A tree 30 to 65 ft high, of rounded habit, sometimes much smaller or even bushy; branchlets glabrous. Leaves 21⁄2 to 41⁄2 in. wide, somewhat less in length, shallowly five-lobed, heart-shaped at the base, irregularly toothed; dark green, glossy and glabrous above, paler and more or less downy beneath, especially along the chief veins and in their axils, occasionally quite glabrous; lobes angular. Flowers yellow, appearing in March, numerously crowded in short-stalked corymbs; each flower on a slender, glabrous, pendent stalk, 1 to 11⁄2 in. long. Fruit glabrous; keys 1 to 11⁄2 in. long; wings 2⁄5 in. wide, varying considerably in divergence.
Native of S. and Central Europe; introduced in 1752. It is one of the most ornamental of early-flowering trees, producing its blossoms regularly and in great abundance in March and April; they are of a clearer and more pronounced yellow than in most maples. There are several good specimens at Kew, the largest 50 × 6 ft (1965). At Westonbirt there are two off the Broad Drive, 60 × 71⁄2 and 53 × 41⁄2 ft (1966). There is much confusion in the nomenclature of this maple. It is very variable and some authorities have separated the following varieties from it as distinct species:
var. obtusatum (Willd.) Henry A. obtusatum Willd. – Leaves on the whole larger than in the type, and up to 51⁄2 in. wide, the lobes more rounded and the whole under-surface covered with a close down; flower-stalks hairy; fruit-wings not so large as in var. tomentosum. Native of Central and E. Europe. There is an old specimen at Kew 48 ft high, on a trunk measuring 9 ft in girth at 3 ft.
var. tomentosum (Tausch) Rehd. A. opulifolium var. tomentosum Tausch; A. neapolitanum Ten.; A. opalus var. neapolitanum (Ten.) Henry – Leaves up to 6 or 7 in. wide, covered with a pale felt beneath, the lobes quite shallow, especially the basal ones. Flower-stalks hairy, remaining so until the fruits ripen. Native of the country about Naples, where, like the type farther north in Italy, it is largely employed in vineyards as a support on which to train the vines. There is an example of this variety at Westonbirt, off the Broad Drive, measuring 64 × 61⁄2 ft (1966).
From the Supplement (Vol. V)
specimens: Kew, 62 × 63⁄4 ft (1979); St James's Park, London, 41 × 41⁄2 ft (1982); Grayswood Hill, Haslemere, Surrey, 62 × 91⁄4 ft (1982); Westonbirt, Glos., Broad Drive, 75 × 81⁄4 ft (1982) and, Willesley Drive, 80 × 7 ft (1982); Balloan, Castletown, I.o.M., 74 × 101⁄2 ft (1978).
var. obtusatum – The examples at Kew measure 62 × 101⁄4 ft at 3 ft (1984) and 41 × 51⁄4 ft (1980).
var. tomentosum – The tree at Westonbirt measures 68 × 7 ft (1976).
The two above varieties are by some authorities treated as species distinct from A. opalus under the respective names A. obtusatum and A. neapolitanum. They differ clearly enough from typical A. opalus, but it is questionable whether they are really separable from each other.