A deciduous tree 30 to 50 ft high, with the younger bark green or purplish red becoming striped with white. Leaves glossy green, ovate, slightly heart-shaped at the base, unevenly toothed, 3 to 7 in. long, 11⁄2 to 4 in. wide; veins prominent and parallel; covered with reddish down when young, each vein enlarging at the base where it joins the midrib and forming a minute pocket. Flowers yellowish, on slender, pendulous racemes 11⁄2 to 21⁄2 in. long, the female flowers on longer stalks and larger racemes than the males. Fruit glabrous; keys 11⁄4 in. long; wings 3⁄8 in. wide, spreading almost horizontally.
Native of China; described in 1888, but Maries had introduced it for Veitch in 1879 from the Ichang area, W. Hupeh; Wilson collected seed in the same locality in 1902 and later in other parts of Hupeh and Szechwan. A. davidii has a wide range in China and it was later introduced from further south, in Yunnan, by Forrest and Kingdon Ward. Two very distinct forms of A. davidii are grown in the Edinburgh Botanic Garden. One is of compact habit; the branches have short internodes, about 21⁄2 in. long, and the leaves are up to 41⁄2 in. long and 3 in. wide. This represents the Maries-Wilson provenance. The other tree derives from seed collected by Forrest in Yunnan; this is of loose open habit; the branches have internodes up to 4 in. long and the leaves are larger than in the other tree, being up to 71⁄2 in. long by 5 in. wide (Baileya, Vol. 5, 1957, p. 141). The second tree is also distinct in its purplish young stems. This Forrest introduction is also represented at Kew and Westonbirt, and is sometimes seen in collections under the label “A. forrestii”. The confusion apparently arose through seeds and plants of this form having been distributed in error under the field number F. 22239, which properly belongs to an introduction of the true A. forrestii.
Although the leaves of A. davidii are normally quite unlobed, forms with small lobes near the base are represented in the Kew Herbarium; certainly on some cultivated trees a certain lobing is discernible. On the other hand, in the allied A. grosseri the usual lobes are sometimes absent or poorly developed. In that species, however, the leaf-margins are more finely toothed than in A. davidii and the leaves relatively wider, being roundish-ovate and almost as broad as long.
This interesting species is well represented at Westonbirt by specimens up to 48 ft high. The fine example near the junction of Mitchell and Morley Drives appears to be of the Maries or Wilson provenance: it has yellowish-green leaves which are folded upward along the line of the midrib, and a dense, rounded crown. It is strikingly distinct from the tree in the Nursery at Westonbirt which has flat, longer, more tapered leaves and a narrower and laxer habit. This is probably from Forrest's seed. At Kew there is a beautiful specimen, planted in 1923, received under the number F. 22239 (see above). This is in the Acer collection. Here, and at the western end of the Cedar Vista (near the Lake), there are trees raised from McLaren 250, with sparse, elegantly arching branches; others, from this number and from Yü 15041, are in the Acer collection, and there are similar specimens at Westonbirt. This beautiful form of A. davidii has acquired the misleading cultivar name 'Horizontale', which is likely to cause confusion with the botanical var. horizontale, described by Pax from a specimen collected in Shensi and distinguished from the type by the horizontally spreading fruit-wings. This variety was considered by Rehder to belong to A. grosseri.
From the Supplement (Vol. V)
This species, in its botanical characters, is very near to the earlier-named A. hookeri, and in a monographic treatment would probably come under it as a subspecies. From a horticultural standpoint however, they are distinct, A. davidii being a valuable hardy garden tree, while A. hookeri is tender. E. Murray in effect unites them, placing both under A. sikkimense subsp. davidii (Franch.) Wesm. For A. sikkimense, see this supplement under A. hookeri.
specimens: Kew, by Tea Bar, 39 × 41⁄4 ft (1975); R.H.S. Garden, Wisley, on Battleston Hill, 31 × 41⁄2 ft (1978); Savill Garden, Windsor Great Park, a many-stemmed tree 52 ft high; Winkworth Arboretum, Surrey, 41 × 41⁄2 ft (1980), 62 × 41⁄2 ft at 2 ft and 50 × 41⁄2 ft at 2 ft (1983); Leonardslee, Sussex, 52 × 41⁄4 ft (1985); Wakehurst Place, Sussex, Species Beds, 46 × 33⁄4 ft (1979), Golf Ground Extension, 35 × 5 ft (1981); Abbey Garden, Bury St Edmunds, 42 × 43⁄4 ft and 36 × 43⁄4 ft (1984); University Botanic Garden, Cambridge, 35 × 33⁄4 ft + 3 ft (1982); Westonbirt, Glos., junction of Mitchell Drive and Main Avenue, 46 × 31⁄4 ft and, in The Waste, 42 × 31⁄2 ft (1981); Trewithen, Cornwall, 46 × 5 ft (1985); Dyffryn, near Cardiff, 46 × 41⁄4 ft (1979); Bodnant, Gwyn., 36 × 4 ft (1984); Birr Castle, Co. Offaly, Eire, 46 × 33⁄4 ft (1985).
There were two reintroductions of A. davidii in 1981, from widely separated areas: Lancaster 962 from near Liuba in the foothills of the Minya Konka range in western Szechwan; and by the Sino-British Expedition to Yunnan (SBEC 466).
† cv. 'Serpentine'. – A selection raised from seed in Holland, apparently from Forrest's form, with smaller leaves than normal. Young wood brown.