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.

The Pentapetalae have diversified very rapidly, leading to two major successful clades, the superrosidae and superasteridae. Although it is still uncertain how the Pentapetalae diverged from ancestral flowers, their regular floral pentacyclic and pentamerous Bauplan is almost unversal and firmly established in all evolutionary lines. The possibility is presented that intermediates such as Berberidopsis regulate the transition from a spiral to a pentamerous pentacyclic flower. The diversity and unique evolutionary trends of early diverging orders with unclear affinity, Dilleniales and Santalales, are presented.

Floral diagrams are presented for thirty-six families out of nine orders of SupperAsteridae. Asterids represent the pinacle in Pentapetalae floral evolution, expressing a strong synorganization between whorls and the stabilization of a tetracyclic Bauplan with five sepals, five petals, a single whorl of stamens (haplostemony) and two carpels. The lower Asterids share characters of basal Pentapetalae and rosids and present all characteristics of a transition to euasterids. Diferent trends are higlighted in lamiids and campanulids. The development of a stamen-petal tube emerges in the basal Asterids and is prominent in the lamiids in association with median monosymmetry. An important evolutionary trend representing the sterilisation of stamens in Lamiales is shown through floral diagrams. In Campanulids there is a shift towards the reduction of the stamen-petal tube as well as the reduction of the calyx linked with an inferior ovary and a lower number of ovules.

This chapter represents a summary of the major taxonomic groups and their floral evolution. The value of floral diagrams is highlighted as a means to stress similarities and differences between the major angiosperm groups.

Floral diagrams are presented for twenty-one families of the highly diverse orders caryophyllales and polygonales. The caryophyllids represent a small but important clade close to the asterids. The flowers show important evolutionary trends linked with a progressive loss of petals, and their reinvention of petal-like structures in derived groups, such as coloured sepals or staminodes. Stamen evolution also shows unique trends linked with spatial constraints and secondary multiplications. The ovary shows a general tendency to the development of central placentas and the reduction in the number of ovules. Floral diagrams are used to illustrate the major evolutionary trends within caryophyllales and specifically within the diverse family Polygonaceae, in addition to specific diagrams representative of families.

The algae are oxygen-producing, mainly aquatic organisms possessing enormous morphological, cytological, molecular and reproductive diversity. Modern studies have led to the recognition that algae represent a number of evolutionary lines or lineages, almost all of which are represented in the British freshwater flora. Most of these lineages probably arose independently as a result of endosymbiosis. There has been a tendency by protozoologists to adopt what has been termed a ‘protistan’ view and to place these lineages into the Protista, a kingdom that itself is unnatural (Corliss, 1994). The majority of the lineages are eukaryotic, in which the cells have a double membrane surrounding the nucleus and most other organelles such as chloroplasts. Another evolutionary line, the Cyanobacteria (Cyanophyta or blue-green algae) are often considered together with other algae, although these organisms are prokaryotic (membrane-bound organelles absent) and more closely related to the bacteria.

A few algae have photosynthetic structures known as cyanelles, which in many ways are intermediate between a chloroplast and a free-living bluegreen alga. In most such cases, the rest of the cell resembles quite closely other species of algae with normal chloroplasts. It is likely that the cyanelles have evolved relatively recently from free-living cyanobacteria. However, in the case of Glaucocystis nostochinearum, which has conspicuous cyanelles, there is still doubt about its relationships and it is here classified in its own phylum, the Glaucophyta. Some other organisms possess no photosynthetic structure, but are otherwise quite similar to those that have chloroplasts. These are often treated as protozoans, but clearly belong in the same phyla as the related photosynthetic organisms. Most examples are in the flagellated phyla (Euglenophyta, Cryptophyta, Dinophyta and Chrysophyta). The first three, but not the Chrysophyta, are nowincluded in this edition.

What constitutes an algal species has been the subject of much debate (see John and Maggs, 1997, for a review). Most species are recognized by discontinuities in sets of morphological characters observed with the light microscope, so that algal systematics is largely based on what has been termed ‘the morphospecies concept’. Culture studies have frequently shown that species concepts based solely on characters observed in field-collected material are often too narrow and the taxonomic validity of many of the characters used is open to question (see Trainor, 1998, and his comments in a review of the genus Scenedesmus sensu lato).