Rocky Mountain maple (Acer glabrum) is a erect shrub or, less often, a small tree. Although it can be larger, usually the smooth trunk with a red hue and greyish tint is only about 2 to 3 inches in diameter. The twigs are red, although a couple varieties have whitish twigs.
The deciduous, opposite Rocky Mountain maple leaves are simple, rarely compound. They have three major and two supplementary lobes, serrated margins and prominent veins. The leaf blades are green on the upper side and lighter green to greyish on the lower side. In autumn, Rocky Mountain maple leaves turn gold.
The inflorescence is a round cluster of 2 to 10 minute flowers with greenish-yellow petals. Each plant can be complete with both male and female flowers or have only male or only female flowers.
Maple fruits are double, straw colored or reddish samaras (a pair of winged seeds joined but easily separated when mature) without hairs.
Growing on rocky, montane slopes with poor, gravelly soil, Rocky Mountain maple is found throughout much of the Western United States and Western Canada.
Rocky Mountain maples have a complex of forms (varieties and subspecies) that are treated differently by different botanists. Mountain maple, dwarf maple and Sierra maple are only three other common names, among many more, for A glabrum.
This Rocky Mountain maple was photographed in June at the Baby Foot Lake Trailhead in the Kalmiopsis Wilderness (Oregon).