Earlier chapters have been designed to serve particular purposes. Chapter 3 provides a connected overview of the concepts underlying our current understanding of the long history of plant evolution. Chapter 4 reveals that while on a geological time scale, humankind arrived on the scene relatively recently, human impacts on the Earth's ecosystems have been very dramatic and are destined to increase. Examples of the effects of human activities on ecosystems are all around us, and it could be claimed that such interactions are so obvious they hardly need to be documented. However, as we have seen above, evidence suggests that the cumulative impact of human activities on the biosphere, both directly and at a distance, have often been underestimated. Also, the full complexity of the interactions of plants and humans is becoming evident, resulting in the recognition of many different categories. For the convenience of devising helpful groups, a species may often be classified in different categories according to the circumstances (Chapter 6).

In total, there have been many thousands of published papers of different facets of plant evolution. Some have investigated the early evolution of plants and animals, others have examined the patterns and processes that have generated, through time, the millions of species that live on Earth.