Description from Flora of China
Acer tegmentosum Maximowicz f. rufinerve A. E. Murray.
Trees to 17 m tall, andromonoecious. Bark smooth. Branchlets green or purplish, glabrous; winter buds ellipsoid, glabrous. Leaves deciduous; petiole 3-4 cm, nearly glabrous; leaf blade ovate or ovate-oblong, 9-13 × ca. 8 cm, papery, abaxially densely rufous pubescent on veins, adaxially glabrous, base subcordate, margin doubly serrulate with adpressed acute teeth, 3-lobed; middle lobes triangular-ovate, apex acuminate; lateral lobes in upper part of blade, much shorter and apex acute. Inflorescence terminal on leafy branchlets, appearing after leaves develop, simple racemose, 6-8 cm, 15-40-flowered. Pedicel ca. 4 mm, slender. Staminate flowers: sepals 5, oblong, glabrous, apex obtuse; petals 5, obovate, apex obtuse; stamens 8, glabrous; disk glabrous, intrastaminal; ovary rudimentary. Samara wing including nutlet 1.4-1.8 cm × 4-6 mm, wings spreading obtusely. Fl. Apr, fr. Aug-Oct.
This species is similar to Acer pectinatum subsp. taronense, but the fruit is much smaller, and the leaves are 3-lobed in the upper part. However, one of us (Chen) believes that the size of the fruit and the number of leaf lobes are variable within taxa of A. sect. Macrantha.
● Mixed forests; 2200-3000 m. NW Yunnan.