Previous versions of this classic work appeared in 1948 and 1974 and treated, respectively, over 420 species in 140 genera versus about 800 species, varieties, and subspecies in 188 genera. The 2008 revision expanded to include nearly 1300 taxa in 236 genera. Most additions are either tropical species grown in Puerto Rico and the Virgin Islands, Hawaii, and the Pacific territories or native species that have increased in value for wildlife or environmental plantings in recent years. Many of the latter are shrubs from the western United States
Illustrations from the 1974 edition were reused for the 2008 edition. For new species, efforts were made to collect specimens for new photographs that are similar in style and background to those of the 1974 Handbook, but sometimes line drawings from other works had to be used. The six-page glossary was updated and expanded.