Got Nature? Blog

Figure 1. Norway maple is an invasive species that can resemble black and sugar maple. Photo by Purdue Arboretum.

Purdue Landscape Report: These three maples have somewhat similar-looking leaves. On the surface, you may think this is simply an academic exercise. But if you care about invasive plants and local ecology, this distinction is an important one.

Norway maple is an invasive tree species, while sugar and black maples are native tree species (sometimes called hard maples). Sugar and black maples are even more beloved for their gift of delicious sugary sap that can be made into maple syrup and similar products. They also make great shade trees. Note that there are other native and non-native maple species.

One way to distinguish between Norway (Acer platanoides), sugar (Acer saccharum), and black (Acer nigrum) maples is to count the number of lobes on the leaves. Lobes are large areas of the leaf that stick out, like an ear lobe, although that is not the clearest analogy. Norway maples typically have 5-7 lobes (commonly 7), sugar maples typically have 5, and black maples typically have 3-5. Black maple’s bottom two lobes are so much less prominent than sugar maple that it often looks like 3 main lobes. Additionally, black maple leaves droop on the sides, almost like they are starting to wilt from lack of water.

Another way to distinguish Norway maples from native maples (sugar and black) is to look at the winged seeds, called samaras. Children may call these “helicopters,” as they twirl on their way to the ground. The Norway maple has paired samaras arranged like a handlebar mustache. Sugar and black maple samara pairs look more like a Fu Manchu mustache, pointing downward rather than the near horizontal arrangement of Norway maple samaras.

Figure 2c. Black maple leaf. Photo by Purdue Arboretum.

Figure 2b. Sugar maple leaf. Photo by Purdue Arboretum.

Figure 2a. Norway maple leaf. Photo by Purdue Arboretum.

A third way to distinguish Norway maples from native maples is to snap off the long leaf stem (petiole). Norway maples have a milky latex sap that exudes if you squeeze or pinch a petiole, while native maples have clear sap.

There are a few other identification nuances between these species. For example, black maples have stipules (leaf-like growths) at the base of their petioles (absent on sugar maple). They also have pubescence or hairiness on the underside of the leaves. Norway maple has hairs in the axils of leaf veins. Norway maple’s leaves are generally broader than long. Other differences may be seen in the bark, twigs, buds, and fall coloring.

Although Norway maple is an invasive species, it has been a long-time landscaping favorite of homeowners, especially cultivars like ‘Crimson King’ that retain their deep red color all year. This attribute has made Norway maple a popular choice because few other options exist to offer that color feature for the landscape. Other varieties or cultivars exhibit the normal green leaf color. Native to northern Europe, the tree was introduced in America in the late 1700s. George Washington reportedly purchased two trees in 1792 to plant at Mount Vernon.

For full article: Distinguishing Between Norway, Sugar, and Black Maples, Purdue Landscape Report.

Resources:
ReportINvasive, Purdue College of Agriculture
What are Invasive Species and Why Should I Care?, Got Nature? Blog, Purdue Extension – Forestry and Natural Resources
Large Spots on Maple Leaves that Look Like Tar, Purdue Extension News
Find an Arborist, International Society of Arboriculture
Fifty Common Trees of Indiana
An Introduction to Trees of Indiana
Native Trees of the Midwest, The Education Store
Shrubs and Woody Vines of Indiana and the Midwest, The Education Store
Tree Installation: Process and Practices, The Education Store
Planting Your Tree Part 1: Choosing Your Tree, Video, Purdue Extension – Forestry & Natural Resource (FNR) YouTube Channel
Investing in Indiana Woodlands, The Education Store
Forest Improvement Handbook, The Education Store
ID That Tree, Purdue Extension-FNR YouTube playlist
Purdue Plant and Pest Diagnostic Laboratory

John E. Woodmansee, Extension Educator – Agriculture and Natural Resources (ANR)
Purdue Extension – Whitely County