Flower:

Round, branching, upright clusters about 2 inches across appear just prior to or at the same time leaves emerge in spring. Male and female flowers may be on separate trees or the same tree. For both, the flowers open broadly, are ¼ to 1/3 inch across, greenish yellow with 5 oval-lance sepals up to 1/8 inch long and 5 spatula shaped petals nearly twice as long as the sepals. In the center is a brownish green disk. Male flowers have 8 spreading stamens around the disk, females a 2-part, curled style in the center. Flower stalks are long, slender and hairless or glandular-hairy.

Leaves and bark:

Leaves are simple, opposite, and long stalked, the blade up to 8 inches long and 10 inches wide with 5 to 7 palmate, sharply pointed lobes, the two basal lobes a single sharp point. Leaf edges are smooth and often wavy. Upper surface is dark green (though this can vary with the cultivar) and smooth, the lower surface paler and smooth except for dense patches of stiff hairs in the vein axils and short stiff hairs on the veins near the axils.

One year old twigs are reddish brown and smooth, older branches turning grayish to brown like the trunk. The bark is moderately textured by furrows and ridges. The national champion in the US is over 6 feet in diameter at breast height (dbh).

Fruit:

Fruit is a pair of winged seeds (samara), that can be up to 2½ inches long (though this can also vary with the cultivar) and are widely angled apart to nearly 180°. Fruit matures from September into October.

Notes:

As its name implies, this is a maple native to Norway and much of Europe into western Asia. It was introduced in colonial times as an urban street tree and is still widely bought and sold for that purpose today. Many years of horticultural selection has produced cultivars that vary widely in form, from columnar to densely global and leaf color with red maroons, bright yellow and even variegated. But it has escaped human cultivation into natural systems where it has become a component of successional forests. It is highly shade tolerant and mature trees produce such dense canopies, little light is provided for understory and ground layer plants beneath them and makes for serious competition with our highly prized native Sugar Maple. While the misinformed often automatically identify its red leaved cultivars as "red" maples, it shares few similarities with our native Red Maple (Acer rubrum). Except for its distinctive flowers in the spring and widely angled seeds in the fall, green varieties are most often confused with the native Sugar Maple (Acer saccharum). Norway Maple leaves are generally bigger and more sharply pointed, the points longer and more tapering than Sugar Maple, and both upper and lower surfaces darker green. Few Norway Maples provide meaningful fall color, a few yellows at most and often persisting on the tree until late season frosts before turning a drab olive brown. Still when in doubt, the easiest way to ID Norway Maple is to tear a leaf or snap a leaf stalk in two and look for the milky sap the fresh break produces.