Any selection of the most important decorative plants in the gardens of Europe and North America will unavoidably be subjective. The topic is vast, and it is made much more complex by the dominance, in many genera, of variants selected or bred for their horticulturally desirable propertiescultivars-that are often of complex hybrid origin. Whereas elsewhere in this book individual species are discussed, that approach is scarcely possible under this heading. No one could deny roses a place, for example, but it would be unrealistic to pick out a single cultivar as representative of the entire genus; although many of the species are cultivated, they have a much less prominent place in gardens than the cultivars. It is the important role of certain of the species in the ancestry of the cultivars that underpins the whole subject.