Horticulture has remained far behind in understanding of botanical principles. Recent phylogenetic (DNA-based) reorganization of higher plants has revolutionized taxonomic treatments of all biological entities, even when morphology does not completely agree with their organization. This book is an example of applying principals of botanical phylogenetic taxonomy to assemble genera, species, and cultivars of 200 vascular plant families of ferns, gymnosperms, and angiosperms that are cultivated for enhancement of human living space; homes, gardens, and parks. The emphases are on cultivated species but examples of some plants are often shown in the wild and in landscapes. In providing descriptions, it is assumed that students and other interested individuals have no background in general botany (plant characteristics), or nomenclature. Fundamental features of all plant groups discussed are fully illustrated by original watercolor drawings or photographs. Discussion of the families is grounded on recent botanical phylogenetic treatments, which is based on common ancestry (monophyly). Of course, phylogenetic taxonomy is not a new concept, and was originally based on morphological characteristics; it is the DNA-based phylogeny that has revolutionized modern biological classifications. In practical terms, this book represents the horticultural treatment that corresponds to phylogenetic-based botanical taxonomy, to which is added cultigens and cultivated genera and species. Hence, the harmony between horticultural and botanical taxonomy.