Flowers have a universal appeal that makes them a perennial theme in studies of plant biology. Their enigmatic evolutionary origin and rapid early diversification have remained popular topics for scientific debate since Darwin pondered his famous ‘abominable mystery’ of the evolutionary origin of flowering plants. A major factor at the root of the problem is the vast number of ancient extinctions, both among the early angiosperm lineages and their closest seed plant relatives. Coupled with the disproportionately high diversity of the relictual extant early angiosperm lineages, their relative paucity makes it problematic to draw evolutionary conclusions using direct morphological comparisons. Among other seed plants, the three extant genera of Gnetales ostensibly most closely resemble the angiosperms in many respects, including the possession of flower-like structures that are largely insect-pollinated. Thus, angiosperms and Gnetales are collectively termed anthophytes (flower-bearing plants). Yet many (though not all) molecular phylogenetic analyses associate Gnetales more closely with conifers than with angiosperms, so their relationships remain controversial (Bateman et al., 2006; Mathews, 2009; Rudall, 2012).
Inevitably, this morphological–molecular conflict has clouded our (already imperfect) understanding of the evolutionary origin of the flower. With the possible exception of Gnetales, all of the seed plant groups that are considered most closely related to flowering plants, notably the Bennettitales, Caytoniales, Czekanowskiales, Erdtmannithecales, Glossopteridales and Pentoxylales, are extinct and known only from fossils. A recent morphological study by Friis et al. (2007) controversially identified an anthophyte clade consisting of three orders of plants with shared distinctive seed morphology: Bennettitales, Erdtmannithecales and Gnetales (the BEG group).
Thus, fossils represent an important aspect of the debate, and excellent fossil reconstructions – aided by improved and improving imaging technology – are essential to help resolve this perennially difficult issue. The authors of this book combine immense relevant knowledge of fossil angiosperms and gymnosperms; each of them has published extensively on palaeobotanical topics for several decades. Their major new textbook presents detailed accounts of many significant fossils that are otherwise poorly known or only recently discovered. They usefully review some of the contrasting hypotheses of relationships of angiosperms with other seed plants and discuss their implications for elucidating possible avenues of flower evolution from the cone-like structures that are associated with extant gymnosperms.
The book contains 20 chapters of dense text, copiously illustrated throughout with colour photographs, graphs, diagrams and drawings. An introductory chapter (chapter 1) sets up the background to flower structure and the characteristic features of angiosperms. It includes brief historical summaries of several issues that are covered in greater detail in subsequent chapters: angiosperm and seed plant phylogenetics are dealt with in chapters 5 and 6, and concepts of flower origins, specifically the Euanthial and Pseudanthial theories, are covered more comprehensively in Chapter 6. Chapters 2 and 3 outline the nature of the fossil record and provide an environmental context for the critical periods of early angiosperm evolution, especially the Cretaceous, when most early diversification took place. Chapter 4 enjoyably summarizes the places and conditions where the best early angiosperm fossils are found. Not surprisingly, the authors have their own favourite collecting sites that have yielded significant fossils; for example, western Portugal includes a wide range of remarkable sites that span the early and late Cretaceous. Chapters 7–15 review the fossils that are assigned to the extant lineages of flowering plants, focussing especially on early-divergent lineages such as Nymphaeales and Austrobaileyales, but also covering in turn the various orders of magnoliids, monocots and eudicots. Chapters 16–18 review structural diversification and pollination biology. Finally, chapters 19 and 20 present overviews of the ecological context of angiosperm diversity.
This long-awaited book represents not only a remarkable tour de force of palaeobotanical literature, but also a potentially enduring biological textbook. Part of its appeal lies in the excellence of its production. Numerous black-and-white line drawings of flowers and pollen grains of both fossil and extant plants, beautifully executed by Polyanna von Knorring, add considerably to its informative content and high visual impact.