Acer oblongum DC.

(Sect. Palmata, Sect. Penninervia)

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Bean

New Trees

A sub-evergreen or deciduous tree, found both in the Himalaya and China. In the Himalaya it grows 50 ft in height, but plants from that region are too tender for our climate. In China it appears to be most frequently 20 to 25 ft high. It is a tree without down; the leaves hard and leathery in texture, normally oblong or oblong-ovate, 2 to 4 in. long, 34 to 112 in. wide; pointed at the apex, tapered or rounded at the base, normally neither lobed nor toothed; distinctly glaucous beneath. In the Himalayan form the leaves may be up to 6 or 7 in. long. Flowers in downy panicles. Fruits glabrous; keys about 1 in. long; the wings about 14 in. wide.

Native of the Himalaya, W. and S. China; an allied species is found in Formosa. This species is variable in leaf; the venation may be quite pinnate or become three-veined by the proportionately stronger development of the basal pair of lateral veins. Young plants often bear distinctly three-lobed, sharply toothed leaves as well as the normal ones. Three-lobed leaves may also occur on adult trees and it was such a one that furnished the type of Henry's var. trilobum, but this condition seems to be part of the normal variation of the species.

A. oblongum was introduced from the Himalaya in 1824 and a hardier form by Wilson in 1901. A tree at Kew from this seed died, but another, bought from Veitch in 1908, and almost certainly also from Wilson seed, proved hardy and is now 22 ft high (1960).

var. concolor Pax – Leaves green on both sides.

var. latialatum Pax – Wings of fruit broad, 12 in. wide, and almost semi­circular. Described from a tree that once grew in the Botanic Garden, Florence, but reported from the wild.

A. paxii Franch. A. oblongum var. biauritum W. W. Sm. – Rehder concluded that this species is no more than a variety of A. oblongum and identified it with var. biauritum, founded on a specimen collected by Forrest in Yunnan. Fang, in his Monograph on the Chinese Aceraceae, agrees that they are identical but retains A. paxii as an independent species. It bears evergreen leaves, which are sometimes quite entire, but just as commonly three-lobed, and the two kinds of leaf may appear together on the same shoot. The lobes, sometimes no more than large teeth, are borne about midway up the leaf, which is broadly ovate to halberd-shaped, and up to about 212 in. long, 135 in. wide. The inflorescence is a corymbose panicle, as in A. oblongum. However, specimens of A. paxii in the Kew Herbarium have glabrous inflorescence branches (downy in the other species) and also show the following further marks of difference: A. paxii has longer petals and the nutlets of the fruit are rounded, while in A. oblongum they are more angular.

A. paxii was discovered by Père Delavay in Yunnan and is distributed over much of S. China. A plant grown at Kew under this name has survived recent hard winters but does not thrive. It agrees with A. paxii in its foliage, but in the absence of flower and fruit it cannot be identified with certainty.

A. buergerianum, at least in the normal wild form, resembles A. paxii in its polymorphic leaves, but these are deciduous.


From the Supplement (Vol. V)

In addition to A. paxii, there are other allies of A. oblongum in China and Formosa (Taiwan). Those introduced by Gordon Harris are A. albo-purpurascens Hayata of Formosa; A. cinnamomifolium Hayata from eastern China; and A. lanceolatum Molliard from Hong Kong. All these have proved tender.

From New Trees

Acer oblongum DC.

(Sect. Palmata, Ser. Penninervia)

Flying Moth Maple

This species was described by Bean (B215, S49) and Krüssmann (K86). It is in general rather tender, but is valued as a street tree in Mediterranean Europe and southern California (le Hardÿ de Beaulieu 2003). Six varieties are recognised in addition to var. oblongum; of these, two (var. concolor and var. latialatum) were discussed by Bean, and a third, var. itoanum, has recently come into cultivation.

Seedlings attributed to A. oblongum var. concolor Pax (see Bean: B215) have been offered commercially, from a collection made in Vietnam in 2003 (HWJ 3869). The parent trees had a very striking white glaucous underside to their leaves (Heronswood Nursery catalogue 2005), which should make these very interesting specimens to watch. Dan Hinkley (pers. comm. 2007) reported that individuals in his garden in coastal Washington had been defoliated by frosts of –8 ºC in the winter of 2006– 2007, but that they were budding out in the spring. Young plants seen at Crûg Farm, Gwynedd in 2007 had rather large leaves, and their identification should perhaps be revisited in future.

Acer oblongum var. itoanum (Hayata) H.L. Li

Var. itoanum differs from typical A. oblongum in its slightly smaller leaves (4.5–10 × 2–5 cm) with wavy margins, and its somewhat isolated distribution. Van Gelderen et al. 1994. Distribution JAPAN: Ryukyu Is. Habitat Subtropical evergreen forests between 1000 and 1700 m asl. USDA Hardiness Zone 9–10. Conservation status Not evaluated. Illustration NT75.

The only large specimen of Acer oblongum var. itoanum seen in the research for the current work grows at Quarryhill, where it was 3.5 m in 2004. The leaves of this individual vary from simple to trilobed or irregular in shape, and are dull dark green in colour. Perhaps because it is planted in a comparatively open spot, its foliage is apt to be sun-scorched, and the shoot tips can be damaged by frost; a site under a high canopy might be more favourable. This tree is a survivor from a batch of seedlings raised from the 1992 Index Seminum of Chiba University, Japan, the rest having succumbed to Armillaria (W. McNamara, pers. comm. 2004; H. Higson, pers. comm. 2007). There is a young plant still in the nursery at Kew, donated by Makino Botanical Garden, Japan.

Genus

Acer

Other species in the genus