Acer platanoides (Norway Maple)

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

Description

Acer platanoides is a deciduous tree, growing to 20–30 m (65–100 ft) tall with a trunk up to 1.5 m (5 ft) in diameter, and a broad, rounded crown. The bark is grey-brown and shallowly grooved. Unlike many other maples, mature trees do not tend to develop a shaggy bark. The shoots are green at first, soon becoming pale brown. The winter buds are shiny red-brown.

The leaves are opposite, palmately lobed with five lobes, 7–14 cm (2 3⁄4–5 1⁄2 in) long and 8–20 cm or 3 1⁄4–7 3⁄4 in (rarely 25 cm or 9 3⁄4 in) across; the lobes each bear one to three side teeth, and an otherwise smooth margin. The leaf petiole is 8–20 cm (3 1⁄4–7 3⁄4 in) long, and secretes a milky juice when broken. The autumn colour is usually yellow, occasionally orange-red.

The flowers are in corymbs of 15–30 together, yellow to yellow-green with five sepals and five petals 3–4 mm (0–1⁄4 in) long; flowering occurs in early spring before the new leaves emerge. The fruit is a double samara with two winged seeds. the seeds are disc-shaped, strongly flattened, 10–15 mm (3⁄8–5⁄8 in) across and 3 mm (1⁄8 in) thick. The wings are 3–5 cm (1 1⁄4–2 in) long, widely spread, approaching a 180° angle. It typically produces a large quantity of viable seeds.

Under ideal conditions in its native range, Norway maple may live up to 250 years, but often has a much shorter life expectancy; in North America, for example, sometimes only 60 years. Especially when used on streets, it can have insufficient space for its root network and is prone to the roots wrapping around themselves, girdling and killing the tree. In addition, their roots tend to be quite shallow and thereby they easily out-compete nearby plants for nutrient uptake.Norway maples often cause significant damage and cleanup costs for municipalities and homeowners when branches break off in storms as it does not have strong wood.

Classification and identification

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 shape, in contrast to the more squarish lobes often seen on sugar maples.

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 tree tends to grow out leaves earlier than most maples and holds its leaves somewhat longer in autumn. Seeds begin to be forming in mid-spring and ripen over the course of the summer months, finally dropping in the fall. 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. The heavy seed crop and high germination rate contributes to its invasiveness in North America, where it forms dense monotypic stands that choke out native vegetation. 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.

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