A deciduous tree with smooth purplish or brownish to grey young shoots. Leaves three- to five-lobed, but when five-lobed the basal lobes are sometimes very small; blades 3 to 53⁄5 in. long and as much or slightly more wide, lobes triangular to ovate, acuminate to caudate, finely and sharply saw-toothed, often doubly so, the teeth furnished with bristly tips, midrib and veins on the lower surface covered at first with a mealy, rust-coloured indumentum, but later becoming more or less glabrous except in the axils of the nerves at the base. Flowers in spikes. Fruits in compact racemes 23⁄5 to 4 in. long, borne on short pedicels 1⁄/6 to 2⁄5 in. long; keys widespreading (often horizontally), 4⁄5 to 1 in. long, the wings 1⁄5 to 2⁄5 in. wide.
Native of the Himalaya from Nepal eastward, and of Upper Burma (possibly also of Yunnan). It has been much confused with A. papilio (A. caudatum sensu Rehder), from which it is readily distinguished by the fine, bristle-tipped teeth of the leaf-margins, by the mealy, rust-coloured indumentum of the under-surface of the young leaves, and by the racemose inflorescence (in A. papilio the inflorescence is a narrow panicle which becomes racemose only in the fruiting state). A. pectinatum is a little known species, but of considerable interest as the only Himalayan representative of the section Macranthsa, to which the 'snake-bark' maples belong.
Note: Wallich originally gave the name A. pectinatum to Nepal specimens which he catalogued under No. 1226 in the East India Company's Herbarium and also to material collected by Dr Govan at Sirmore. The last is under No. 1225 and is, in fact, A. acuminatum. When he compiled the catalogue, Wallich was of the opinion that A. pectinatum and A. caudatum were distinct species, but when he published the latter he cited A. pectinatum as a synonym and remarked that he had come to regard them as belonging both to one variable species. Nicholson, who validly published the name A. pectinatum Wall, for No. 1226 (Gard. Chron., n.s., Vol. 15, p. 365 (1881)), unfortunately transgressed the Code of Botanical Nomenclature by citing A. acuminatum as a synonym. Pax followed Nicholson in treating A. pectinatum as a distinct species (Bot. Jahrb., Vol. 7, p. 249 (1885-6) and Pflanzenreich, Aceraceae, p. 67 (1902)) and since he did not introduce any extraneous element the name can start from him.
From the Supplement (Vol. V)
This species is now in cultivation and seemingly hardy. It is the senior member of a group of closely related and better-known maples which have been placed under it as subspecies by Edward Murray: A. forrestii, A. laxiflorum, A. maximowiczii, A. taronense; and also the two Formosan maples A. rubescens and A. caudatifolium (kawakamii).