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.


With climate change taking its toll on woodlands in the Northeast, trees are more important than ever, and there is a greater need for more tree ‘doctors’ according to the New York Times.

Morris Arboretum of the University of Pennsylvania is committed to training professionals in the care of trees. The Arboretum is a center for arboriculture education and continues to train new arborists as well as those that have been in the industry for many years. It offers more than 20 professional classes each spring and fall which earn CEU credits.

In September, after a decade without a Chief Arborist, Morris Arboretum was able to appoint a fully endowed position of Chief Arborist made possible by the McCausland Foundation and Janet and John Haas. Peter Fixler, the new Paul W. Meyer Chief Arborist has 20 years of experience, having worked for Bartlett, The Care of Trees (now Davey Tree), Longwood Gardens, and most recently has his own business as a Sub-contract climber. Peter has been actively involved in the Penn-Del ISA chapter since he started climbing trees and has been their Arbor Day Chair for 13 years. The Chief Arborist position will strengthen the Arboretum’s tree care program while also helping to advance arboriculture education and outreach programs.

This October, Morris Arboretum is hosting its 7th annual Tree Canopy Conference virtually, Tree Canopy Series: Building Environmental Resilience. This virtual conference focuses on preserving trees in our communities and examines important topics including tree equity, making the benefits of trees available to everyone. Participants will learn how forests respond to climate change, which tree species will do best as the climate warms, and the importance of planting diverse species. Participants will see how warmer temperatures change the geographic ranges of insect pests and what that means for preserving trees. Each session carries 1 CEU for International Society of Arboriculture certified arborists and costs $25. 

To register visit or call 215-247-5777, ext. 125. Sponsored by the Morris Arboretum of the University of Pennsylvania and the Haverford College Arboretum.


By Katherine Wagner-Reiss

Clerodendrum trichotomum (1981-337B), fruiting by the Hillcrest Avenue fence on 10/12/19. Grown from seed collected during the 1979 Expedition to Korea and Taiwan. Photo by Katherine Wagner-Reiss.

Clerodendrum trichotomum. Flowers with a sweet scent, reminiscent of jasmine. Notable long stamens. Ovate leaves that smell like raw peanut butter when crushed. Photo by Alexander Dunkel. CC-BY-SA-2.5.

Clerodendrum trichotomun is a shrub of peak garden interest in the fall. The genus name Clerodendrum, assigned by Linnaeus in 1753, is a play on the double meaning of the Greek word kleros. First, kleros means “chance” or “fate” and refers to the risk in taking Clerodendrum-derived medicines, since reports vary widely as to their efficacy and safety! Second, kleros also means “clergy” alluding to the fact that Clerodendrum was used in the Sinhalese religion. The second half of the genus name, dendrum, derives from the Greek word for tree. Linnaeus carried the pun even further: he gave the name Clerodendrum infortunatum to the first named species and the name Clerodendrum fortunatum to a subsequent species. Yes, botanists enjoy a good inside joke!

Most Clerodendrum species are native to tropical or warm temperate areas; luckily C. trichotomum, native to N. China and Japan, is winter hardy to USDA zone 6A and survives the winters at the Morris Arboretum, which is in zone 7A. The specific epithet trichotomum means branching into three, referring to the inflorescences (flower clusters) and infructescences (fruit clusters), which are both long-peduncled three-branched cymes.

The common name Harlequin Glorybower implies a parti-colored feature and a glorious bower, and Clerodendrum trichotomum delivers on both counts with its showy flowers and magnificent fruits: bright blue drupes surrounded by red calyces. Another common name is peanut butter tree; the crushed leaves smell like raw peanut butter.

While this beauty does not supply fall foliage color, it begins to display sweet-smelling white flowers in late summer, followed by iridescent fruits in fall. The shrub is easy to find because it is close to the Springhouse, a feature on the Morris Arboretum map. The Springhouse, originally used to keep perishables cool, was restored in 2004 and is one of the few remaining examples of a springhouse in Philadelphia. See the mapped location of Clerodendrum trichotomum and the Springhouse at Collection Connection

According to Tony Aiello, curator and director of horticulture at the Arboretum, for the past year or so he has become concerned about Clerodendrum as a potential invasive because they are finding it popping up around the Arboretum, often at some distance from the parent plant. So, while the fruits are attractive to us, apparently the birds like them as well. Based on its unexpected occurrences, the Arboretum staff have been thinking of removing the large mass next to the Springhouse. As with other non-native plants at the Morris, the staff are always vigilant for plants that wander around, trying to keep the proverbial horse in the barn.
Katherine has her Certificate in Botany from the New York Botanical Garden and is a botanical tour guide and free-lance writer.

Infructescence, which shows obvious three-part branching explaining the specific epithet trichotomum: branching into three. Inedible metallic-blue fruits appeal to some birds. Photo by Katherine Wagner-Reiss.

View of the Springhouse complex when standing by the Clerodendrum trichotomum. The only existing Morris Arboretum structure that predates the Morrises living on the property. Photo by Katherine Wagner-Reiss.


Looking for a fun staycation this Labor day weekend? Morris Arboretum has activities for everyone! Reserve your advance ticket online at and take in all the sights and sounds:

Grab your masks and head to your first stop—Out on a Limb,  a 50 foot high treetop canopy.
From there it’s a short walk to the beautiful Rose Garden with a bubbling fountain in the center.
Continue down the path to the Garden Railway. Model trains zip along a quarter-mile track.
If it’s time for a snack, enjoy a picnic and a rest in the Azalea Meadow with John and Lydia Morris.
At the end of the Oak Allée, you can find fun self-directed activities to learn about all about seeds.
Continue along the path to the Spring House where it’s cooler—it once was a refrigerator.
Next up is the Swan Pond where swans Flora and Fauna glide gracefully through the water.
Don’t miss Loop de Loop, the huge maze made entirely of sticks... weave your way through it!
Last up is the Log Cabin where Lydia Morris entertained her guests with tea service.

So much to see and do for your visit…let us know if you discover something new! #morrisarboretum, @morrisarboretum