Norway Maple (Acer platanoides)

A grouping of green Norway maple leaves and yellow Norway maple flowers.

 
 

Norway maple has been widely planted in the U.S. as an urban street tree. It spreads by seeds into nearby disturbed forest communities, where its dense canopy reduces light levels and limits growth of wildflowers and tree seedlings.

Description

Appearance

Norway maple is a large deciduous tree with a dense canopy. Trees can reach 40-60 feet tall, with a dense, rounded and symmetrical crown. Leaves typically turn yellow in the fall season, although there is a popular landscaping cultivar known as "Crimson King" that has a deep reddish purple fall foliage.

Leaves and stem

Leaves are dark green, four to seven inches wide and have five lobes. Leaves typically turn pale yellow in the fall, but there is a popular cultivar that has deep reddish purple fall foliage. Leaves are located in pairs opposite each other along twigs. Norway maple can be distinguished from other maple species by the milky white fluid that oozes when the stem of a leaf is broken. The bark is grayish-brown, with regular grooves or furrows.

Flowers

Tiny, yellow-green flowers grow in loose, upright clusters. They bloom in May, and begin to bloom before the leaves emerge.

Seeds

Numerous 1-2 inch long fruit mature in autumn. Fruits are double-winged samaras (helicopter seeds), typical of maple trees. The two winged seeds are very widely spread, nearly straight across from each other, rather than a V-shape. Seeds are spread by wind. Norway maples typically produce heavier than normal seed crops every three to five years.

Roots

Norway maple has shallow roots that can compete with other plants in the landscape and can cause damage to pavement in urban areas.

Biology

Norway maple can tolerate a wide range of soil conditions, including acidic soils and soil textures ranging from sand to clay. It can also tolerate hot and dry conditions, ozone, and sulfur dioxide air pollution. This hardiness to harsh conditions makes it well-suited for urban plantings in landscaping and along city streets. Its winged seeds are dispersed by wind, but usually not very far, so dense colonies of young plants are common. Norway maple leafs out early in spring and holds its leaves longer into the fall than native trees and shrubs.

Origin and spread

It is native to Europe and widely sold in nurseries in the U.S. Although sold primarily as an urban street tree, it spreads by seeds into nearby disturbed forest communities. It has been widely planted in the U.S., from the Canadian border south to the Carolinas. For the current distribution of Norway maple in Minnesota, visit EDDMapS distribution maps.

Don't be fooled by these look-alikes

Sugar maple, Acer saccharum (native) – Norway maple emits milky sap when leaf stem is broken; fruit of Norway maple has a much wider angle (straighter) than sugar maple fruits; typical fall color of Norway maple is yellow, although there is a popular cultivar that turns deep reddish purple in the fall.

 
Regulatory classification

This species is a Minnesota Department of Agriculture Specially Regulated Plant. Sellers must affix a label that advises buyers to only plant Norway maple and its cultivars in landscapes where the seedlings will be controlled by mowing and other means. Norway maple should be planted at least 100 yards from natural areas.

Threat to Minnesota
  • The dense canopy of Norway maple limits the growth of sugar maple and other native tree seedlings, reducing forest diversity.
  • Wildflower diversity is reduced beneath Norway maple because the dense canopy reduces light levels.
  • Shallow roots can compete for water with other plants in the landscape, including grasses, and can damage pavement in urban areas.
What you should do

One way that invasive plant seeds and fragments can spread is in soil.  Sometimes plants are planted purposefully.  You can prevent the spread of invasive plants.

PlayCleanGo: Stop Invasive Species in Your Tracks

  • REMOVE plants, animals and mud from boots, gear, pets and vehicles.
  • CLEAN your gear before entering and leaving the recreation site.
  • STAY on designated roads and trails.
  • PLANT non-invasive species.
Native substitutes
 
Control methods

Mechanical control can be done by pulling seedlings by hand when the soil is moist.

Herbicide control can be done by cutting the stem and applying glyphosate or triclopyr to the cut stump. Oil-based triclopyr ester products can also be sprayed along the base of an un-cut stem, coating all sides of the lower 12-18 inches of the main stem. These are systemic herbicides that are taken up by plants and move within the plant, which can kill leaves, stems, and roots.

Reporting

If you would like to add to the public information about this species, you can report occurrences outside of plantings by submitting a report through EDDMapS. If you see plants being sold without the label required by the Minnesota Department of Agriculture, you can report that by emailing Report a Pest, calling Report a Pest (1-888-545-6684), or contacting your local county agricultural inspector

Resources

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