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Diversity and Evolutionary Biology of Tropical Flowers.

One of the great joys of being a field botanist is to "understand" flowers: snapdragon and aconite and their co-evolutionary association with bumblebees, magnolias and water lilies with beetles, and skunk cabbage and Viburnum with flies. It is this unending fascination of the inseparable relationship of function to form, of process to structure, that fired Darwin's imagination and that of most ecologists ever since. Because floral ecology had its beginnings in Europe, fully 200 years ago, and the flowers of temperate lands are well known, an abundant and sophisticated literature on their floral ecology is readily available, and book length treatments appear regularly, though even here only a relatively small percentage of any one flora has been thoroughly studied.

However, when it comes to the tropics, that is another story. Even though many more than half of the world's 300,000 flowering plants live in the lands where winter never comes, about their floral biology much less is known. This is partly due to climatic difficulties in working in the tropics and partly because the floras are far from completely understood - and will not be so for decades to come, not to speak of insects and other animals. However, much scattered information is available, nevertheless, through the now classical works of H. G. Baker, C. H. Dodson, R. Dressler, V. and K. Grant, D. H. Janzen, H. Kugler, L. van der Pijl and S. Vogel, to name a few, and through the active research of many contemporary evolutionists-ecologists who study the taxa of their choice.

To his great credit, Professor Peter Endress of the Institute of Systematic Botany, at the University of Zurich, Switzerland, has pulled together all this literature and made it accessible to English readers in one volume. One of the world's most highly respected authorities on floral development and ecology and a prolific author over 25 years in his own right (32 of his titles are listed in the bibliography), Endress attempts a "comprehensive synthesis" of tropical floral biology and its morphological, ecological, taxonomic, and evolutionary implications. Considering the enormous lacunae in tropical biology in general and taxonomy in particular, he has in many ways succeeded beyond expectations. Part of the credit, let it be said at the onset, must go to the many hundreds of illustrations, not only drawings, but fabulous macro- and SEM photographs, for they are a glory to behold and will gladden even a mathematically-inclined ecologist's heart.

The short Introduction presents floral ecology, especially in the tropics, in an evolutionary context. Endress uses the "flamboyant" (Delonix regia, a leguminous tree with a brilliant mass of orange flowers) as an example of our need for additional research. Although this tree is widely planted throughout the tropics, "almost nothing is known about its floral biology," with the pollination as yet unstudied in its native Madagascar (where the species, long lost, was re-discovered in a forest preserve in 1932). "Thus, there are a number of very scattered bits of information, which do not give a coherent understanding of the flowering in this species. It may stand as an example for the paradoxical situation of how poorly known even 'familiar', conspicuous and widely used plants in the tropics are and how they are threatened by extinction in their natural habitat."

The bulk of the text is of two equal parts. The first (Chapterers 1-7) deals with general structural and biological features of flowers and demonstrates the incredible diversity of their morphology and function; the second part (Chapter 8) focuses on the flowers of a few selected tropical groups and emphasizes their structural and biological idiosyncrasies and evolutionary features. Thus, "Floral Organization" (Chapter 2) deals with the origin of sepals and petals (no strict definition is possible: it seems to be a matter of function leading to convergence), stamens and carpels, and the evolutionary aspects of floral phyllotaxy; "Floral Construction" (architecture, gestalt) (Chapter 3) deals with radial vs. bilateral symmetry, flag-flowers, trap flowers and the "struggle for space" within the bud; "Floral Adaptation" which looks at different pollinators (mode, style) (Chapter 4) gives us a fascinating array of co-evolutionary syndromes; "Special Differentiations of Pollinator Attractions" (Chapter 5) covers nectaries, elaiophores, perfumes, optical displays, and visual clues; "Special Differentiations Associated with Breeding Systems" (Chapter 6) deals with sex expression, heterostyly, and male/female allocation; and finally "The Process of Anthesis" (Chapter 7) focuses on structural changes during flowering, longevity, rhythmicity, the flowering within individuals and whole populations (Gentry's "Big Bang" species vs. "steady state" species), Janzen's "traplining" by "trapliners," i.e., widely dispersed individuals visited by wide-ranging pollinators, a matter now of monument importance, what with the ongoing fragmentation of tropical forests and thus the need for large preserves.

The second half of the book (Chapter 8) discusses "Floral Diversity and Evolution of Selected Systematic Groups in the Tropics." Arranged according to Cronquist's system, the examples are chosen to span the greatest diversity, from primitive to the most highly specialized, and include, for the taxonomist and floral ecologist, many fascinating discussions of various Magnoliales (e.g., in Degeneria - the carpels are not "open," as often reported!), Aristolochia and Rafflesia, Lecythidaceae, Passiflora, the legume (sub-) families, Asclepias, and the evolutionary steps that led to these bizarre flowers, and finally, in the Monocotyledons, the ginger and orchid families. The book ends with a short summary (Chapters 9 and 10) of homology vs. convergence and parallel evolution and with a plea for many additional observations in the natural habitat and a synthesis at all levels, for which this volume has certainly laid the foundations. There are taxonomic and general indices, 59 pages listing fully 1704, mostly recent, references, and a glossary.

It seems petty to criticize so monumental an effort, but a number of annoying linguistic matters have made this inevitable. First of all, the book will not win a prize for grace and clarity in writing, and Germanic (Swiss?) transliterations and awkward or imprecise use of subtly differentiated words (e.g., "explained" when he meant "exemplified") make reading it heavy going. And what is one to make of the only, and meaningless, definition of a flower which starts out Chapter 2: "Flowers are complicated plant parts."? More importantly, and perhaps because of his great grasp of the field, Endress has yielded to the temptation of creating new terms and resurrecting or redefining old discarded ones even when terms universally accepted in both botany and zoology are readily available. Thus, bilateral symmetry (zygomorphy) becomes "monosymmetry," radial symmetry (actinomorphy) becomes "polysymmetry," and subtending bract becomes "pherophyll" (but when you look up pherophyll in the glossary, it says "see subtending bract"). As we have just seen, Endress himself feels obligated more often than not to put the commonly used term in parentheses after his own unorthodoxies and on occasion even slips back to the conventional usage, as in the case of "flower" vs. "blossom," the latter defined as a "plant part that looks like a flower and functions like a flower," and may in fact even be a flower in the strict sense; thus "blossom" is redefined as anything attractive, from a flower petal to a whole inflorescence. In a further explication, " 'flower' is related to the organization, and 'blossom' to the gestalt." It is silly to reinvest time-honored English words in common use with new and specialized meanings and pointless to introduce a new set of terms unless necessary. (Cambridge University Press, where was your responsible editor when we needed you to protect a misguided author from his erudition?) By the same token, there is the constant use of "synorganization" when in most instances fusion, or union, will do; even these words are differentiated, with "fusion" used if organs of different kind join, and "union," used if organs of the same kind join. As another example, "open" will serve better than "apert" (from Latin,, meaning open), a term never used except in a Latin species description. Finally, some definitions in the glossary are incomplete (e.g., racemose), and other important ones, are missing (e.g., homeosis, homeology, determinate, indeterminate).

But no matter! This is an important book, a landmark reference that has no peers, full of facts and theories, beautifully illustrated, written by a brilliant mind, that needs to be on the bookshelf of every ecologist who wants to "understand" the flowers of the tropics, and thus help, by studying their marvelous structures and functions, to preserve this irreplaceable living legacy for future generations.

HUGH H. ILTIS UNIVERSITY OF WISCONSIN-MADISON Department of Botany 430 Lincoln Drive Madison, Wisconsin 53706-1381
COPYRIGHT 1996 Ecological Society of America
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Author:Iltis, Hugh H.
Article Type:Book Review
Date:Mar 1, 1996
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