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  3. Norway maple

Norway maple

Acer platanoides

Summary 4

Acer platanoides, commonly known as the Norway maple, is a species of maple native to eastern and central Europe and western Asia, from Spain east to Russia, north to southern Scandinavia and southeast to northern Iran. It was introduced to North America in the mid-1700s as a shade tree. It is a member of the family Sapindaceae.

Short Description 5

This deciduous tree typically grows 13 to 19 m (40-60 ft) tall but can grow up to 28 m (90 ft) or more. Usually, it has a large canopy with yellow flowers in the spring and two winged samaras as fruits. The leaves are opposite, five-lobed, and coarsely toothed, and have a milky liquid when torn. In the fall, the leaves turn yellow. Abundant anywhere near a mature Norway maple tree.

Source: EwA Invasive Pocket Fieldguide | © Earthwise Aware

Classification and Identification 6

The Norway maple is a member (and is the type species) of the section Platanoidea Pax, characterised by flattened, disc-shaped seeds and the shoots and leaves containing milky sap. Other related species in this section include Acer campestre (field maple), Acer cappadocicum (Cappadocian maple), Acer lobelii (Lobel's maple), and Acer truncatum (Shandong maple). From the field maple, the Norway maple is distinguished by its larger leaves with pointed, not blunt, lobes, and from the other species by the presence of one or more teeth on all of the lobes.

It is also frequently confused with the more distantly related Acer saccharum (sugar maple). The sugar maple is easy to differentiate by clear sap in the petiole (leaf stem); Norway maple petioles have white sap. The tips of the points on Norway maple leaves reduce to a fine "hair", while the tips of the points on sugar maple leaves are, on close inspection, rounded. On mature trees, sugar maple bark is more shaggy, while Norway maple bark has small, often criss-crossing grooves. While the shape and angle of leaf lobes vary somewhat within all maple species, the leaf lobes of Norway maple tend to have a more triangular (acuminate) shape, in contrast to the more finely toothed lobes of sugar maples, that narrow towards the base. Flowering and seed production begins at ten years of age, however, large quantities of seeds are not produced until the tree is 20. As with most maples, Norway maple is normally dioecious (separate male and female trees), occasionally monoecious, and trees may change gender from year to year.

The fruits of Norway maple are paired samaras with widely diverging wings, distinguishing them from those of sycamore, Acer pseudoplatanus which are at 90 degrees to each other. Norway maple seeds are flattened, while those of sugar maple are globose. The sugar maple usually has a brighter orange autumn color, where the Norway maple is usually yellow, although some of the red-leaved cultivars appear more orange.

The flowers emerge in spring before the leaves and last 2-3 weeks. Leafout of Norway maple occurs roughly when air temperatures reach 55°F (12°C), and there are at least 13 hours of daylight. Leaf drop in autumn is initiated when day lengths fall to approximately 10 hours. Depending on the latitude, leaf drop may vary by as much as three weeks, beginning in the second week of October in Scandinavia and the first week of November in southern Europe. Unlike some other maples that wait for the soil to warm up, A. platanoides seeds require only three months of exposure to temperatures lower than 4 °C (40 °F) and will sprout in early spring, around the same time that leafout begins. Norway maple does not require freezing temperatures for proper growth, however it is adapted to higher latitudes with long summer days and does not perform well when planted south of the 37th parallel, the approximate southern limit of its range in Europe. Further, most North American Norway maples are believed to have descended from stock brought from Germany, at approximately 48N to 54N, not the more southerly ecotypes found in Italy and the Balkans that evolved for similar lighting conditions as the continental United States. The heavy seed crop and high germination rate contribute to its invasiveness in North America, where it forms dense monotypic stands that choke out native vegetation. The tree is also capable of growing in low lighting conditions within a forest canopy, leafs out earlier than most North American maple species, and its growing season tends to run longer as the lighting conditions of the United States (see above) result in fall dormancy occurring later than it does in the higher latitude of Europe. It is one of the few introduced species that can successfully invade and colonize a virgin forest. By comparison, in its native range, Norway maple is rarely a dominant species and instead occurs mostly as a scattered understory tree.

As an invasive species in North America 4

The Norway maple was introduced to northeastern North America between 1750 and 1760 as an ornamental shade tree. It was brought to the Pacific Northwest in the 1870s. Today, Norway maples tend to be most common in the Pacific Northwest, in southern Ontario, and along the Kennebec river in southern Maine. The roots of Norway maples grow very close to the ground surface, starving other plants of moisture. For example, lawn grass (and even weeds) will usually not grow well beneath a Norway maple, but English Ivy, with its minimal rooting needs, may thrive. In addition, the dense canopy of Norway maples can inhibit understory growth. Some have suggested Norway maples may also release chemicals to discourage undergrowth, although this claim is controversial. A. platanoides has been shown to inhibit the growth of native saplings as a canopy tree or as a sapling. The Norway maple also suffers less herbivory than the sugar maple, allowing it to gain a competitive advantage against the latter species. As a result of these characteristics, it is considered invasive in some states, and has been banned for sale in New Hampshire and Massachusetts. The state of New York has classified it as an invasive plant species. Despite these steps, the species is still available and widely used for urban plantings in many areas.

Fruit (samara): note the flat seed capsule and the angle of the "wings"

Typical yellow fall foliage

Atypical orange-red fall colour

Purple leaves of cultivar 'Schwedleri'

Twig and buds

🚧 Control Methods (EwA Content Development in Progress) 5

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Sources and Credits

  1. (c) Kate Danziger, some rights reserved (CC BY-ND), uploaded by Kate Danziger, https://www.inaturalist.org/observations/80037208
  2. (c) gsarajg, some rights reserved (CC BY-ND), uploaded by gsarajg, https://www.inaturalist.org/observations/75577552
  3. (c) Claire O'Neill, some rights reserved (CC BY-ND), https://www.inaturalist.org/observations/43456352
  4. (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Acer_platanoides
  5. (c) Claire O'Neill, some rights reserved (CC BY-SA)
  6. Adapted by Claire O'Neill from a work by (c) Wikipedia, some rights reserved (CC BY-SA), https://en.wikipedia.org/wiki/Acer_platanoides

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