This chapter deals with the wider context of morphological botany, to which floral diagrams are intimately connected. A definition of flowers is presented , followed by a presentation of the different floral organs and their evolution. The perianth and its homology is explained, reflecting different evolutionary trends. The floral complexity is shown through trends in the androecium and gynoecium. Different factors contributing to the diversity and evoluton of flowers are discussed, such as nectaries and hypanthia and changes in symmetry. The importance of phyllotaxis in the development of flowers is demonstrated and the difference and transitions between spirals and whorls is highlighted. Meristic changes and various fusions of the floral parts are clarified.

Floral diagrams are presented for sixty families out of fifteenorders of Supperrosidae, including the large and diverse Malvaceae and Leguminosae. The rosids evolved as a major pentamerous clade with five whorls of organs including two whorls of stamens (diplostemony). The clade shows a great amount of diversification, as an increase in complexity with a stamen increase, or a simplification linked with wind pollination through loss of petals. Flowers are generally much diverse with different elaborations of hypanthia. Besides the lower orders, two major clades malvids and fabids are presented, with a large number of families in each. The diversity of characters for different groups are highlighted and floral diagrams are used to clarify important evolutionary shifts, as in Brassicales and Malvales.

Floral diagrams show important morphological characters in an comprehensive way. This allows for comparison between different groups of plants and to recognize trends in floral evolution through specific character syndromes. Apomorphic tendencies are a clear expression of the importance of morphological characters that allow for the understanding of specific trends in flowers and the recognition of taxonomic groups. Changes in morphology are rarely abrupt, more often subtle and gradual, and this can be captured by floral diagrams.

Floral diagrams are presented for eleven families out of five orders, including Gunnerales.The early diverging eudicots represent a transitional group, sharing characters with basal angiosperms and Pentapetalae. While the basal Ranunculales show a clear diversification of flowers with new evolutionary trends, most families higher up in the phylogeny show a progressive pauperization of flowers linked with wind pollination and culminating in the Gunnerales.

Floral diagrams are presented in the context of the most recent phylogeny of the angiosperms. A pragmatic approach is presented regarding the delimitation of families. The importance of using floral diagrams in representing relationships of families including fossils is highlighted.

Floral diagrams build the foundations for the understanding and identification of flowers. The process of constructing diagrams is comparable to an architect laying the foundations of a building. It allows for the understanding of the special relationships of organs in the flower and ultimately captures the information to predict relationships with pollinators and occurring evolutionary trends. It is not always an easy task to capture floral diversity by floral diagrams. To be fully comprehensive, several volumes would have to be written, comprising several hundred detailed drawings. Flowers represent dynamic entities prone to influences of the environment, interactions with pollinators, pressures during floral development and genetic shifts. How a flower looks at maturity is largely caused by the processes affecting the floral development, with subtle shifts in time and space causing major changes in the floral morphology (discussed in Ronse De Craene, 2018, 2021). These changes allow us to predict trends in the floral evolution and reflect the apomorphic tendencies found in different clades. However, certain characters on floral diagrams are conservative so as to reflect where a taxon belongs and can be used for identification at least to family level.

The major symbols used in this book are presented and highlighted, as well as a representation of a floral diagram in the context of its surroundings. This chapter is an important reference for understanding and interpreting the diagrams in this book.

The significance of the use of floral diagrams is discussed in this chapter, including different types as well as its advantages and limitations. Floral diagrams can catch the diversity of flowers, including accessory structures and floral heteromorphism. The importance of floral development, the drive of pollination and evolutionary developmental genetics is shown in the shaping of floral structures and as a reflection of floral evolution.

Floral diagrams are presented for fourteen families out of six orders of the basal groups of angiosperms. The floral diagrams of the basal angiosperms illustrate the early progression of flower diversification. Starting with the most basal angiosperms, different trends in flower evolution are shown through diagrams, illustrating the transition of spiral to whorled trimerous flowers, incipient transformations of floral organs and accessory structures, and the progressive fusion of organs. The major orders are presented with representatives of the most important families and their trends, including Laurales, Magnoliales and Piperales.

Floral diagrams are presented for twenty-eight families out of ten orders of monocots, covering the diversity and evolutionary trends within this largely homogeneous group. The monocots are basically defined by their trimerous Bauplan, regulating the structure of the flower as well as its evolution. The basalmost orders demonstrate greater variation with higher or lower stamen numbers, while higher groups have evolved within the constraint of a pentacyclic arrangement that has changed very little. Variations in flower morphology as adaptations to different pollination systems are regulated by hypanthial growth, reductions of organs or stamen increases, and monosymmetry.