- Deciduous tree, 50-75(100) ft [15-23(30) m], ascending, becoming rounded, shallow root system. Leaves, opposite, simple, large (20-30 cm across, the largest leaves of all the maples), lustrous dark green above, pale beneath, 3-5 toothed lobes, petiole yields milky sap when detached. Flowers in early spring usually before leaves appear, the flowers are small, 10 mm across, greenish-yellow, fragrant, in drooping clusters, 10-15 cm long, male and female flowers occur in the same cluster. Fruit (double samara), large, 4 cm long, hang down in racemes, seeds very pubescent. Foliage yellow to gold or brown in fall.
- Sun to part spade. Prefers a cool moist environment as that in the Pacific Northwest.
- Hardy to USDA Zone (5)6 Native from southwest British Columbia to southern California, from sea level to 5,500 ft (1,650 m).
- Because the bark of this tree retains moisture, in the Pacific Northwest its trunk and large branches are often covered with mosses, liverworts, and ferns (especially the licorice fern, Polypodium glycyrrhiza). Its sap has a high sugar content, but early spring weather in its range is generally not conducive to a high flow of sap. When cut down, the remaining stumps sprout vigorously, growing over 3 m in a single year.
- A few forms have been identified and named, but are not generally found commercially, these include, Acer macrophyllum var. rubrum, the new leaves of this form are reddish and contrast with the yellow flowers; Kimballiae which has more deeply lobed leaves and Seattle Sentinel, an upright (fastigiate) form.
- macrophyllum: macro, large; phyllon, a leaf.
- Oregon State Univ. campus: large tree NW of Pharmacy.