American Journal of Botany 91 10 1683 1699 2004 FOSSILS AND PLANT PHYLOGENY1 PETER R CRANE 2 5 PATRICK HERENDEEN 3 AND ELSE MARIE FRIIS4 Royal Botanic Gardens Kew Richmond Surrey TW9 3AB UK 3Department of Biological Sciences The George Washington University Washington DC 20052 USA 4Department of Palaeobotany Swedish Museum of Natural History Box 50007 S 104 05 Stockholm Sweden 2 Developing a detailed estimate of plant phylogeny is the key first step toward a more sophisticated and particularized understanding of plant evolution At many levels in the hierarchy of plant life it will be impossible to develop an adequate understanding of plant phylogeny without taking into account the additional diversity provided by fossil plants This is especially the case for relatively deep divergences among extant lineages that have a long evolutionary history and in which much of the relevant diversity has been lost by extinction In such circumstances attempts to integrate data and interpretations from extant and fossil plants stand the best chance of success For this to be possible what will be required is meticulous and thorough descriptions of fossil material thoughtful and rigorous analysis of characters and careful comparison of extant and fossil taxa as a basis for determining their systematic relationships Key words angiosperms fossils paleobotany phylogeny spermatophytes tracheophytes Most biological processes such as reproduction or growth and development can only be studied directly or manipulated experimentally using living organisms Nevertheless much of what we have inferred about the large scale processes of plant evolution and much of what we know about the plant diversity to which those processes gave rise is based on preserved samples taken from living organisms These samples brought together in the collections of museums and herbaria around the world are crucial to attempts to name characterize systematize and understand the origin of the variety of plant life They are also the starting point for any investigation of plant phylogeny Preserved specimens are the essential samples and indispensable reference points on which knowledge of botanical diversity and large scale processes of plant evolution are based Fossils like herbarium specimens and leaf fragments kept in silica gel for DNA analysis are the remains of once living organisms gathered at a particular time and from a particular place There is no essential difference between a dried specimen collected a decade ago and a fossil specimen entombed within rocks for millions of years Neither is a perfect sample of a complex living organism but combined with knowledge from other samples of plant diversity and supplemented by information from living plants both can help answer questions about the form of the botanical tree of life and the processes by which it has come about Even relatively recently paleontological data have been considered by some e g Hughes 1976 1994 to be the final arbiters in any effort to understand plant phylogeny We do not subscribe to this view Recent advances in systematic theory have developed a more sophisticated perspective and have helped to clarify exactly what information fossils can and cannot deliver e g Hill and Crane 1982 Crane and Hill 1987 Patterson 1981 Doyle and Donoghue 1987 Gauthier et al 1988 Donoghue et al 1989 The result is a straightforward and uncompromising view of paleontological data In a claManuscript received 21 January 2004 revision accepted 17 June 2004 The authors thank Jeffrey A Palmer Douglas E Soltis and Mark W Chase for the invitation to contribute to this special issue and James A Doyle for his valuable comments on the manuscript Many of these issues have been discussed during meetings of the Deep Time Research Coordination Network NSF grant RCN 0090283 5 E mail p crane rbgkew org uk 1 distic context neither fossils nor their stratigraphic position have any special role in inferring phylogeny and although more complex models have been developed see Fisher 1994 Huelsenbeck 1994 these have not been widely adopted But fossils do provide additional information on the diversity of plants which must be accounted for by any comprehensive understanding of plant phylogeny and evolution e g Doyle and Donoghue 1987 They also provide evidence on the timing of evolutionary events that is useful to develop and test ideas on how the variety of plant life may have arisen e g Doyle and Donoghue 1993 Crane et al 1995 In this paper we discuss the contributions of paleobotanical data to understanding large scale evolutionary patterns in the plant kingdom We begin with a brief consideration of the nature of the paleobotanical record and the temporal information it provides We then review three key areas of plant phylogeny with a particular focus on the contributions of paleobotanical data the origin and diversification of vascular plants the origin and diversification of seed plants and the origin and diversification of flowering plants The many other contributions of paleobotanical data to areas of science as diverse as global environmental change biostratigraphy and paleogeography are not considered in this paper FOSSIL PLANTS AND CHARACTERS FOR PHYLOGENETIC ANALYSIS Fossil plants are generally more poorly known than their living counterparts However perhaps surprisingly they are sometimes exquisitely well preserved In many cases they provide a level of structural detail that cannot be retrieved from living plants without significant investment of time and effort For example permineralized plant fossils from classic localities such as the Eocene Princeton Chert preserve nearperfect anatomical details of stems fruits and seeds e g Cevallos Ferriz and Stockey 1991 Pigg and Stockey 1996 Stockey et al 1998 Equivalent information for the extant relatives of these plants is frequently not readily available Similarly the quality of preservation of morphological and anatomical details in charcoalified flowers from Cretaceous fossil floras may exceed that seen in standard herbarium specimens e g Friis 1990 Herendeen et al 1994 1995 Keller et al 1996 Magallo n Puebla et al 1997 2001 Scho nenber 1683 1684 AMERICAN JOURNAL ger et al 2001 Friis et al 2003b In both these cases detailed comparison of fossil and extant material often requires extensive morphological and anatomical surveys of different organs from living plants These and many other examples show that frequently it is not the quality of
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