By Anthony S. Aiello, The Gayle E. Maloney Director of Horticulture and Curator

Acer ceriferum.

Acer pycnanthum.

As we all know, autumn is one of the finest seasons in the Northeast, with the annual arrival of fall color being one of the highlights of the year.  At the Arboretum, the display reaches its climax in October, with maples being one of the most significant contributors to our display.  Our maple collection is comprised of species from North America, Europe, and Asia. In October, our native sugar maple (Acer saccharum) and red maple (Acer rubrum) are among the most brilliant contributors to the autumn display, followed by Japanese maples (Acer palmatum) in early November.  

But there is much more to our maple collection than good fall color; contributing to the display is an internationally recognized collection, developed over the course of several decades through propagation along with domestic and international plant exploration.  Overall, we have close to 500 maples of over 150 types, from ones seen frequently in cultivation to ones that are among only a handful of plants in North America.

The recently released Red List of Acer describes the conservation status of all 158 maple species from around the world.  Carried out by Botanic Gardens Conservation International, this assessment is part of an effort to determine threats to maple and other tree species, and to determine plans for conserving these species. Maples are native throughout the Northern Hemisphere, and many of them (61%) have an economic use, including horticulture, medicine, food, and construction materials.  The Red List was developed to determine which species are threatened and how many of these species are held in ex situ, that is, in botanic garden collections.  According to the List, 23% of all maple species are threatened, meaning that 36 species have significant levels of threat in their natural habitats. Among the most threatened, 14 species are not held in any botanic garden collection. And while the primary goal should always be habitat preservation there are cases where natural populations are so restricted and vulnerable that preserving these in cultivation is the only method available. A famous example of this is the Franklin tree (Franklinia alatamaha), extinct in the wild in coastal Georgia and preserved only in cultivation.

The Arboretum has several of the threatened (or listed) maples, from the horticulturally well-known paperbark maple (Acer griseum) threatened in its native habitat in central China, Acer pycnanthum, a Japanese close relative of our red maple, and Acer yui, found only in a restricted area in Gansu and Sichuan provinces. All of these are part of our long-term research program and allow us to study how these species perform in cultivation, provide insights into ways to propagate them, and become a touchstone for continued efforts in conservation. More information on the Red List of Acer can be found at, with the complete report can be found at

Acer griseum.