Rocky Mountain Maple
Acer glabrum
Original Species Paper by Lois Wythe
Aceraceae
The only maple native to North Idaho grows as a shrub or small tree. It is a sprawling kind of shrub and needs a yearly pruning to keep it neat, if it develops as a multi-trunk shrub, growing to four to six feet tall and as wide across. As a tree, it can grow to as high as 33 feet. The Idaho champion in the Sawtooth National Forest was 25 feet tall in 1973 and was 16.9 inches in circumference. It has a 3.7 ft. crown. The National champion is also in Idaho, in the closer Clearwater National Forest and had reached 47 feet tall in that same year and had a 38 in. circum.
Stems: Until the tree is quite old, the stems are a smooth, reddish-purple. Old trees have grayish bark.
Buds: Opposite, smooth, reddish, and plump, about 3 mm. long. Bud scales are paired.
Leaves: Opposite, deciduous, 3 to 5 toothed, with the typical maple shape. The dark green leaves sometimes have a reddish tint. Their greatest glory is the fall display of red and yellow leaves, often with the red predominating.
Flowers: Small, a yellow-green color in short terminal or auxiliary clusters. Flowers appear with the leaves in April to June.
Fruit: Double winged fruits sometimes called "keys". When they fall, they do so in spirals, slowly, and are fun to watch. When dry, they are sold as potpourri ingredients in woodsy mixes.
Medicinal Uses: To the best of my knowledge, these maples have no medicinal use although a few old sources mention that the Indians made an eye tonic from the roots -- presumably of this native.
Landscape use: These are LARGE shrubby trees and they need space to spread out.
They are so spectacular in the fall that they should be placed where they can be viewed from picture windows; and even when their leaves fall, they remain highly colored for a couple of weeks and are like a brilliant carpet around the tree.
If you order: Be sure that the plant you buy is Acer glabrum and not the more common Acer rubrum, the red maple tree.
Habitat: Well drained and (in my experience) moist soil. I have two specimens-about the same age and size--and the one growing in a grove of tamarack and huckleberry has always had only yellow leaves. In that location, it does not receive much water, and is shaded most of the time. On the other hand. the shrubby tree on a south, well-drained slope, near a pond where it probably does receive some sub- irrigation, does a spectacular number in autumn, and so I have concluded that a mostly sunny location is probably best.
At the Arboretum we have several Rocky Mt. Maples, but they are still quite small and so far have not produced red leaves.