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A deciduous tree to 17 m in the wild. Bark dark green with pale stripes. Branchlets glabrous, greenish to purplish red, faintly striped white. Buds stipitate, small, ellipsoid, glabrous, with two pairs of valvate scales. Leaves ovate, chartaceous, base cordate to subcordate, unlobed to three-lobed, 7–12 × 5–9 cm, central lobe ovate, triangular-ovate, apex caudate-acuminate, lateral lobes triangular-ovate, apex acuminate; margins double-serrulate, teeth adpressed, upper surface dark green, lower surface paler, glaucescent, with pubescent vein axils; petiole 2.5–5 cm long, red or green, grooved, glabrous or pubescent; autumn colours yellow to red. Inflorescence terminal, racemose, pendulous, 5–20 flowered. Flowers yellowish green, 5-merous, pedicels slender, 0.6–0.8 cm long, sepals oblong, ~0.3 cm long, petals obovate, 0.3–0.4 cm long, stamens eight, inserted outside the nectar disc. Samaras 2.3–2.5 cm long, wings narrowly spreading. Flowering May, fruiting October. (Fang 1939; Xu et al. 2008).
Distribution China South western Sichuan, North western Yunnan
Habitat Temperate mixed forests and valleys between 3000 and 3800 m.
USDA Hardiness Zone 6-7
RHS Hardiness Rating H6
Conservation status Least concern (LC)
The taxonomic position of Acer forrestii has long been a source of debate among Acerologists. Introduced by Forrest from Yunnan in 1906, and described from his material, it was reduced to the synonymy of A. laxiflorum by Rehder in 1917 (Sargent 1917), then resurrected as a species by the same author in 1933 (Rehder 1933), this treatment upheld by Fang (1939) in his monograph of Chinese maples.
Confusingly, in his account of the species and in relation to A. laxiflorum, Bean (1976) states that ‘There seems to be no other reliable character by which they may be distinguished..’, while in the account of Acer laxiflorum writes that ‘there should be no possibility of confusing A. laxiflorum with A. forrestii, which has strongly three-veined and three-lobed leaves, glabrous beneath.’ While this identification feature is useful, it is too much of a sweeping statement by far, as all manner of intermediates between the two can be found, sometimes on the same plant. Rehder (1933) considered characters of pubescence on lower leaf surfaces in A. laxiflorum and glaucescent undersides in A. forrestii as the most useful way to split the two, though these characters do not always correlate with one another.
van Gelderen, de Jong and Oterdoom (1994) treated Acer forrestii and A. laxiflorum as different entities, though as subspecies of A. pectinatum, a treatment first proposed by Murray (1977) and since rejected by Xu et al. (2008). Though, given the intermediate forms between the two species, in both leaf and flower number, while it would be rash to jump to any conclusions without the benefit of a comprehensive molecular study, it is reasonable to suggest that this so-called species might sit better within A. laxiflorum, as Rehder had indeed earlier considered (Sargent (1917).
Less debatable is that plants of the Acer forrestii affinity are of great ornamental value. While its autumn colour is unspectacular, its appearance in high summer is anything but. Vibrant red fruits contrast with bright green leaves most effectively. This said, not all examples exhibit this feature, with some origins producing fruit that remains largely green. Among the best red fruited specimens are those of ACE 2066, ACE 2076 and CLARKE 4200, the former collected in the Habashan area of Yunnan. All grow at Hergest Croft, while a plant from ACE 2066 is one of the best for the time of year for any tree at Westonbirt, The National Arboretum. Growing in Silk Wood, the neighbouring OGISU 95093 is also notable for this character. A second plant of ACE 2066 has been added to the Westonbirt collection, acquired from Windsor Great Park, who had propagated plants of it on instruction from the late Mark Flanagan, shortly before his untimely death in 2015. While leaf lobing is not a consistent feature of these plants, particularly on fruiting branches, the greater number of fruits and their glaucous leaf undersides distinguish them from A. laxiflorum (sensu Xu et al. 2008). This applies also to SICH 1461, which forms a broad spreading tree with arching branches on a single stem at Westonbirt.
A native of Upper Burma and neighbouring parts of Yunnan and Tibet; discovered by Kingdon Ward in 1914; introduced by Forrest. It is a tender and little-known maple, more at home in section Macrantha with the snake-bark maples than near A. sinense, which Sir William Wright-Smith suggested as its nearest ally. The fine specimen at Trewithen, Cornwall, died recently from the effects of the 1962-3 winter but we are told by Mrs Johnstone that one cutting from it was struck.