Acer platanoides (Norway maple) is a species of maple native to eastern and central Europe and southwest Asia, from France east to Russia, north to southern Scandinavia and southeast to northern Iran.
It is a deciduous tree, growing to 20–30 m tall with a trunk up to 1.5 m 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 long and 8–20 cm (rarely 25 cm) across; the lobes each bear one to three side teeth, and an otherwise smooth margin. The leaf petiole is 8–20 cm 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 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 across and 3 mm thick. The wings are 3–5 cm long, widely spread, approaching a 180° angle. It typically produces a large quantity of viable seeds. It is not particularly a long-lived tree, with a maximum age of around 250 years.
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 identify by clear sap in the petiole (Norway maple has 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 seeds of sugar maple are globose, while Norway maple seeds are flattened. 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 leaf out earlier than most maples and holds its leaves somewhat longer in autumn.
Cultivation and uses
Norway maple has been widely placed into cultivation in other areas, including western Europe northwest of its native range. It grows north of the Arctic Circle at Tromsø, Norway. In North America, it is grown as a street and shade tree as far north as Anchorage, Alaska. It is favoured due to its tall trunk and tolerance of poor, compacted soils and urban pollution.
It has become a popular species for bonsai in Europe and is used for medium to large bonsai sizes and a multitude of styles.
Many cultivars have been selected for distinctive leaf shapes or colourations, such as the dark purple of 'Crimson King' and 'Schwedleri', the variegated leaves of 'Drummondii' and 'Emerald Queen', and the deeply divided, feathery leaves of 'Dissectum' and 'Lorbergii'. The purple-foliage cultivars have orange to red autumn colour. 'Columnare' is selected for its narrow upright growth.
- Weeping Norway Maple, Acer platanoides 'Pendulum'
As an invasive species in North America
Norway maples release chemicals to discourage undergrowth, which tends to create bare, muddy run-off conditions immediately under the tree. 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 in New Hampshire and Massachusetts. The Norway maple is one of three species Meijer Garden Centers no longer sell; Meijer made this decision due to the tree's invasive nature. Despite these steps, the species is still available and widely used for urban plantings in many areas.
The Norway maple is threatened in a few areas by the Asian long-horned beetle, which eats through the trunks, often killing the trees.
A number of species of Lepidoptera feed on Norway maple foliage. Norway maple is generally free of serious diseases, though can be attacked by the powdery mildew Uncinula bicornis, and verticillium wilt disease caused by Verticillium spp. "Tar spots" caused by Rhytisma acerinum infection are common but largely harmless.
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