More than 12,000 labeled plants of approximately 2,500 types are growing in the Arboretum’s living collection. These include representatives of the temperate floras of North America, Asia, and Europe. This historic collection traces its foundation to John Morris’s interest in plants from around the world, and includes plants collected in China by E.H. Wilson at the turn of the century. Many of the Delaware Valley’s "trees-of-record" (the largest of their kind) are found in the Arboretum. Most notable are the katsura, Engler beech, Bender oak, and trident maple.
Staff members have regularly engaged in plant collecting expeditions in Asia and the United States, increasing the diversity of plants available for today’s urban and community landscapes. Currently plants from 34 countries are represented in the collection with a primary focus on Asian temperate species. Significant plant groups in the Arboretum’s collection include maples, magnolia species, native azaleas, members of the witch hazel family, roses, hollies, and conifers.