Acer glabrum is a species of maple native to western North America, from southeastern Alaska, British Columbia and western Alberta, east to western Nebraska, and south through Washington, Montana and Colorado to California, Arizona and New Mexico.
It is a deciduous shrub or small tree growing to 10 m tall, with a trunk up to 20-30 cm diameter. The leaves are 2-10 cm broad, three-lobed (rarely five-lobed), variable in the depth of lobing, occasionally so deeply lobed as to be divided into three leaflets; the lobes have an acute apex and a coarsely serrated margin. The flowers are produced in corymbs of five to ten, yellowish-green, at the same time as the new leaves in spring. The fruit is a samara with two winged seeds.
There are four to six varieties, some of them treated by some authors at the higher rank of subspecies:
- Acer glabrum var. glabrum (syn. subsp. glabrum; Rocky Mountain Maple)– Rocky Mountains, Montana to New Mexico
- Acer glabrum var. diffusum (Greene) Smiley (syn. subsp. diffusum (Greene) A.E.Murray; Rocky Mountain Maple) – eastern California, Nevada, Utah
- Acer glabrum var. douglasii (Hook.) Dippel (syn. subsp. douglasii (Hook.) Wesm.; Douglas Maple) – Alaska south to Washington and Idaho
- Acer glabrum var. greenei Keller (Greene's Maple) – central California
- Acer glabrum var. neomexicanum (Greene) Kearney & Peebles (syn. subsp. neomexicanum (Greene) A.E.Murray; New Mexico Maple) – New Mexico
- Acer glabrum var. torreyi (Greene) Smiley (syn. subsp. torreyi (Greene) A.E.Murray; Torrey Maple) – northern California
It is sometimes referred to as "rock maple", due to the extreme hardness of the wood, which often requires special cutting tools.
It is plentiful in many parts of the Rocky Mountains
, often growing with Ponderosa Pine
, and Trembling Aspen