Phylogeny and evolution of angiosperms
2006; Wiley; Volume: 22; Issue: 1 Linguagem: Inglês
10.1111/j.1096-0031.2006.00084.x
ISSN1096-0031
Autores Tópico(s)Plant and Fungal Species Descriptions
ResumoPhylogeny & Evolution of Angiosperms . By Douglas E Soltis, Pamela S Soltis, Peter K Endress & Mark W Chase . Sinauer Associates , Inc. 2005 . 370 pp. $59.95 (pbk) ISBN: 0-87893-817-6 . E. O. Wilson wrote in reference to the interaction among scientists “Yet, oddly, there is very little science culture, at least in the strict tribal sense. Few rites are performed to speak of. There is, at most, only a smattering of icons. One does, however, hear a great deal of petty bickering over territory and status. The social organization of science most resembles a loose confederation of petty fiefdoms.” (Wilson, 1998, p. 57). Too often, Wilson is correct on this point. Nevertheless there have been episodes in the history of scientific inquiry in which the “petty fiefdoms” have united to address fundamental mysteries of science. The revolution in atomic science that took place at the laboratories at Los Alamos, New Mexico toward the end of the Second World War was just such a collaboration. I am sure to many of the scientists involved, this revolution was driven by the thrill of discovery; but the greater impetus was certainly the need of a desperate wartime government to end the deadliest military stalemate of the twentieth century. Another such collaboration arose in the 1990s by plant systematics seeking not to end a destructive global war, but rather to address what Darwin referred to as an “abominable mystery”: the origin and diversification of the angiosperms. These 291 collaborators are collectively cited as the Angiosperm Phylogeny Group. The results of this effort have (fortunately) not been globally cataclysmic, but perhaps as scientifically revolutionary as the discoveries at Los Alamos. “Phylogeny and Evolution of Angiosperms” presents the major findings of this effort. Unlike many such books, it is no endnote to a finished project, but rather, a dynamic and synoptic state-of-the-union of the ongoing effort by many botanists to reach the consilience that E. O. Wilson entreated, in determining the phylogeny of the angiosperms and classifying them accordingly. While this effort represents a major triumph of the new molecular systematics, “Phylogeny and Evolution of Angiosperms” pays due tribute to the attempts by others (notably Cronquist, 1981 and Takhtajan, 1997) to achieve such a classification without the aid of molecules or phylogenetics. The single most notable aspect of this book is how broad it is in its scope, including careful consideration of numerous classes of data: DNA and RNA sequences, fossils, morphological, ecological, anatomical, palynological, ontogenetic, cytological, biochemical, developmental genetic, and genomic characters. In Chapter 1, Relationships of the Angiosperms to Other Seed Plants, competing hypotheses of seed plant phylogeny are considered in turn, and the merits of each examined. From the beginning of the book, the utility of different data sets is evaluated at different orders of hierarchy. At this level of phylogeny, DNA sequence data and morphology have been used to test evolutionary hypotheses. For seed plant phylogeny, the necessity of incorporating fossil evidence is made abundantly clear, as many of the putative sister-lineages to the flowering plants are extinct. Hypotheses of the origin of the flower are evaluated. While the question, “Which lineage is sister to the angiosperms?” remains unanswered, each of the best candidates is examined including the Caytoniales, Bennettitales, Pentoxylon and Glossopterids. In the title, “Phylogeny and Evolution of Angiosperms”, the phylogeny most often considered is the 567 taxon, three-gene phylogeny of Soltis et al. (2000). However, a multitude of other phylogenetic hypotheses are taken into account. Chapter 2 is an overview of the phylogeny of flowering plants in which other major attempts to infer an angiosperm phylogeny by previous authors are discussed, notably the morphological studies of Donoghue and Doyle (1989) and Loconte and Stevenson (1991), and the seminal, ambitiously collaborative 499 rbcL sequence analysis of Chase et al. (1993). The major clades of the angiosperms recognized in this book are compared to the classical systems of Dahlgren, Cronquist, Takhtajan & Thorne. Various implications of the phylogeny such as classification, rate and timing of angiosperm diversification are discussed in depth. Setting the stage for following chapters, this chapter ends with a “Future Studies” section, reminding the reader that there is still work to do, in this case adding taxa and data to analyses, incorporating morphology and other non-DNA characters, integrating fossils, examining character evolution in major clades, and the creation of “megatrees” that incorporate all angiosperm taxa. The value and methodology of this last goal may be the subject of considerable debate, but it has come to the forefront of “deep” phylogenetic study and merits inclusion in this chapter. Chapters 3–9 follow the spine of the tree, summarizing evidence supporting major lineages and exploring character evolution implied by the tree topology: Ch. 3—basal angiosperms, Ch. 4—monocots, Ch. 5—early diverging eudicots, Ch. 6—core eudicots, Ch. 7—Caryophyllales, Ch. 8—Rosids, and Ch. 9—Asterids. The format of these chapters is consistent. Competing and corroborating evidence for evolutionary hypotheses is followed by a discussion of topology and synapomorphies characterizing important nodes. Many of the relationships discovered are surprising, such as the inclusion of Paeoniaceae in Saxifragales. In each case, the authors examine possibly overlooked characters supporting such inclusions, but also discuss characters that disagree with the best phylogenetic hypothesis. The evolution of features characterizing taxa receives special attention in each chapter, even when these character transformations are homoplastic, such as stamen phyllotaxis in the basal angiosperms. Chapter 3: Basal Angiosperms is significantly longer than the other chapters given the relatively small number of taxa included. However, a great deal of the confusion and conflict has centered on the basal nodes of the angiosperm phylogeny. Resolving these nodes is important in elucidating the most fundamental questions on the origin of angiosperms, and as such, lengthy discussion is merited. On the other hand, Chapter 9: Asterids could be longer given the diversity of the group. It is perhaps only a small detraction given the scope of the work, but the acceptance of both Apiaceae and Arialaceae here conflicts with other recent assessments that include members of the former Araliaceae within Apiaceae (Judd et al., 1999). These are diverse and well-known families. Justification for this taxonomic decision would be helpful to the reader working outside of Apiales in deciding how to teach these taxa in plant systematics courses. Chapter 10: Angiosperm Classification discusses the use of Linnaean versus rank-free systems, and justifies the ordinal classification proposed by APG (1998) and APG II (2003). It concludes with a table of the orders of angiosperms and the taxa that have been placed within them. This chapter is indispensable to the mission of the book, but to my mind, is misplaced. The four pages discussing the classification adopted here could easily be placed in the second chapter, and the table of orders placed as an appendix referenced in Ch. 2. For those not thoroughly familiar with the APG II classification, this rearrangement might relieve some of the confusion resulting from the optimization of characters on a phylogeny where the terminals are not families but representative genera, and it is unclear which families were included in the phylogeny. Chapters 11–13 are specifically concerned with character evolution in the angiosperms. Chapter 11: Parallel and Convergent Evolution discusses three adaptations that have arisen convergently in different angiosperm clades: parasitism, carnivory, and C4 photosynthesis. While many characters have arisen convergently in the angiosperms, clearly the discussion of all of these is beyond the scope of a single volume. These three topics are interesting representatives of the kinds of adaptations that large-scale phylogenies may be used to address. Chapter 12: Floral Diversification outlines the ways in which floral whorls may vary among lineages, the ecological and genetic causes of this variation, and the pattern of diversification evident from the angiosperm phylogeny. Chapter 13: Evolution of Genome Size addresses the hypotheses that early angiosperms had less nuclear genetic material than many of the derived groups, and discusses the mechanisms by which the amount of DNA may increase or decrease within a lineage. This is a notoriously complex topic, which the authors deal with concisely without oversimplifying. Again, the final three chapters end in a “Future Studies” section. These three chapters may be of the most general interest, in that many of the topics included are relevant to any flowering plant systematist working in many smaller groups. An appendix is included of the primary phylogenetic hypothesis upon which the rest of the volume is based. “Phylogeny and Evolution of Angiosperms” will likely be considered a necessary reference in the library of most plant systematists. It is encyclopedic in its treatment of the subject matter and the lengthy list of works cited make it an excellent source book for anyone hoping to begin broad phylogenetic study. However, the scope of this book is so ambitious that it could not stand alone as a classroom text, except in the most advanced graduate courses. To fully comprehend this excellent treatment of multitudes of characters and taxa, one must be well versed in many botanical disciplines, from paleobotany to genomics. I found myself continually referring to other texts just to keep up with the lightning pace of the prose. This is hardly a condemnation, in that for a work of this breadth to be comprehensive, it would have to be much longer than would be acceptable to most publishers, and its cost to the consumer would almost certainly be prohibitive from a sales perspective. At the current price of $59.95 it is a bargain. In regard to the complexity of supporting evidence, the use of figures could be somewhat improved. Many of the figures are plates of plants or parts of plants comprising the lineage of interest. Often, it may be more helpful to replace these with figures of synapomorphic characters uniting clades. For instance, it may be more helpful to have a figure of the morphological and anatomical synapomorphies of the core Caryophyllales (which are numerous) than a plate of illustrated members of this section. Such a figure would reduce the necessity of enumerating synapomorphies in text as they could be included in the figure caption. Perhaps the most refreshing aspect of “Phylogeny and Evolution of Angiosperms” is the repeated focus on future inquiry and the unknown. The authors of this book were all members of the first APG and (I well imagine) devoted their professional lives thoroughly to its goals. They would certainly be justified in trumpeting the successes of their work. However, the tone throughout is considered and cautious, reflecting the dynamic nature of ongoing discovery and lingering uncertainty. Flowering plant systematics is a wonderfully messy discipline, in that plants are subject to a multitude of evolutionary processes that complicate phylogenetic analysis and classification. This biological untidiness motivates many botanists to get out of bed in the morning. While astounding progress has been made in the past 12 years in elucidating flowering plant relationships, there is still so much more to do. This book doesn't sweep any of the mess under the rug, maintaining the spirit of intellectual honesty notable in the following passage: “The 1990s and early 2000s saw enormous progress in several areas, including (1) elucidating important patterns of morphological development, (2) recovering and placing ancient angiosperm fossils (see Crepet, 2000; Crane et al., 2004), (3) identifying the most ancient clades of extant angiosperms and reconstructing the likely features of the earliest flowering plants, and (4) elucidating some of the key organ identity genes involved in floral development. Nonetheless, the origins of the angiosperms remains a monumental problem; the abominable mystery is far from solved” p. 89
Referência(s)