Norway Maple is a medium size deciduous tree that grows to 40 to 70 feet high and up to 2 feet in diameter, and has a dense rounded crown. The tree is considered invasive in Minnesota and in other states. However, it forms an excellent shape for a landscape tree but the easily germinated seeds will take over an area unless control measures are in place.
The bark is gray or brown, somewhat corky and, with age, developing shallow furrowed long narrow ridges that sometimes interlace.
Twigs are stout, hairless, brown, with light colored lenticels, with large terminal buds that are green-purple with large scales. The visual effect is of a turban.
Leaves are opposite, simple, 5 to 7 palmate lobes with long pointed teeth on the lobes and wavy edges, and a little wider than long (up to 6 inches long and 7 inches wide). They are dark green above and paler below. The main veins radiate from the base and appear sunken on the surface of the leaf. The base is truncate or a bit heart-shaped. Leaf stalks are long and slender, exuding white milky sap when broken. Fall color is yellow.
Flowers: The tree can be monoecious, that is with separate male and female flowers or it is dioecious, with the flowers on different trees, which is the usual case. Male flowers (staminate) are produced in a 2 to 3 inch wide flat-topped cluster (a corymb) containing 10 to 30 flowers, each of which is quite small (no more than 1/3 inch across), greenish-yellow, with 5 petals, 5 sepals and eight stamens rising from a greenish central nectary disc. Each flower has a long smooth stalk. Female flowers (pistillate) appear in a similar arrangement and color but have sterile stamens (staminodes) and a pistil with a pair of small wing-like structures. Flowers appear on the twigs of the prior years growth with the leaves. Fall color is yellow.
Seed: Female flowers mature to a one-seeded samara, about 1-1/2 to 2 inches long, with a broad wing that is paired with another seed forming an angle that is just under 180 degrees, green initially and turning yellow to light brown. These mature in late summer to fall and germinate the following Spring; some persist into winter and when they drop from the tree, are wind dispersed.
Habitat: Norway Maple grows best in moist, adequately drained fertile soils. It grows less well on sandy soils, soils high in clay or high in lime. Seedlings are very shade tolerant and the entire tree is tolerant of dust and city smoke and haze.
Names: The genus, Acer, is the Latin word for 'maple'. The species name, platanoides, is derived from two words meaning 'like the Plane Tree' referring to a similarity to the leaf of the Plane Tree which is another European tree, not related to our species. The author name for the plant classification - 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. Botanists have recently move the maples into the Sapindaceae family from the older Aceraceae family.
Comparisons: The closest confusing tree would be the Sugar Maple, Acer saccharum, but there the buds are medium brown, the sap is clear, and the leaves longer than wide. Norway Maple has the samaras paired at a much larger angle.
Above: 1st photo - Note the dense rounded crown. 2nd photo - Old trees have bark furrowed into scaly ridges. 3rd photo - Twigs are brownish with light color lenticels. Buds are greenish-purple with large scales. Terminal buds look like turbans.
Below: Flowers occur in erect rounded clusters, usually with the leaves or just before. Male and Female are separate. 2nd photo is a female flower. Note the wings on the pistil. The stamens are sterile (staminodes).
Below: 1st photo - Male flowers have the fertile stamens rising from a greenish central disc. 2nd photo - Seeds are in paired samaras which have an angle of separation approaching 180 degrees - the most of the maples in our area.
Below: 1st photo - The leaves are wider than long and each of the 5 lobes has points. Veins appear sunken. 2nd photo - An interesting landscape variety of the Norway Maple is var. schwedleri, which has pink to reddish flowers and deep maroon leaves.
Below: A leaf comparison of the common maples. Images not to scale.
Notes: Norway Maple's date of appearance in the Garden was April 30, 1948 when Martha Crone planted it along with six other tree species; strangely, she did not list it on her 1951 census, nor was it listed in 1986. However the example in the Garden is quite large and it must have been mis-classified in the past. Norway Maple is native to Europe and Western Asia and was brought to the U.S. in the late 1700s. Over 100 cultivars have been developed in North America for the nursery trade. A commonly seen cultivar is 'Crimson King'. The tree has spread in the wild to the entire NE section of North America, south as far is Tennessee and North Carolina with Minnesota on the western edge of the range. Because of its use in the nursery trade, it is also found on the west coast in British Columbia, WA, OR, ID and MT.
Invasive: It is widely planted as a landscape tree and has escaped to the wild where it is now an invasive threat. In Minnesota it is listed by the DNR as a non-native invasive plant as it is more aggressive than the native Sugar Maple. It is vary shade tolerant and produces large numbers of shade tolerant seedlings. It's dense canopy of leaves prevent native forbs from growing beneath it.
Eight species of Maple are found in the wild in Minnesota: A. negundo, Box Elder; A. nigrum, Black Maple; A rubrum, Red Maple; A. saccharinum, Silver Maple; A. saccharum, Sugar Maple; A. spicatum, Mountain Maple; A. ginnala, Amur Maple and A. platanoides, Norway Maple. The latter two are not native but introductions that have naturalized.
Uses: Norway Maple and its cultivars are primarily landscape trees. There is little reported use for wood and wood products. However in earlier times the wood was employed for a number of uses as it is white, fine grained and easily worked. Maple Syrup can be made by tapping the trees and processing in the ususal methods. Jenny Tollefson on Missoula MT, where the Norway Maple is plentiful and the Sugar Maple is non-existant, says it is golden-amber in color and intensely sweet.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"