The seed of this book was actually a mere private survey of current angiosperm phylogeny and taxonomy containing lists of the features characterizing the different clades. At first, that seed was not intended to grow into a publication, neither at the world-wide web nor as a printed book. Nevertheless, it constantly expanded and, after having been offered a potential website by Professor Birgitta Bremer at the Hortus Bergianus (the Bergian Botanical Garden) in Stockholm, I decided to further extend the text and make it readable for other people than myself. Hopefully, the book may be used by any educated person interested in advanced angiosperm systematics. However, it is not designated for beginners. Nevertheless, the book is provided with glossaries and these should facilitate even for non-specialists the understanding of the text.
The book may also be looked upon as a part of the digital Tree of Life (in Swedish ‘Livets Träd’), which was put together by me and Ronny Larsson, professor of systematic zoology at the University of Lund, and made available to the public in 2006. The Tree of Life covers all known major lineages of organisms, although the chapter dealing with flowering plants was abbreviated at that time.
The present book, The Phylogeny of Angiosperms, represents a first preliminary version, certainly suffering from an enormous amount of errors and other deficiencies. Hence, I would be grateful to the readers for all comments and suggestions of improvements. Any opinions about the contents can be forwarded directly to the author’s e-mail address: . The presentations of the taxa are especially in need of additions and corrections. One of the most important aims of this book is to provoke scientists to intensify the research on the numerous poorly known clades. For this purpose, I have attached a list of missing characters for the taxonomic groups treated in this book.
Angiosperm systematics has undergone an entire revolution during the last twenty years. This enormous progress is mainly due to the advancement of molecular approaches, computer technology and cladistics theory. The recent renaissance of plant morphology has also provided an increasing amount of new data. Phylogenetic analyses of nearly all main lineages of flowering plants have been carried out at an accelerating speed. If this effort continues, utilizing ever more nuclear genes in particular, the Angiosperm Tree of Life will hopefully be almost completely covered within the next few decades, at least when speaking of the chief lineages of extant flowering plants. The main branches of this phylogeny now seem to be clarified, new analyses more or less confirming and solidifying most of the cladistic hypotheses suggested during the last fifteen years. Yet an enormous amount of genera are not or only poorly investigated.
During my career as a biological systematist the views on flowering plant systematics and evolution have fundamentally changed more than ever before. Hence, it has been and still is an extremely fascinating period for an evolutionary biologist. At the same time, we become more and more aware of the fast growing threats against Earth’s biodiversity and that future generations will probably not be able to enjoy the incredible multiplicity of species that surround us today. Often, the threat is most severe against such taxa which are critical for our understanding of the phylogenetic patterns and, consequently, for the evolutionary processes. Species-poor lineages with very limited distributions are often sister-groups to species-rich clades with considerable genetic diversity. Such old yet tiny lineages are crucial for character polarization and our understanding of the evolutionary processes of their large sister-clades. Examples are Amborella trichopoda (sister to all other angiosperms), Petrosaviaceae (sister to the chief clade of monocotyledons), Gunneraceae (sister to Pentapetalae), Pennantia (sister to all other Araliales), Tepuianthus (sister to the remaining Thymelaeaceae), and the tiny lineages within Staphyleales (a basal clade among Malvanae).
During the childhood of molecular phylogenetics approaches emphasized – often solely – on DNA and neglected morphology, etc. Fortunately, researchers have subsequently become aware of the importance of ‘total evidence’ analyses, combining morphology (i.a. Stuessy & al. 2003), cytology (e.g. Levin 2002) and molecular features.
We have come to a point where comprehensive and even detailed surveys of the current state of knowledge may be produced. This book is such a synthesis of current information, both retrospective and forward-looking.
Results from systematic-phylogenetic research are overflowing at an increasing rate. This means that a traditional paper-book that tries to be highly updated will become hopelessly outdated already at the moment of printing. Digital publication is a simple solution of such a problem. Any change in the text may be made quickly, as soon as new information is available. The book is as easily accessible as any web-carried data. Moreover, it is a low-cost alternative – free to use.
Among all those sources that I have utilized for compiling the information in this book, I will here mention only a few of the many outstanding references: Kubitzki & al. (1993 onwards) The Families and Genera of Vascular Plants; Nickrent (1998 onwards) The Parasitic Plants Website; Stevens & al. (2001 onwards) The Angiosperm Phylogeny Website; and – for the nomenclature of suprageneric names – the websites and articles by Dr James Reveal (the University of Maryland).
Many clades are very difficult to define using morphological features. This is due to the extensive degree of homoplasy found among angiosperms. These clades are nevertheless recognized as monophyletic in most cladistic analyses and thus have to be accepted, even if they cannot be identified in the field using traditional approaches. Some well-known examples are Celastraceae, Lamiaceae, Plantaginaceae, Ranunculaceae, Ruscaceae, Salicaceae, and Scrophulariaceae. Homoplasies are rules rather than exceptions among angiosperms. All types of characters – even molecular characters – are subject to parallelisms and reversals. Some genes coding for anatomical, phytochemical or other features may be switched off rather than simply lost, which means that they may be easily reacquired over and over again.
Information on species number of the groups is often very approximate and uncertain, and, of course, depends on the divergent views on species definitions and generic delimitations among different taxonomists. As an example, some authors may have a very wide species concept, whereas others may prefer a restricted concept. As a result, the number of species within the genus in question may vary between ten and more than fifty. However, such differences of opinions will certainly always exist.
The present book is subdivided into:
• An introduction to the angiosperm phylogeny and taxonomy used in this book. This chapter is named Magnoliopsida.
• Chapters describing all major clades of angiosperms.
• An alphabetical list of accepted generic names and their synonyms.
• Two different glossaries: one general glossary explaining morphological, cytological, anatomical, embryological and other terms; and a second glossary dealing with phytochemical terminology.
• Finally, I have also included lists of unknown character states for the different clades in alphabetical order. According to my opinion, this is not the least important part of the book. A goal of utmost importance is to present what we do notknow. Some character complexes, such as embryology and ultrastructural features, are particularly poorly studied for numerous taxa. Many character states are unknown for critical taxa such as Amborella. I have already mentioned the importance of having sufficient knowledge of the crucial sister-groups of larger lineages, since these are critical for our understanding of phylogeny and character polarization. In general, polarization is very difficult and often impossible for angiosperms, since their relationship to other seed plants remains obscur.
I have deliberately left out some types of information:
• Information about the hypothetical ages of clades and nodes are excluded, since these are still very unreliable and depend on our knowledge of the phylogeny in question and the different methods of age determination used. In too many cases there may be substantially disparate estimates of the age of a specific clade. The issue is also intensively debated. In particular, the constrained (fossil-based) ages are usually much younger than the relaxed ages. Moreover, the identification of (often fragmentary) fossils is usually more or less uncertain.
• Literature references will only exceptionally be found within the text. Instead, a list of literature is given at the end of each main section. It is my hope that the reader will find the text somewhat easier to follow, instead of finding extensive lists of references packed in the middle of the sentences. General references, dealing with a larger part of the angiosperm system, are found within the chapter Magnoliopsida.
• Information on branch support, sequenced genes and cladistic algorithms are not presented in the phylogenetic trees in this book. Such important data are given in the original publications; references to these will be found in the literature lists.
• Historical sections or comparisons with previous views and ideas are not included here. Such information may be found in almost all other textbooks of plant systematics and my opinion is that providing such a chapter here would not add any new knowledge beyond those already published and comparatively accessible to the reader.
• Sections on methodology or cladistic theory are beyond the scope of this book. Excellent descriptions of different technical approaches and phylogenetic theories are provided in numerous publications.
• Drawings (other than phylogenetic trees) are not included in the first version of this book. Instead, a large and growing number of colour photos are provided.
In this preface I will also take the opportunity to explain some of those principles that have been the guidelines in my present account of the flowering plants.
The first and foremost aim is to present a phylogenetic system covering all main clades of flowering plants and only accepting monophyletic groups.
Ranks in the traditional sense (i.a. family, suborder, order, and subclass) are not used in this book. Instead, the concept of “rank” is used only in reference to clades. In other words, the subdivision of a group exclusively follows the sequence of branches in a phylogenetic tree. According to the Article 3.1of the Phylocode, the nomenclature is independent of categorical rank. A phylogenetic rank is unimportant for the formal naming and should not influence the spelling of the name of the group. Another principle that I have tried to follow is the one stated in the Article 3.2, namely that synonymy, homonymy and precedence are independent of categorical rank. Finally, I have not followed the traditional nomenclatural system of rank-dependent suffixes on the clade names, since this would soon result in a hopelessly large amount of different suffixes. In traditional systematics using traditional ranks, this would mean that one has to change the suffix (often the name as well) as soon as the clade becomes less alternatively more inclusive.
The reader will soon discover that I have promoted a more narrow “family” concept (I apologize for here using this specified rank according to the custom of a more traditional taxonomy) than, e.g., the now generally accepted system of APG III (2009). Iridales (Asparagalesof APG), for instance, are here divided into 28 subclades (“families”). Instead, I have followed the principle of “too much is better than too little” in presenting the information.
All clade names should follow the principles of priority. This is actually stated in article 16B.1 of the International Code of Botanical Nomenclature: “In choosing among typified names for a taxon above the rank of family, authors should generally follow the principle of priority.” Unfortunately, this recommendation is usually not followed for suprafamilial ranks in the traditional taxonomy.
The selection of cladograms and summary trees is, of course, very subjective. Yet I have tried to choose the latest available phylogenetic trees founded on as many taxa and characters (usually only molecular data) as possible, and consisting of reasonably supported clades. In many cases, I have simplified the cladograms in order to make them handier for the reader, although trying not to exclude more than a minimum amount of information. If an original cladogram is too large for a single page, I have partitioned it into two or more pages.
A classification should follow the prevailing and generally accepted phylogenies as closely as possible. Moreover, a classification should be
• universally applicable
If following the phylogenies as closely as possible, these rules will be complied with.
I express my special gratitude to the staff at the Hortus Bergianus (the Bergian Botanical Garden) at the University of Stockholm for putting a website at my disposal. A laborious task was – and still is – spent by Dr Niklas Wikström (Hortus Bergianus, Stockholm) in creating and administrating this site.
I am particularly indebted to Dr Peter F. Stevens at the Missouri Botanical Garden and the University of Missouri at St Louis, whose tremendous and invaluable Angiosperm Phylogeny Website has been one of the most important sources of information. This formidable website will be repeatedly cited in the text.
But first and foremost I am grateful to all those indefatigable and often self-sacrificing botanists, collectors and amateurs of all times who have devoted their lives to the noble aims of gathering plants and data. Thank you!
This book is dedicated
to the memory of my late friends
Rolf and Gertrud Dahlgren