Norway Maple — Acer platanoides

Acer means hard or sharp; platanoides refers to the trees resemblance to a Sycamore tree. This tree is particularly well-suited to large cities since it seems to withstand dust, gases, and smoke.

This European native is somewhat borderline in hardiness for Colorado and may not perform well above 6,000’ elevation. It is subject to sudden, severe freezes, causing the tree to dieback at the branch tips or the bark to split open. Note the frost crack scars on the southwest side of this specimen. A count of the wound callus “rings” dates this scar to the severe winter of 1948-1949. In the more humid, rich soils of the eastern states, this species has naturalized and even become a “weed.” Here, however, it is slow-growing but valued for the very dense, much needed shade.

The tight bark and large, few-scaled reddish, opposite buds help to identify it in winter. In summer, the sharply- lobed leaves and winged fruit (samaras), often called “keys”, are easy to recognize.

An additional identifying feature in early summer is the milky sap which will ooze from the base of the leaf stalk (petiole) when removed from the twig. Fall color may be yellow but this depends upon how early a killing frost occurs. If early, the leaves may turn brown and fall off. Purple-leaf forms of Norway maple are sold locally under the names ‘Schwedler’, ‘Fassens Black’, and ‘Crimson King’.

http://en.wikipedia.org/wiki/Norway_Maple