A small tree with glabrous young stems. Leaves membranaceous or somewhat leathery, rather narrowly oblongish-ovate, broadly cordate to rounded at the base, the apex gradually acuminate, prolonged into a tail-like point, 2 to 4 in. long, 11⁄2 to 2 in. wide, margins finely saw-toothed and lobulate or with short lateral lobes near the base, rusty pubescent on the veins beneath at first, later glabrous. Flowers and young fruits usually reddish, borne on long lax racemes; wings of fruits spreading at about a right-angle.
A native of W. China, described by Pax from specimens collected by Pratt near Tatsien-lu (Kating-fu) and by Faber on Mt Omei. The taxonomic boundaries of this species are a matter of dispute and have expanded and contracted according to this or that interpretation. In Plantae Wilsonanae, Vol. 3, p. 426, Rehder placed A. forrestii under A. laxiflorum in synonymy and this judgement, subsequently retracted, was widely accepted and adopted in previous editions of this work. As a result, many trees grown under the label A. laxiflorum are really A. forrestii, now very properly accepted as a distinct species. Secondly, in the first volume of the work cited (p. 94, 1911), Rehder described a variety of A. laxiflorum, namely var. longilobum, differing from the type chiefly in the five-lobed leaves with the veins beneath covered with a dense, yellowish, floccose tomentum. In 1933, however, (Journ. Arn. Arb., Vol. 14) Rehder placed this variety under A. taronense in synonymy, with the exclusion of Wilson's specimen W. 4108 (see below), which he transferred to the typical part of A. laxiflorum. Finally, the maples grown under the collector's number W. 4100 are not this species but fall well within the span of variation of A. maximowiczii. The corresponding herbarium specimen was in fact transferred to A. maximowiczii by Rehder in the article cited above.
With the exclusion of this alien material, A. laxiflorum becomes once again the species that Pax described (though the leaves are occasionally more lobed than in the type specimens). He placed it near to A. davidii, A. hookeri and A. crataegifolium, and it is perhaps most closely allied to the last of these, but differs in the larger, more finely toothed leaves and by the wings of the fruits spreading at about a right-angle (horizontal or widely spreading in A. crataegifolium). From the other two species it differs in its lobulate or slightly lobed leaves. Also, A. hookeri is a quite glabrous species, and A. davidii differs from A. laxiflorum in its much more coarsely toothed leaves, more abruptly acuminate at the apex. There should be no possibility of confusing A. laxiflorum with A. forrestii, which has strongly three-veined and three-lobed leaves, glabrous beneath.
The true A. laxiflorum is rare in cultivation but represented at Trewithen, Cornwall, by two specimens 20 to 25 ft high (1968). These agree well with Pax's original description and figure. In Wilson 4108, as represented in the Edinburgh Botanic Garden, the leaves on the extension growths and young spurs are strongly three-lobed; on older, branched spurs they are less lobed but always strongly three-veined. The difference between this and the Trewithen trees is very striking, but it would appear to belong to A. laxiflorum as at present understood.
A. rubescens Hayata – This rare maple is a native of Formosa (Taiwan), where it inhabits mountain forests at 6,000 to 8,000 ft and grows to 65 ft high; allied to A. laxiflorum; in cultivation at Trewithen from seed collected by Yashiroda some thirty years ago under his No. 109. Its closest ally is A. morrisonense Hayata, another Formosan species, under which it i splaced in synonymy by H. L. Li (Woody Flora of Taiwan, 1963).
From the Supplement (Vol. V)
Of the species mentioned in the taxonomic discussion in the second paragraph, A. forrestii, A. maximowiczii and A. taronense are, like A. laxiflorum, reduced by E. Murray to the rank of subspecies of the Himalayan A. pectinatum.
A. rubescens – This species is now well-established in cultivation, and moderately hardy. The tree at Trewithen in Cornwall measures 60 × 6 ft (1985).
† A. caudatifolium Hayata A. kawakamii Koidz.;? A. morrisonense Hayata – This species, like A. rubescens a native of Formosa (Taiwan), was introduced to cultivation by Gordon Harris in 1971. The leaves are unlobed or shortly three-lobed, slenderly tapered at the apex. In A. rubescens the leaves are shortly five-lobed. The two species are united by E. Murray and placed under A. pectinatum as subsp. formosanum.