Acer glabrum

Rocky Mountain maple


The Basics

Taxonomy: Kingdom - Plantae (plants). Subkingdom - Tracheobionta (vascular plants). Superdivision - Spermatophyta (seed plants). Division - Magnoliophyta (flowering plants). Class - Magnoliopsida (dicotyledons). Subclass - Rosidae. Order - Sapindales. Family - Sapindaceae (maple). Genus - Acer L. Species - Acer glabrum Torr.

Ecology: Rocky Mountain maple occurs in old-growth and second-growth forests. It is found in early seral stages, growing within the first 10 years following fire through mature and climax stages. Rocky Mountain maple is a major component or dominant in seral shrub-dominant vegetation, which develops rapidly following disturbance in the northern Rockies. Seral shrubfields result from recurring disturbance including fire and downslope movement of snow, ice, water, and rocks. Rocky Mountain maple is found with a variety of tree species throughout its range, including white fir (Abies concolor), subalpine fir (Abies lasiocarpa), alder (Alnus spp.), birch (Betula spp.), common juniper (Juniperus communis), Rocky Mountain juniper (Juniperus scopulorum), western juniper (Juniperus occidentalis), Engelmann spruce (Picea engelmannii), lodgepole pine (Pinus contorta), limber pine (Pinus flexilis), ponderosa pine (Pinus ponderosa), cottonwood (Populus spp.), quaking aspen (Populus tremuloides), Douglas-fir (Pseudotsuga menziesii), oak (Quercus spp.), and willow (Salix spp.).

In the WFDP: Rocky Mountain maple is very rare in the WFDP, with only one stem above 1 cm at DBH that has been recorded.


Rocky Mountain maple is a native, deciduous tall shrub or small tree. It often grows 6.1-9.1 m tall, with crown widths from 3-6 m wide and a stem diameter up to 30.5 cm, though it can reach 12.2 m tall and 0.6 m in diameter. Rocky Mountain maple has opposite, ascending to erect branches, rounded twigs, and a narrow crown. The bark of Rocky mountain maple is smooth until maturity, when fissures develop.

Habit: Shrub, small tree, < 6 m; dioecious (or staminate plant with some bisexual flowers). Leaf: 3-lobed (or 3 sessile leaflets) 1/4--3/4(1) of leaf length, at least outer side toothed, teeth 3--22, acute to obtuse; abaxial surface pale green, glabrous. Inflorescence: terminal, ascending, flowers 3--8, appearing after leaves. Flower: petals 2--3 mm, +- = sepals. Fruit: wings spreading (0)70--120, rarely touching, parallel.


Fire effects: Rocky Mountain maple has been characterized as fire dependent, and may decline with fire exclusion. Prolific sprouting and wind dispersal of seed of Rocky Mountain maple facilitate rapid revegetation of burned areas. Though top-killed by fire, Rocky Mountain maple generally has low susceptibility to fire due to its ability to survive via sprouting from the root crown. However, after moderate to severe fire, survival of Rocky Mountain maple may be substantially reduced.


Flowering and fruiting - Rocky Mountain maple may be monoecious or dioecious. Flowers are borne in loose terminal cymes arising from lateral buds and grow in drooping clusters. The paired seeds are winged samaras. Seeds are 4-5 mm long and samaras are 20-30 mm long.

Seed dissemination - The mating system of Rocky Mountain maple is dioecious or staminate plants with some bisexual flowers. Rocky Mountain maple likely begins to produce seed before 10 years of age. The large seeds are dispersed by wind, and Rocky Mountain maple often seeds into disturbed areas. Seeds are both animal and wind pollinated.

Vegetative regeneration - Following stem damage or top-kill, Rocky Mountain maple readily sprouts from the root crown. Sprouts may not set seed for 3 years after disturbance.

Species Distribution


USDA Plants Database
USDA, NRCS. 2016. The PLANTS Database. National Plant Data Team, Greensboro, NC 27401-4901 USA.

USFS Plant Database
Habeck, R. J. 1992. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory.

The Jepson Herbarium
The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA. $131.95, hardcover; 1600 pages. ISBN-13: 978-0520253124.

Burke Museum of Natural History and Culture
Burke Museum. 2016. Acer glabrum [Online]. University of Washington.
Photo credit: Bud Kovalchik
Photo credit: Susan McDougall 2009
Photo credit: Clayton J. Antieau 2008