Travel to your nearest nature reserve. It could be anywhere, within a human habitation or wildland, on continents or islands around the globe. It could be a forest, shrubland, grassland, forbland, or even desert. Across your view is a diverse array of plants, complete with a complex architecture with several levels from the ground surface to the highest leaf, be it a redwood tree extending hundreds of meters into the sky, or a diminutive, but still complex, structure only 10 cm high of mosses, liverworts, and cryptogams. As you separate the stems and look down, you see roots: tens of meters of roots or rhizoids for every square meter of the soil surface. Take your hand lens and pull up some of those roots. There will be soil hanging from those roots, held together by tens to hundreds of meters of threads of fungal hyphae per cubic centimeter. The vast majority of these hyphae form mycelia from many species of fungi, directly connecting fine roots to the larger soil matrix, serving as a living pathway interconnecting the plant, which is actively fixing carbon, within the micro patches of nutrients and water necessary to fix that carbon.

From the beginning of mycorrhizal research, understanding of functioning was based on the morphological structure of the plant–fungus interface. The structure of the fungal hyphae within the root, which regulates the exchange of resources between plant and fungus, and the extramatrical hyphae, the extent and locations of which dictate the ultimate flows of resources between soil, hyphae, and root, characterizes a mycorrhiza, determines the type of mycorrhiza, and, to a large extent, determines the functioning of that mycorrhiza (255). Overall, knowing these two structural components, internal root colonization and extramatrical hyphae, allows us to make a number of predictions about the mechanisms and quantity of resource exchange between the two symbionts.

During the nineteenth century, the Selkirk Settlement of Canada and the Homestead Act in the United States led to some of the most dramatic and widespread destruction of native ecosystems across a short time period in history. Soils across the Great Plains, from the Mississippi River to the Rocky Mountains, from the Chihuahuan desert of Mexico to the Boreal Forests of Canada, an area of around 4 million kilometers squared, were nearly all turned over for agriculture, from prairies with dense grasslands to riparian regions with extensive forest cover and deep roots, within the decades from approximately 1820 to 1890. By the 1890s, a protracted drought led to a collapse of agriculture in the United States, Canada, the Ukraine (the Selk’nam genocide), and elsewhere. The young field of ecology was just beginning, documenting the community ecology of recovery at lakeshores (182), glaciers (175), and from the abandonment of highly disturbed agricultural lands (170).

Wildlands continue to decline globally at a rapid rate. As hunter-gatherers, the human population probably approached a global K value, estimated at 8.6 million, approximately 10,000 years ago, and continues to grow, from 2.5 billion when I was born, to rapidly approaching 8 billion as I write (65). Deforestation rates are in the range of 10 million hectares annually. Atmospheric CO2 is rapidly increasing and growing-season days are projected to move as much as 10° poleward higher in latitude over the next three decades (407). In the environmental media, the idea of re-wilding (reintroducing absent or declining species into relatively intact habitat) has been gaining strength as the likelihood of mass extinction materializes.

Mycorrhizal fungi are a critical linkage between the soil, containing water and inorganic and organic nutrients, and the plant itself, the photosynthetic unit that converts solar energy to complex C compounds upon which the terrestrial world depends. Sir Arthur G. Tansley (696) first defined the term ecosystem, noting that organisms cannot be separated from their environment, thereby forming a biological–chemical–physical system, or an ecosystem within a relatively stable but dynamic equilibrium. This, the origin of the term ecosystem, breaks down Clements’ concept of biome, where climate is the overriding regulator of the community, into a view of the multiplicity of interacting biotic, chemical, and physical components that allow for the existence of life.

Now travel back to your nearest nature reserve, but simultaneously look at the adjacent agriculture field or human urban neighborhood. Instead of just looking at what you can readily see, the diverse array of plants and animals; the complex architecture and the smells of the flowers and the diverse array of shapes and colors, double that, or maybe even increase it 10-fold by imagining that it is connected to what you cannot see belowground! Diverse plant and fungal compositions and structures are interconnected through multiple networks transferring resources and chemical signals. They may persist for only a day or even a few minutes, but alternatively maybe for decades, or even centuries. Even observing that part of the ecosystem, whether through minirhizotrons and ground-penetrating radar, or sampling and microscopy, you will only visualize a tiny fragment of that world. In the world of mycorrhizae, imagination may be the single most useful tool!

Mycorrhizal symbioses have existed since at least the Ordovician period, between 400 and 500 MYa. Associations, and even some plant–fungus species pairs, have existed in morphologically recognized combinations through every climate and substrate condition throughout that time period. Across that vast time, virtually every potential condition likely would have been encountered. Over the past eight chapters, I have covered nearly the entire range of conditions that mycorrhizal relationships have encountered: some ancient, some novel.

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.