Its rich and diverse collection contains representatives of more than 300 plant families of Mediterranean climates.
The Arboretum maintains collections of rare and threatened plants of unusual scientific interest. Particular specialties are world conifers, primitive angiosperms, and bulb-forming plant families.
Many of the species in these collections are not otherwise available for study in American botanical gardens and arboreta.
The Arboretum's activities in importing, selecting, and breeding choice ornamental plants, many of which are drought tolerant and pest resistant, is of great service to the public and the nursery industry. To date, the Arboretum is the original importer of more than 1,500 different selections of choice ornamentals. For examples, see the Arboretum's Koala Blooms and Rare Plant Sponsorship Programs.