Editing Acer platanoides (section)

== Classification and identification ==
[[File:Ahorn bluehend2.JPG| thumb|Tree in flower]]
[[File:Norway-maple-bark.jpg|thumb|Bark]]

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.<ref name=rushforth /><ref name=afm />

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 (botany)|petiole]] (leaf stem); Norway maple petioles have white sap.{{citation needed|date=November 2022}} 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.{{citation needed|date=November 2022}} 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.<ref name=Stace/>{{rp|397}} Flowering and seed production begins at ten years of age; however, large quantities of seeds are not produced until the tree is 20. The Norway maple is [[Sequential hermaphroditism|heterodichogamous]]—meaning there are both protogynous and protandrous trees (and, more rarely, duodichogamous trees)—and individual trees may change sexual expression from year to year.<ref>{{cite journal
|last1       = Liesebach
|first1      = Heike
|last2       = Schneck
|first2      = Dagmar
|date        = 2022
|title       = Flowering behavior of clones in a Norway maple (Acer platanoides) seed orchard and mating system analysis using nuclear SSR markers
|url         = https://link.springer.com/article/10.1007/s10342-022-01459-3
|journal     =  European Journal of Forest Research
|volume      = 141
|pages       = 561–569
|doi         = 10.1007/s10342-022-01459-3
|access-date = March 31, 2025
|doi-access= free
}}</ref><ref>{{cite thesis
|last        = de Jong
|first       = P. C. 
|date        = 1976
|title       = Flowering and Sex Expression in Acer L.: a Biosystematic Study
|url         = https://www.proquest.com/openview/8eb51faf401cecf59eda6d296a9ebb9e/1
|degree      = Doctor in de Landbouwwetenschappen
|location    = Wageningen University
|access-date = March 31, 2025
}}</ref>

The fruits of Norway maple are paired [[samara (fruit)|samaras]] with widely diverging wings,<ref name=Stace>{{cite book|last=Stace|first=C.A.|year=2019|title=New flora of the British Isles|edition=Fourth|publisher=C. & M. Logistics Press|location = Suffolk, U.K.| isbn=9781527226302}}</ref>{{rp|395}} distinguishing them from those of sycamore, ''Acer pseudoplatanus'', which are at 90 degrees to each other.<ref name=Stace /> Norway maple seeds are flattened, while those of sugar maple are globose.{{citation needed|date=March 2016}} 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.
[[File:Acer platanoides in autumn colors.JPG|thumb|Norway maple in autumn]]
The flowers emerge in spring before the leaves and last 2-3 weeks. [[Leaf flushing|Leafout]] of Norway maple occurs roughly when air temperatures reach 55°F (12°C) and there is 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 {{convert|40|F|C|order=flip}} 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 descended from stock brought from Germany, at approximately 48°N to 54°N, 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 contributes 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.<ref name=rushforth /><ref name=afm />