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Plant Taxonomy

Plant Taxonomy: The Systematic Evaluation of Comparative Data

Tod F. Stuessy
Copyright Date: 2009
Edition: 2
Pages: 568
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  • Book Info
    Plant Taxonomy
    Book Description:

    The field of plant taxonomy has transformed rapidly over the past fifteen years, especially with regard to improvements in cladistic analysis and the use of new molecular data. The second edition of this popular resource reflects these far-reaching and dramatic developments with more than 3,000 new references and many new figures. Synthesizing current research and trends, Plant Taxonomy now provides the most up-to-date overview in relation to monographic, biodiversity, and evolutionary studies, and continues to be an essential resource for students and scholars.

    This text is divided into two parts: Part 1 explains the principles of taxonomy, including the importance of systematics, characters, concepts of categories, and different approaches to biological classification. Part 2 outlines the different types of data used in plant taxonomic studies with suggestions on their efficacy and modes of presentation and evaluation. This section also lists the equipment and financial resources required for gathering each type of data. References throughout the book illuminate the historical development of taxonomic terminology and philosophy while citations offer further study. Plant Taxonomy is also a personal story of what it means to be a practicing taxonomist and to view these activities within a meaningful conceptual framework. Tod F. Stuessy recalls the progression of his own work and shares his belief that the most creative taxonomy is done by those who have a strong conceptual grasp of their own research.

    eISBN: 978-0-231-51864-2
    Subjects: Botany & Plant Sciences, Biological Sciences, Ecology & Evolutionary Biology

Table of Contents

  1. Front Matter
    (pp. i-vi)
  2. Table of Contents
    (pp. vii-xiv)
  3. Preface to the First Edition
    (pp. xv-xvi)
  4. Preface to the Second Edition
    (pp. xvii-xviii)
  5. Acknowledgments for the First Edition
    (pp. xix-xx)
  6. Acknowledgments for the Second Edition
    (pp. xxi-xxvi)
  7. PART ONE Principles of Taxonomy

    • SECTION 1 The Meaning of Classification

      • [SECTION 1 Introduction]
        (pp. 3-4)

        Taxonomy is dynamic, beautiful, frustrating, and challenging all at the same time (fig. 1.1). It is demanding philosophically and technically, yet it offers intellectual rewards to the able scholar and scientist. It can be manifested in works of incredible detail as well as in logical and philosophical conceptualizations about the general order of things. It has strong implications for interpreting the reality of the world as we can ever hope to know it.

        Because taxonomy has deep historical roots, the past is never escaped. This places an increasing burden upon practitioners to understand old and new material. The past must...

      • CHAPTER 1 A Few Definitions
        (pp. 5-12)

        Taxonomy has had various meanings over the past 150 years, and particular confusion with systematics has prevailed. Systematics no doubt was used very early as “a casual self-evident term” (Mason 1950:194) to refer to the ordering of organisms into rudimentary classifications. This activity has occurred ever since people have lived on earth (Raven, Berlin, and Breedlove 1971). The early documented use of the term systematics (as systematic botany) can be traced at least as far back as Linnaeus (1737a, 1751, 1754), and it has persisted to the present day although in modified form. Linnaeus (1737a:3) stated that “we reject all...

      • CHAPTER 2 The Relevance of Systematics
        (pp. 13-18)

        Because of the close relationship of taxonomy to systematics, a few comments on the relevance of the latter are appropriate. It would be surprising if systematics, which deals directly with organic diversity, did not relate to every aspect of human endeavor. The impact of systematics upon society is substantial and most easily reflected in satisfying our intellectual curiosity about the world in which we live, formulating principles and methods of classification applicable to many human needs and activities, helping preserve the world’s organic diversity for aesthetic and economic reasons, and more directly in developing economic potentials.

        There is no general...

      • CHAPTER 3 The Importance and Universality of Classification
        (pp. 19-24)

        Of the numerous important contributions that systematics makes to society and biology, none is more significant than that provided by classification (and its theoretical and methodological umbrella, taxonomy). Classification is a pervasive human quality “like the predisposition to sin, it accompanies us into the world at birth and stays with us to the end” (Hopwood 1959:230). Although it cannot be denied that the construction of classifications provides intellectual satisfaction for those who make them (J. A. Moore, in Warburton 1967), and, in my opinion, this by itself is justification enough, many more positive features of classification also exist. Heywood suggested...

      • CHAPTER 4 Characters
        (pp. 25-36)

        The construction of classifications with their many positive features depends upon a careful comparison of attributes of the organisms. It is not sufficient to state that “organism X is more similar to organism Y than either is to Z” without also expressing the particular reasons for this conclusion. Such expressions of relationship are based upon a comparison of features of the organisms (either clearly stated or intuitively evaluated) called taxonomic characters. As Kendrick expressed well: “Although a man can visually appreciate a very complex concept almost instantaneously, his much more limited capacity for verbal communication forces him to describe what...

    • SECTION 2 Different Approaches to Biological Classification

      • [SECTION 2 Introduction]
        (pp. 37-38)

        During the past 50 years, two new efforts toward classification have been advocated: phenetics and cladistics. These have been nothing short of revolutionary in the sense that they have forced us to think about what we really are doing in classification and to do it quantitatively (Stevens 2000a; Stuessy 2006). A comprehensive discussion of these and ancillary approaches to biological classification is needed, especially because of the breadth of the literature and development of different “schools,” each with definite (and sometimes dogmatic) viewpoints. Although it is impossible to know everything about all these issues, the student of modern plant taxonomy...

      • CHAPTER 5 The Anatomy of Classification and the Artificial Approach
        (pp. 39-44)

        The process of classification is viewed by different people in different ways, ranging from unfathomable intuitive art to objective, explicit, and testable science. I believe that it will be helpful to examine the reasons for the long-standing connection of taxonomy to art, as an aid to clarifying this relationship. The process of classification will also be analyzed in detail, followed by comments on the artificial approach.

        Classification is strongly aesthetic, particularly in phyletic approaches, and therein lies the artistic connection (Friedmann 1966). As Stearn aptly commented: “Aesthetic appreciation rests, I think, chiefly on a sense of form. The co-ordination of...

      • CHAPTER 6 Natural and Phyletic Approaches
        (pp. 45-50)

        Despite the widespread dissemination and acceptance of the Linnaean sexual system of classification, some workers never felt entirely satisfied with it. Although the artificial approach could not fail to allow all plants to be grouped with ease, the resulting groups of plants often seemed very different from each other in regard to features other than the sexual parts (fig. 6.1). Bernard de Jussieu (1699–1777), demonstrator of plants in the Royal Botanical Garden in Paris, arranged the plants in the Royal Garden and in Marie Antoinette’s garden in La Trianon at Versailles. Earlier the well-known Tournefort had been in charge...

      • CHAPTER 7 The Phenetic Approach
        (pp. 51-72)

        Not all taxonomists, however, have found the phyletic approach to classification satisfactory. Some workers, especially in the early 1960s (e.g., Sokal and Sneath 1963; Sneath and Sokal 1973) regarded this method as too subjective, and as evidence they pointed to different classifications generated by different taxonomists for the same sets of organisms. They gave striking examples of lumping vs. splitting in intuitive phyletic classification, especially in groups that are strongly inbreeding or with asexual nodes of reproduction (e.g., in Crataegus and Taraxacum). In these cases, widely divergent views have prevailed even with examination of more or less the same collections...

      • CHAPTER 8 The Cladistic Approach
        (pp. 73-110)

        Some workers have been dissatisfied with both the phyletic approach because of its intuitive (and presumably “less scientific”) nature and with phenetics because it has not been based on evolutionary thinking. For example, Bremer and Wanntorp (1978:322) commented on the traditional phyletic approach to classification that “such a system is not falsifiable, not truly part of science according to Popper [a philosopher of science], and in fact more a work of art, and as such highly personal and not repeatable.” Farris (1977a:848) commented that “there does not appear to be any justification for phenetic taxonomy as it is currently practiced.”...

      • CHAPTER 9 Evaluations of the Three Major Approaches and Explicit Phyletics
        (pp. 111-128)

        Before beginning a detailed evaluation of the three major approaches to biological classification (i.e., phyletics, phenetics, and cladistics), it is useful to set the stage by outlining the factors that have influenced their development.¹ Many of the ideas for the origin of phenetics and cladistics have been presented already in the previous chapters, but a summary for all approaches is needed here.

        Figure 9.1 shows the perceived needs that influenced development of the major approaches to biological classification and their relation to each other. Four principal needs can be documented. First is the need to cope with increasing levels of...

    • SECTION 3 Concepts of Categories

      • CHAPTER 10 The Taxonomic Hierarchy
        (pp. 131-136)

        In order for ranking to be achieved, a hierarchy of categories must be provided into which taxonomic units can be placed.¹ For organisms, such a structure is called the Linnaean hierarchy, after the Swedish botanist Carl Linnaeus (e.g., 1753, 1754), who first consistently used many of the categories we now employ. With inanimate objects, many different types of hierarchies, or sets of classes, are available for use. For the biotic world, we use principally one, and this rigidity prevails for at least three reasons: (1) for purposes of efficient and exact communication on a worldwide basis, one standard hierarchy is...

      • CHAPTER 11 The Species
        (pp. 137-152)

        The species is the fundamental category of the taxonomic hierarchy. Species are the “building bricks” in biological classification (Davis 1978:325) from which concepts of higher and lower groups are developed. “The species is a biological phenomenon that cannot be ignored. Whatever else the species might be, there is no question that it is one of the primary levels of integration in many branches of biology, as in systematics (including that of micro-organisms), genetics, and ecology, but also in physiology and in the study of behavior” (Mayr 1957a:iii). The species category is doubtless one of the oldest concepts used historically by...

      • CHAPTER 12 The Subspecies, Variety, and Form
        (pp. 153-162)

        Although in many cases the designation of species within a taxon is completely adequate to account for almost all of the meaningful patterns of morphological and other variation, in other cases it is not. In some situations, particularly those in which complex patterns of variation occur, there is a real need to circumscribe infraspecific taxa. This is especially important in the context of the local population as the site of evolutionary change (Ehrlich and Raven 1969; Levin 1993).

        The International Code of Botanical Nomenclature (McNeill et al. 2006) recommends use of no more than five infraspecific categories: subspecies, variety (varietas),...

      • CHAPTER 13 The Genus
        (pp. 163-172)

        The genus is the next principal category in the taxonomic hierarchy above the species. The International Code of Botanical Nomenclature (McNeill et al. 2006) allows several intervening categories also, viz., series, section (sectio), and subgenus, but these are not fundamental to the hierarchy and are not always used in classification within a particular group. They can be very helpful, however, especially in providing an infrageneric structure within large genera (e.g., in Silene, Caryophyllaceae, with more than 700 species; Greuter 1995). Their use is to be encouraged in certain situations (to be discussed in more detail later in this chapter).


      • CHAPTER 14 The Family and Higher Categories
        (pp. 173-178)

        To rise beyond the generic level in classification is to enter a world of much greater uncertainty. Families, orders, classes, divisions, kingdoms, and domains depart significantly from biological concerns at the populational level and force a treatment based almost entirely on comparative data that are often incomplete. Taxa at higher levels will be well-defined or ill-defined depending upon the group in question.

        Kingdoms of life used to be extremely well-defined, traditionally as plants and animals, but recent years have brought much change of viewpoint based especially on new molecular data. Whittaker (1969) suggested the now reasonably well-accepted concept of five...

  8. PART TWO Taxonomic Data

    • SECTION 4 Types of Data

      • CHAPTER 15 Morphology
        (pp. 183-198)

        It is no exaggeration to state that morphological data, based on the external form of organisms, have been, and still are, used most in plant classification. Morphological features have the advantage of being easily seen, and, hence, their variability has been much more appreciated than that of other kinds of features. This is especially true with herbarium material, on which a great deal of taxonomic work is based. The early plant taxonomists relied almost exclusively upon morphology to classify and identify the plants being sent to them from many parts of the world. As a result, the system of classification...

      • CHAPTER 16 Anatomy
        (pp. 199-210)

        Anatomy, or the internal form and structure of plant organs, is another classical source of data used in plant taxonomy. Anatomical data are often extremely useful in solving problems of relationships because they can often suggest homologies of morphological character states, and they can also help in the interpretation of evolutionary directionality (= polarity). Comparative anatomy is sometimes characterized as a sterile discipline, bereft of new advances, that has outlived its usefulness. Nothing could be further from the truth. A glance at the papers in symposia volumes (e.g., Robson, Cutler, and Gregory 1970; Baas 1982b; White and Dickison 1984; Rudall...

      • CHAPTER 17 Embryology
        (pp. 211-222)

        Features relating to the origin and development of the embryo in angiosperms have been used successfully to help determine taxonomic relationships. It is believed helpful to view embryology in the broad sense to encompass features of three generations: the old sporophyte, the gametophyte, and the new sporophyte and, hence, involving “the development of the entire ovule and anthers, including micro- and megasporogenesis, gametophytes, gametogenesis and growth of the embryo, endosperm, nucellus and integuments” (Cave 1948:344; see also Cave 1953). As Davis put it clearly, this includes “all processes and structures associated with sporogenesis, gametogenesis, and embryogeny” (1966:7). The close relationship...

      • CHAPTER 18 Palynology
        (pp. 223-238)

        Palynology, or the study of pollen grains and spores, could be regarded as simply one aspect of embryology instead of being treated separately. Because so much work has been done with pollen grains in taxonomy, far more in fact than with all other aspects of embryology combined, it makes more sense to regard this area as a separate source of comparative data. The field is relatively youthful, however, with the label palynology not having been coined until 1945 by Hyde and Williams. Palynology also obviously intergrades with pollination biology and reproductive biology, particularly in the area of pollen-stigma interactions and...

      • CHAPTER 19 Phytochemistry
        (pp. 239-254)

        Phytochemical data in taxonomy have inherent appeal by offering a look at relationships of plants via internal characters and at still another level of structural organization. Secondary metabolites (e.g., alkaloids and terpenoids) also have major ecological roles in the relation of plants to their environment. Certain kinds of phytochemical data, therefore, are likely to be of value in determining phylogeny, whereas others are of even greater value in understanding predator-prey and other ecological relationships. Through it all, phytochemical characters have continued to prove valuable in helping solve different kinds of taxonomic problems. It is clear that phytochemistry is here to...

      • CHAPTER 20 Cytology and Cytogenetics
        (pp. 255-272)

        Although cytology in a broad sense deals with all aspects of cells, in practice in taxonomic work, the focus has been mostly on chromosomes. Other features of cells, e.g., sieve-tube plastid variation, in this book are treated as ultrastructural data (Chapter 16). This also applies to the many intracellular features of single- or few-celled cyanobacteria and algae (e.g., Komárek and Cepák 1998). Cytogenetics in a broad sense is the study of chromosome number, structure, function, and behavior in relation to gene inheritance, organization and expression. Present cytogenetic work involving labelling parts of the genome (i.e., regions of chromosomes) with molecular...

      • CHAPTER 21 Molecular Biology
        (pp. 273-294)

        Of all the different sources of comparative data currently used in plant systematics, molecular biological data are among the most intriguing, exciting, and conspicuous. From understanding of the double helix structure of DNA more than 50 years ago by Watson and Crick (1953) came early interest in the potential of DNA data to reveal phylogenetic relationships (Zuckerkandl and Pauling 1965). The obvious challenge was how to get at the data. Early systematic efforts focused on DNA–DNA hybridization (Bendich and Bolton 1967), but these were never satisfying in plants due to technical difficulties and our lack of understanding of such...

      • CHAPTER 22 Genetics and Population Genetics
        (pp. 295-308)

        All the molecular biological methods now utilized for estimating relationships among species and higher taxa in an explicit phylogenetic, phenetic, or phyletic context can also be applied to revealing genetic affinities at the populational level. Earlier genetic studies relied on actual crossing programs to understand the patterns of inheritance of specific features. Because this was very time consuming, most systematists were content to assess lower-level relationships through morphology (especially morphometrics) and only to infer their genetic basis. Beginning with isozymes in the late 1960s (Lewontin and Hubby 1966), molecular tools became available to allow precise evaluations of genetic affinities among...

      • CHAPTER 23 Reproductive Biology
        (pp. 309-320)

        Plants do not live in isolation; they constantly interact with biotic and abiotic elements of their environment. Furthermore, they possess differences in life history strategies that allow them to adapt to their environment and survive. The reproductive syndrome of plants is an important facet of their adaptational response. Many aspects can be included here, but some types of data are more strictly ecological or evolutionary and are not useful for comparative taxonomic purposes. For example, the allocation of resources to vegetative vs. reproductive organs is of interest ecologically and evolutionarily (e.g., Abrahamson and Hershey 1977; Abrahamson 1979; Abrahamson and Caswell...

      • CHAPTER 24 Ecology
        (pp. 321-332)

        Ecological data are different from other types of comparative data in taxonomy. These deal not with features of the plants themselves, which are the macro- and microstructures discussed in the previous nine chapters, but rather with the plant-environment interactions (Izco 1980). These interactions are the net effects of all the features of the plant with all the aspects of the environment, and they are of two basic types: (1) with the abiotic part of the environment, such as soils, temperature, and moisture, and (2) with the biotic part of the environment, including aspects such as herbivores and competitors. Pollinators can...

    • SECTION 5 The Handling of Data

      • CHAPTER 25 The Gathering and Storage of Data
        (pp. 335-340)

        From a taxonomist’s point of view, it is depressing to reflect upon the mass of published data from cytology, chemistry, anatomy, DNA sequences, and other sources that exists for plants but is of marginal use for gaining systematic insights because of the small sample size or lack of adequate documentation provided. In taxonomic studies, therefore, it is imperative to pay close attention to several considerations when gathering comparative data (table 25.1).

        The first consideration in gathering comparative data is sampling. This aspect is usually done in the field, and for this reason, the investigator must have a clear idea of...

      • CHAPTER 26 The Presentation of Data
        (pp. 341-352)

        After data have been collected and measured, some means must be devised for reducing them so that relationships among taxa are demonstrated in an understandable fashion. Sometimes all that is needed is a simple listing of the raw data, but more frequently, some conversion is helpful, such as into means, ranges, or standard deviations, or even more complex statistics (see Tukey 1977; Sokal and Rohlf 1981a, 1994; Grafen and Hails 2002; Dytham 2003). For many systematists, however, a strict numerical treatment of data often is insufficient to illustrate relationships clearly. To comment on this point requires a short digression (also...

  9. Epilogue
    (pp. 353-354)

    Taxonomy is one of the most important of the biological sciences. Without the predictive framework of classification developed over the past 2000 years, human culture as we know it would have been very different and perhaps even still grossly underdeveloped. The need to understand the objects in our environment, both animate and inanimate, and to arrange these into a logical and predictive framework is essential to the human condition and doubtless fundamental to the development of language and of patterns of thinking in general.

    There is also a powerful human curiosity to understand and explain the diversity of life on...

  10. Literature Cited
    (pp. 355-484)
  11. Author Index
    (pp. 485-522)
  12. Taxon Index
    (pp. 523-532)
  13. Subject Index
    (pp. 533-539)