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A deciduous tree to 20 m in the wild. Bark dark green with pale stripes, soon turning brown with age. Branchlets glabrous, purplish green. Buds stipitate, ovoid, with two pairs of valvate scales, purplish. Leaves suborbicular, base strongly cordate to subcordate, three- or five-lobed, 7–10 × 6–8 cm, central lobes ovate, apex caudate-acuminate, lateral lobes triangular, apex obtuse to caudate-acuminate, margins finely serrate, upper surface matt green, lower surface pale green, with reddish to rusty pubescence at least at first, persisting along veins; petiole 2–7 cm long, red, grooved, glabrous or rusty pubescent, at least at first; autumn colours yellow to orange. Inflorescence terminal, racemose, pendulous, 10–40 flowered, 6–8 cm long. Flowers purplish green, 5-merous, pedicels slender, 0.5–0.7 cm long, sepals oblong, ~0.5 cm long, petals obovate, ~0.8 cm long, stamens eight, inserted outside the nectar disc. Samaras 1.3–1.8 cm long, wings spreading obtusely or more broadly. Flowering May, after the leaves have emerged, fruiting October. (van Gelderen, de Jong and Oterdoom 1994; Xu et al. 2008).
Distribution Bhutan Myanmar China Southern Xizang, North western Yunnan India Nepal
Habitat Temperate mixed forests between 2500 and 3700 m.
USDA Hardiness Zone 6-7
RHS Hardiness Rating H5
Conservation status Least concern (LC)
The Acer pectinatum complex is one of the most debated complexes in the genus Acer, let alone section Macrantha. It is broadly considered to include six named taxa, as well as another, insufficiently circumscribed taxon. The named taxa, as treated by Xu et al. (2008) and here, are: A. chienii, A. forrestii, A. laxiflorum, A. maximowiczii, A. pectinatum subsp. pectinatum and subsp. taronense. Treated as a single species, A. pectinatum, comprising 5 subspecies (A. chienii is treated in the synonymy of subsp. taronense by van Gelderen et al. (1994).
The complex can be split in two by bark characters, with that of Acer forrestii, A. laxiflorum and A. maximowiczii remaining green after many years, while that of the remaining taxa turns quickly brown, losing their snakebark effect, though remaining valuable from an ornamental perspective. A.chienii can be separated from A. pectinatum sensu Xu et al. (2008) by its lobes, where present, initiating from the upper half of the leaf. In A. pectinatum, these are always present and derive from the lower half. Distinguishing the subspecies within A. pectinatum sensuXu et al. (2008) can be somewhat tricky, with the most useful character seemingly the presence of absence of pubescence along the petiole, the nominate subspecies being glabrous in this regard. Both taxa within the species are distinctly pubescent on their leaf undersides, at least along veins and often throughout at first, if not later. Xu et al. (2008) describe subsp. taronense as the more hirsute of the two.
The typical subspecies was observed as a common forest feature in parts of Nepal by Roy Lancaster (Lancaster 1981), who, as part of the team of Beer, Lancaster and Morris (BL & M) also introduced seed of this species. Whether or not the UK and Irish Champion, standing at 14.5 m in 2014 (The Tree Register 2019) at Westonbirt, The National Arboretum was grown from this source can only be speculated. SCHL 2247, also from Nepal, grows at Yorkshire Arboretum and measured 9 m tall in 2009 (The Tree Register 2019).
The as yet unsatisfactorily characterised taxon within the complex is the snakebark that which has been introduced from Fan Si Pan, northern Vietnam, in recent years, and fast becoming the most represented member of the complex in cultivation. It forms a stunning tree of upright form with bronze new growth and yellow autumn colour. Collections include those made by Sue and Bleddyn Wynn Jones and Dan Hinkley, such as BSWJ 8270 and HWJ 569 (both from the same tree near a campsite on Fan Si Pan at 2700 m (Grimshaw and Bayton 2009), as well as Keith Rushforth collections under KR 3012 and KR 3031. This entity also occurs over the Chinese border in southern Yunnan. More recent collections in section Macrantha from the region made under the VIET code should not be confused with this taxon, as these represent an entity closer to A. davidii than to A. pectinatum.
The name and identification of this material has become more confused than most, with material introduced under the name of Acer campbellii var. fansipanense. Confusing particularly because Acer campbellii belongs to section Palmata, rather than section Macrantha, this error can be traced back to Gagnepain, who described the taxon, though with the slightly different spelling, fantsipanense (Gagnepain 1948). Study of the type material at VHM in Ho Chi Min City revealed that while Gagnepain attributed this taxon to A. campbellii the material his description referred to in fact belongs to section Macrantha (Crowley 2018). The publication of its name was however invalid, on account of the protologue being written in French, rather than Latin (Gagnepain 1948). It appears that those who attributed the name of Acer campbellii var. fansipanense were likely following Pham (1992) whose documentation of the Vietnamese flora includes the description and illustration of this material using this variant spelling. Though it has also been observed growing as Acer fansipansensis, this combination has not been published. Now available in the trade as Acer pectinatum subsp. pectinatum (Crûg Farm Plants 2018), at this point A. aff. pectinatum is more appropriate. While it may be included within this species, its characters fit neither of the subspecies as circumscribed by Xu et al. (2008) and requires a name. It differs from these in its often more strongly five-lobed leaves, which are largely glabrous except for tufts in its basal axils. Fine examples include those at Hergest Croft, Herefordshire and Westonbirt.