Plant Systematics: A Phylogenetic Approach
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Plant Systematics: A Phylogenetic Approach Customer Reviews
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PHYLOGENY AND NIRVANA
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Several colleagues have recently adopted, or plan to adopt the new textbook by JUDD, W. S., CAMPBELL, C. S., KELLOGG, E. A. & STEVENS, P. F. 1999. Plant systematics, a phylogenetic approach. ISBN 0-87893-404-9, for teaching vascular plant taxonomy. The book has some very useful introductory chapters on modern tools, which provide students with an insight on the applications of phytochemistry, mollecular biology and confection of cladograms.
Surely plant (and other) systematics bear on a traditional use of systems which have inherent flaws, given the tremendous diversity os species (or whatever you can call the final taxa) they deal with. The limitations of a patchy fossil record render phylogenetic approaches, however tempting their confection may be for a plant scientist in his search of a broader understanding, a kind of Nirvana that can never be completely conquered. We can know with some accuracy how long ago currently fossilized plants lived, but anyone familiar with the concept of convergence can hardly attribute affinities to a leaf imprint not attached to a flower or vice versa. Oddly enough, some of these concerns are addressed in Chapter 1 of the book, which is not consistent with the classification system proposed [since a large number of smaller but very important families was left out].
On p. 3 the book addresses the theory-neutral approach and clearly states it's intent to go further - into Phylogenetic interpretations. Conversely the most exhaustive numeric study of all species in a single extant genus, using all characters one can securely split into states, will shed light on their similarities, providing just another elegant and often valuable way to organize data, such as a cladogram. Distinguishing similarities reflecting true affinities from those brought about by convergence remains a cumbersome task which shall always rely on traditional methods.
The comment on p. 6 says: "We do not know the actual phylogeny of any nontrivial group of organisms [what would a trivial one be?], but instead must infer phylogenies from the data available to us." I have trouble agreeing with this point of view, since available data is admittedly patchy and often inconsistent. Paths in the true cladogram of evolution can not be retraced based on assumptions. We only have access to the dense upper surface of the crown, while the gross remainder of the tree's branches and trunk are obstructed from view. No matter from which angle one looks at it, Phylogeny draws on a generous dose of guesswork. On the practical purpose of classification, I cannot but paraphrase CRONQUIST (1988:12), one of the traditional taxonomists excommunicated in this book: "In taxonomy, consistency must always be secondary to the primary objective of recognizing natural groups on the basis of all available information".
Fitting the entire universe of traditional knowledge and current advances of plant systematics into a comprehensive book for students at any level poses obvious problems: How does one cope with limited space to organize the maelstrom of data? Our minds need to create categories in order to control storage and retreival of information. Obviously some omitting is inevitable, but at least the general idea of diversity must come across. In that sense I am especially intrigued by the comment by Michael Donoghue in the foreword "Students will readily appreciate the desirability of abandoning ranks altogether."
Following one of the modern trends, some groups of plants in the book's system, (for ex. used for Orchids in Dahlgren's treatment) are named using formal taxonomic rank, while other are not. If a group is recognized as separate, why not give it a rank? One inherent function of ranks is providing a common language - the only method of sharing knowledge currently used by humans. It must be recognized that the way in which ranks are currently applied is not problem-free: why must there be a defined number of them, let's say, between family and species? Rather than eliminating ranks, we should create new ways to apply them and see them.
No matter how deeply modern views have shifted, we can never entirely erase nor replace the results presented in old publications. Students need to know and understand important footsteps in 2 centuries of botanical investigation, which have paved the way toward current advances. We can now add new characters from an arsenal of chemical and mollecular data, ecological observations and a substantially improved matrix of geographic data. Regardless of academic rank, we are all students with a mission to discover and organize information and convey knowledge, not to ignore, misplace or ommit data. How can a student fit families like the Acanthochlamydaceae, Acoraceae, Boryaceae, Burmanniaceae, Corsiaceae, Costaceae, Didieraceae, Epacridaceae, Lemnaceae, Velloziaceae or Xyridaceae into such a system, when they are not even in the alphabetical index?
A good system must account for every component as best it can. Misplacing taxa (implicitly considered the most common flaw of traditional classifications) is still better than making-believe that odd parts don't exist. The argument of producing a textbook for undergraduate courses does not justify the omission of important plant families. Students deserve to start out at least with a complete set of families and the tools to recognize them. Even a great job of organizing a mere subset of information has very limited practical value, especially if Phylogeny is one of its main goals. Some of the smaller families which were left out are very important from both the taxonomic and the phytogeographic perspectives. Despite some hardships such as dichotomic keys starting with presence or absence of betalains, Cronquist's system remains the most recent comprehensive reference guide to the diversity of flowering plant families, simple enough to be used at the undergraduate level.
Though data from modern sources, such as molecular and chemical, are used in the introductory chapters, it is not quite clear how this data was usen in confecting the classification by JUDD et al., and there is no way of knowing whether the new system proposed shall hold its consistency after all omitted families of vascular plants are included in the data. |
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