Level IV

The Arboretum, University of Guelph, is located in Guelph, Ontario, Canada, about an hour’s drive northwest of Toronto. Established in 1970, The Arboretum comprises over 400 acres of tree and shrub collections, gardens, walking trails, natural woodlands, wetlands and meadows, and is adjacent to the main university campus.

The Arboretum is home to more than 1850 different taxa of woody plants, organized into collections that include a synoptic World of Trees collection as well as a Native Trees of Ontario collection and noteworthy collections of Oaks and Beeches, Maples, Conifers  and Dwarf Conifers.

With a mandate to support teaching, research and outreach at the university, The Arboretum is integral to many undergraduate courses and acts as a ‘living laboratory’, providing support, expertise and a wide variety of plant species and environments for researchers at all levels. We also offer dozens of workshops each year aimed at the general public, and design and display interpretive signage and other materials to help connect people with plants and nature.

Set on 166 acres at the outer edge of Philadelphia's Chestnut Hill neighborhood, the Morris Arboretum & Gardens of the University of Pennsylvania Founded in 1887 as the private estate of siblings John and Lydia T. Morris. The arboretum was established in 1932 as a university-administered arboretum and public garden for research, education and horticultural display. It became the official Arboretum of the Commonwealth in 1988.

Today, the Morris Arboretum treats visitors to an ever-changing display of rare and beautiful plants and trees, all year long. It is a place of big trees, a place of beauty, a historic landscape, a scientific institution, a teaching garden, a place of art and architecture, and a place of peace and healing. At the arboretum, one discovers teaching, horticultural display, conservation and research.

The Morris Arboretum's collection of scientifically documented plants began in the late 1800's. More than 12,000 labeled plants of over 2,500 types from the temperate areas of North America, Asia, Africa, and Europe make its living collection. Some of these were collected by Arboretum founders, John and Lydia Morris, from their travels around the world. Plants collected in China by E.H. Wilson in the later 1800's and early 1900s form the foundation of the historic Asian collection. Significant plant collections include conifers, hollies, magnolia, oaks, maples, roses, flowering cherries, and witchhazels.

In 1906, industrialist Pierre S. du Pont (1870-1954) purchased a small farm near Kennett Square, PA, to save a collection of historic trees from being sold for lumber. Today, Longwood Gardens is a renowned horticultural destination, spanning 1,100 acres of captivating gardens, woodlands, meadows, and fountains, complemented by a 10,010-pipe Aeolian organ and grand conservatories. The extensive tree and woody plant collections, including rare and historically significant specimens, are internationally recognized through our Level IV ArbNet accreditation. Notably, their collection of Peirce's Trees is an American Public Gardens Association Plant Collections Network certified collection, and features trees that were cultivated in the Philadelphia region during the 19th century. In 2024, Longwood Gardens expanded its conservation efforts with the acquisition of the 505-acre Longwood at Granogue, a cultural landscape in nearby Wilmington, Delaware. Longwood Gardens remains the living legacy of Pierre S. du Pont, dedicated to bringing joy and inspiration to everyone through the beauty of nature, conservation, and learning.

The Pretoria National Botanical Garden (PNBG) Arboretum is a living showcase of South Africa’s incredible tree diversity, bringing together conservation, education, and research in a truly special way. Home to an impressive collection of indigenous trees, the arboretum plays a key role in preserving rare and significant species while offering visitors a chance to experience the beauty and importance of our natural heritage up close. One of its most remarkable features is the Baobab tree (Adansonia digitata), an iconic symbol of African landscapes known for its massive trunk and legendary resilience. Another highlight is the stunning avenue of Bolusanthus speciosus, or Tree Wisterias, which greet visitors with their graceful form and striking purple flowers. The arboretum also protects naturally occurring Peeling-bark Ochna (Ochna pulchra) and Ochna pretoriensis, both uniquely contributing to the PNBG and the surroundings biodiversity.

Chengdu Botanical Garden (Chengdu Park City Botanical Science Research Institute) was founded in 1983, located in Jinniu District, Chengdu City, Sichuan Province, China. There are more than 3,000 species of plants in the botanical garden, including nearly 1,800 species of woody plants, and 14 specialized gardens. After decades of development and research, Chengdu Botanical Garden has independently cultivated nearly 40 hibiscus varieties, collected 213 domestic and 23 foreign geographical species hibiscus resources, and 6 closely related species. At present, the reserve of hibiscus resources is the world's largest. Since 1988, Chengdu Botanical Garden has devoted itself to the collection, preservation, propagation and cultivation of viburnum plant germplasm resources, and built a viburnum garden, becoming the first special garden for preserving viburnum plant resources in China.

The University of Washington Botanic Gardens dates back to 1934 with the opening of what is now the Washington Park Arboretum.  The Arboretum was originally laid out from a plan designed by the Olmsted Brothers landscape architecture firm, and is highlighted by the ¾ mile long Azalea Way and numerous taxonomic, ecogeographic and horticultural displays.  The Arboretum features one of the most diverse woody plant collections in temperate North America, and is located on 230 acres near downtown Seattle.  Since 1980, the UW Center for Urban Horticulture has offered an additional site and room for expanding facilities.  Combined, the UW Botanic Gardens contains 320 acres with over 4,500 taxa and 40,000 plants.  Other than the Japanese Garden, which is managed by the city of Seattle within the Arboretum, both sites are free to visit and open every day of the year from dawn to dusk.