizations have come to-gether to establish online searchabledatabases of taxon names, images, de-scriptions, synonyms and molecularinformation.

Advancement Levels inSystematicsPlant systematics has made considerablestrides from herbarium records to data-banks, recording information on everypossible attribute of a plant. Because of ex-treme climatic diversity, floristic variabil-ity, inaccessibility of certain regions andeconomic disparity of different regions, thepresent-day systematics finds itself indifferent stages of advancement in differentparts of the world. Tropical Asia and tropical


Africa are amongst the richest areas of theworld in terms of floristic diversity butamongst the poorest as far as the economicresources to pursue complete documenta-tion of systematic information. The wholeof Europe, with more than 30 m squarekilometres of landscape and numerous richnations with their vast economic resources,have to account for slightly more than 6 thou-sand species of vascular plants. India, on theother hand, with meager resources, lessthan one tenth of landscape, has to accountfor the study of at least four times more ofthe vascular plants. A small country likeColombia, similarly, has estimated 4,5000different species, with only a few botaniststo study the flora. Great Britain, on the otherhand, has approximately 1370 taxa (Wood-land, 1991), with thousands of professionaland amateur botanists available to documentthe information. It is not strange, as such,that there is lot of disparity in the level ofadvancement concerning knowledge aboutrespective floras. Taxonomic advancementtoday can be conveniently divided into fourdistinct phases encountered in differentparts of the world:

Exploratory or Pioneer PhaseThis phase marks the beginning of plant tax-onomy, collecting specimens and buildingherbarium records. The few specimens of aspecies in the herbarium are the only recordof its variation. These specimens are, how-ever, useful in a preliminary inventory offlora through discovery, description, namingand identification of plants. Here, morphol-ogy and distribution provide the data onwhich the systematists must rely. Taxo-nomic experience and judgement are par-ticularly important in this phase. Most ar-eas of tropical Africa and tropical Asia arepassing through this phase.

Consolidation or SystematicPhaseDuring this phase, herbarium records areample and enough information is availableconcerning variation from field studies.

This development is helpful in the prepa-ration of Floras and Monographs. It also aidsin better understanding of the degree ofvariation within a species. Two or more her-barium specimens may appear to be suffi-ciently different and regarded as belongingto different species on the basis of a fewavailable herbarium records, but only a fieldstudy of populations involving thousands ofspecimens can help in reaching at a betterunderstanding of their status. If there areenough field specimens to fill in the gapsin variation pattern, there is no justifica-tion in regarding them as separate species.On the other hand, if there are distinct gapsin the variation pattern, it strengthenstheir separate identity. In fact, many plants,described as species on the basis of limitedmaterial in the pioneer phase, are found tobe variants of other species in the consoli-dation phase. Most parts of central Europe,North America and Japan are experienc-ing this phase.

Experimental orBiosystematic PhaseDuring this phase, the herbarium recordsand variation studies are complete. In addi-tion, information on biosystematics (stud-ies on transplant experiments, breedingbehaviour and chromosomes) is also avail-able. Transplant experiments involve col-lecting seeds, saplings or other propagulesfrom morphologically distinct populationsfrom different habitats and growing themunder common environmental conditions. Ifthe differences between the original popu-lations were purely ecological, the differ-ences would disappear under a common en-vironment, and there is no justification inregarding them as distinct taxonomic enti-ties. On the other hand, if the differencesstill persist, these are evidently geneticallyfixed. If these populations are allowed to growtogether for several years, their breedingbehaviours would further establish their sta-tus. If there are complete reproductive bar-riers between the populations, they will failto interbreed, and maintain their separate


identity. These evidently belong to differentspecies. On the other hand, if there is noreproductive isolation between them, overthe years, they would interbreed, form in-termediate hybrids, which will soon fill thegaps in their variation. Such populationsevidently belong to the same species andbetter distinguished as ecotypes, subspeciesor varieties. Further chromosomal studiescan throw more light on their affinities andstatus. Central Europe has reached thisphase of plant systematics.

Encyclopaedic orHolotaxonomic PhaseHere, not only the previous three phases areattained, but information on all the botani-cal fields is also available. This information

is assembled, analyzed, and a meaningfulsynthesis of analysis is provided for under-standing phylogeny. Collection of data,analysis and synthesis are the jobs of an in-dependent discipline of systematics, referredto as numerical taxonomy.

The first two phases of systematics areoften considered under alpha-taxonomy andthe last phase under omega-taxonomy. Atpresent, only a few persons are involved inencyclopaedic work and that too, in a few iso-lated taxa. It may thus be safe to concludethat though in a few groups omega-taxonomyis within reach, for the great majority ofplants, mainly in the tropics, even the ‘al-pha’ stage has not been crossed. The totalintegration of available information for theplant kingdom is, thus, only a distant dreamat present.

Nomenclature deals with the application of acorrect name to a plant or a taxonomic group.In practice, nomenclature is often combinedwith identification, since while identifying anunknown plant specimen, the author choosesand applies the correct name. The favouritetemperate plant is correctly identifiedwhether you call it ‘Seb‘ (vernacular Hindiname), Apple, Pyrus malus or Malus malus, butonly by using the correct scientific nameMalus domestica does one combine identifi-cation with nomenclature. The current ac-tivity of botanical nomenclature is governedby the International Code of Botanical Nomen-clature (ICBN) published by the InternationalAssociation of Plant Taxonomy (IAPT). TheCode is revised after changes at each Inter-national Botanical Congress. The naming ofthe animals is governed by the InternationalCode of Zoological Nomenclature (ICZN) andthat of bacteria by the International Code forthe Nomenclature of Bacteria (ICNB; nowknown as Bacteriological Code-BC). Virusnomenclature is governed by InternationalCode of Virus Classification and Nomencla-ture (ICVCN). Naming of cultivated plants isgoverned by the International Code of Nomen-clature for Cultivated Plants (ICNCP), whichis largely based on ICBN with a few additionalprovisions. Whereas within the provisions ofa particular code no two taxa can bear thesame correct scientific name, same names

are allowed across the codes. The genericname Cecropia applies to showy moths as alsoto tropical trees. Genus Pieris, similarly, re-fers to some butterflies and shrubs.

During the last decade, there have beenattempts at developing unified code for all liv-ing organisms, for convenient handling ofcombined database for all organisms. DraftBioCode and PhyloCode, have been con-certed efforts in this direction, but it will takea long time before acceptability of theseendeavours can be determined.

NEED FOR SCIENTIFIC NAMESScientific names formulated in Latin are pre-ferred over vernacular or common namessince the latter pose a number of problems:

1. Vernacular names are not available forall the species known to man.

2. Vernacular names are restricted intheir usage and are applicable in asingle or a few languages only. Theyare not universal in their application.

3. Common names usually do not provideinformation indicating family or ge-neric relationship. Roses belong to thegenus Rosa; woodrose is a member ofthe genus Ipomoea and primrose be-longs to the genus Primula. The threegenera, in turn, belong to three differ-ent families—Rosaceae, Convolvu-

Chapter 2

Botanical Nomenclature


laceae and Primulaceae, respectively.Oak is similarly common name for thespecies of genus Quercus, but Tanbarkoak is Lithocarpus, poison oak a Rhus,silver oak a Grevillea and Jerusalemoak a Chenopodium.

4. Frequently, especially in widely distrib-uted plants, many common namesmay exist for the same species in thesame language in the same or differ-ent localities. Cornflower, bluebottle,bachelor‘s button and ragged robin allrefer to the same species Centaureacyanus.

5. Often, two or more unrelated speciesare known by the same common name.Bachelor‘s button, may thus beTanacetum vulgare, Knautia arvensis orCentaurea cyanus. Cockscomb, is simi-larly, a common name for Celosiacristata but is also applied to a seaweedPloca-mium coccinium or to Rhinanthusminor.

Why Latin?Scientific names are treated as Latin regard-less of their origin. It is also mandatory tohave a Latin diagnosis for any new taxonpublished 1 January 1935 onwards. The cus-tom of Latinized names and texts originatesfrom medieval scholarship and custom con-tinued in most botanical publications untilthe middle of nineteenth century. Descrip-tions of plants are not written in classicalLatin of Cicero or of Horace, but in the ‘lin-gua franca’ spoken and written by scholarsduring middle ages, based on popular Latinspoken by ordinary people in the classicaltimes. The selection has several advantagesover modern languages: i) Latin is a dead lan-guage and as such meanings and interpre-tation are not subject to changes unlike, En-glish and other languages; ii) Latin is spe-cific and exact in meaning; iii) grammaticalsense of the word is commonly obvious (whitetranslated as album-neuter, alba-feminineor albus- masculine); and iv) Latin languageemploys the Roman alphabet, which fits wellin the text of most languages.

DEVELOPMENT OF BOTANICALCODEFor several centuries, the names of plantsappeared as polynomials—long descriptivephrases, often difficult to remember. A spe-cies of willow, for example, was named Salixpumila angustifolia altera by Clusius in hisherbal (1583). Casper Bauhin (1623) intro-duced the concept of Binomial nomenclatureunder which the name of a species consistsof two parts, the first the name of the genusto which it belongs and the second the spe-cific epithet. Onion is thus appropriatelynamed Allium cepa, Allium being the genericname and cepa the specific epithet. Bauhin,however, did not use binomial nomenclaturefor all the species and it was left to CarolusLinnaeus to firmly establish this system ofnaming in his Species plantarum (1753). Theearly rules of nomenclature were set forth byLinnaeus in his Critica botanica (1737) andfurther amplified in Philosophica botanica(1751). A. P. de Candolle, in his Theorieelementaire de la botanique (1813), gave ex-plicit instructions on nomenclatural proce-dures, many taken from Linnaeus. Steudel,in Nomenclator botanicus (1821), providedLatin names for all flowering plants knownto the author together with their synonyms.

The first organized effort towards the de-velopment of uniform botanical nomencla-ture was made by Alphonse de Candolle, whocirculated a copy of his manuscript Lois de lanomenclature botanique. After deliberations ofthe First International Botanical Congress atParis (1867), the Paris Code, also known as‘de Candolle rules‘ was adopted. Linnaeus(1753) was made the starting point for plantnomenclature and the rule of priority wasmade fundamental. Not satisfied with theParis Code, the American botanists adopteda separate Rochester Code (1892), which in-troduced the concept of types, strict applica-tion of rules of priority even if the name wasa tautonym (specific epithet repeating thegeneric name, e.g. Malus malus).

The Paris Code was replaced by the ViennaCode (1905), which established Speciesplantarum (1753) of Linnaeus as the starting

ContentsPreface1. Plants, Taxonomy and systematicsPlants and Kingdoms of LifeTwo Kingdom SystemTwo Empires Three KingdomsFive Kingdom SystemSix or Seven Kingdoms?The Plant Kingdom

Taxonomy and SystematicsBasic Components (Principles) of SystematicsAims of SystematicsAdvancement Levels in Systematics

2. Botanical NomenclatureNeed for Scientific namesWhy Latin?

Development of Botanical CodeContents of Botanical CodePreamblePrinciples of ICBNNames of TaxaThe Type MethodAuthor CitationPublication of NamesRejection of NamesPrinciple of PriorityNames of HybridsNames of Cultivated Plants

Unified Biological NomenclatureDraft BioCodePhyloCode

3. Hierarchical ClassificationTaxonomic groups, categories and ranksUtilization of categoriesSpecies conceptInfraspecific ranksGenusFamily

4. Descriptive TerminiologyHabit and life spanHabitatRootsStemsLeavesLeaf arrangementLeaf durationLeaf incisionStipulesLeaf shapeLeaf marginLeaf baseLeaf apexLeaf surfaceVenation

InflorescenceRacemose typesCymose typesSpecialized types

FlowerCalyxCorollaPerianthAndroeciumGynoecium

FruitSimple fruitsAggregate fruitsMultiple fruits

Floral formulaFloral diagram

5. Process of IdentificationSpecimen preparationFieldworkEquipmentCollectionPressingHandling special groupsDrying

Herbarium methodsBotanical gardensHerbariaPest ControlVirtual herbarium

Identification methodsTaxonomic literatureTaxonomic keysComputers in identificationInteractive keys Id

6. Variation, Biosystematics, Population Genetics and EvolutionTypes of variationDevelopmental variationEnvironmental variationGenetic variation

Variance analysisReproductive systemsOutbreedingInbreedingApomixis

Population geneticsAllele frequenciesMating systemsHardy-Weinberg law

EvolutionMutationMigrationRandom genetic driftNatural selectionMolecular evolutionNeutral theory of evolutionSpeciation

7. Taxonomic EvidenceMorphologyHabitUnderground partsLeavesFlowersFruits

AnatomyWood anatomyTrichomesEpidermal featuresLeaf anatomyFloral anatomy

EmbryologyFamilies marked out by distinct embryological featuresSpecific examples of the role of embryological data

PalynologyPollen aggregationPollen wallPollen aperture

Micromorphology and UltrastructureMicromorphologyUltrastructure

ChromosomesChromosomal numberChromosomal structureChromosomal behaviour

ChemotaxonomyPrimary metabolitesSecondary metabolitesNon-semantide MacromoleculesProteins

Molecular systematicsMolecular evolutionLocation of molecular dataMolecular techniquesDNA polymorphismExamples of molecular studiesGene trees

8. Developing ClassificationsPhenetic methodsPrinciples of taxometrics

Cladistic methodsPhylogenetic termsPhylogenetic diagramsPhylogeny and classification

Phylogenetic data analysisTaxa-Operational UnitsCharactersMeasure of similarityThe Consensus treeAutomated treesGene trees and species treesDeveloping classification

9. Phylogeny of AngiospermsOrigin of AngiospermsWhat are Angiosperms?What is the age of Angiosperms?What is the place of their origin?Are angiosperms monophyletic or polyphyletic?What are the possible ancestors?Origin of monocotyledons

Basal living angiospermsCasuarinaceaeMagnoliidsPaleoherbs

Evolutionary trendsCoevolution with animalsBasic evolutionary trendsXylem evolutionStamen evolutionPollen grain evolutionCarpel evolutionEvolution of inferior ovary

10. Systems of ClassificationClassifications based on gross morphologyPreliterate mankindEarly literate civilisationsMedieval BotanyRenaissance

Sexual SystemCarolus Linnaeus

Natural SystemsMichel AdansonJean B. P. Lamarckde Jussieu familyde Candolle familyRobert BrownGeorge Bentham and Sir J. D. Hooker

Phylogenetic SystemsTransitional SystemsIntentional phylogenetic systemsModern phylogenetic systems

11. Families of PteridophytesLycopodiophtesLycopodiaceaeSelaginellaceaeIsoetaceae

PsilopsidaOphioglossaceaePsilotaceae

EquisetopsidaEquisetaceae

PteropsidaOsmundaceaeMarsileaceaeSalviniaceaeCyatheaceaePteridaceaeAspleniaceaeDryopteridaceaePolypodiaceae

12. Families of GymnospermsCycadalesCycadaceaeZamiaceae

GinkgoalesGinkgoaceae

ConiferalesPinaceaeCupressaceaePodocarpaceaeAraucariaceaeTaxaceae

GnetalesEphedraceaeGnetaceae

13. Major Families of AngiospermsAngiosperms roll of honourChloranthidaeAmborellaceaeChloranthaceaeAustrobaileyaceaeWinteraceaeIlliciaceaeCabombaceaeNymphaeaceaeCeratophyllaceae

MagnoliidaeMagnoliaceaeDegeneriaceaeAnnonaceaeCalycanthaceaeLauraceaeWinteraceaeSaururaceaePiperaceae

AlismatidaeAcoraceaeAraceaeButomaceaeAlismataceaeHydrocharitaceaePotamogetonaceae

LiliidaePandanaceaeDioscoreaceaeSmilacaceaeLiliaceaeOrchidaceaeIridaceaeAsphodelaceaeAlliaceaeSubfamilyAgavaceae

CommelinidaeArecaceaeCommelinaceaeMusaceaeZingiberaceaeCannaceaeJuncaceaeCyperaceaePoaceae

RanunculidaePaeoniaceaeBerberidaceaeRanunculaceaePapaveraceae

HamamelididaeSaxifragaceaeFagaceaeBetulaceaeCasuarinaceae

CaryophyllidaePortulacaceaeCactaceaeNyctaginaceaeAizoaceaeChenopodiaceaeAmaranthaceaeCaryophyllaceaePolygonaceaeDroseraceae

RosidaeCelastraceaeViolaceaeSalicaceaeCucurbitaceaeClusiaceaeEuphorbiaceaeOxalidaceaeZygophyllaceaeGeraniaceaeRosaceaeFabaceaeMyrtaceaeLythraceaeOnagraceae

MalvidaeMalvaceaeGrewiaceaeDipterocarpaceaeRhamnaceaeUlmaceaeMoraceaeUrticaceaeRafflesiaceaeCapparaceaeCleomaceaeBrassicaceaeRutaceaeMeliaceaeAnacardiaceaeSapindaceae

AsteridaeHydrangeaceaeCornaceaeBalsaminaceaePolemoniaceaeEbenaceaeSapotaceaePrimulaceaeEricaceaeAdoxaceaeApiaceaeAraliaceaeAsteraceae

LamiidaeSolanaceaeConvolvulaceaeBoraginaceaeRubiaceaeApocynaceaePlantaginaceaeLamiaceaeVerbenaceaeBignoniaceaeAcanthaceaeScrophulariaceae

References

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