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A deciduous tree to 25 m in the wild. Bark pale brown to yellowish grey. Branchlets glabrous, lenticillate, turning grey to brown and woody by the end of the first year. Buds ovoid, with five to eight pairs of imbricate scales. Leaves pentagonal in outline, base subcordate to rounded, (three-) five to seven (-nine) lobed, (6-)7–13 × (6-)10–20 cm, margins entire, lobes triangular to ovate, apically acuminate, upper surface mid green, lower surface pale green, glabrous or pubescent; petiole 4–20 cm long, slender, glabrous, exuding milky sap when broken; autumn colour yellow to red. Inflorescence terminal, corymbose-paniculate, glabrous, many flowered. Flowers red to yellowish green, 5-merous, usually andromonoecious, sepals oblong, 0.2–0.8 cm long, petals elliptic to obovate, as long, or shorter, than sepals, stamens eight, inserted in the middle or on outside of the nectar disc. Samaras yellow to red, 3-3.5 cm long, wings spreading variously, nutlets flattened. Flowering April to May, appearing before or with unfolding leaves, fruiting September to October. (Krüssmann 1984; Ogata 1999; van Gelderen et al. 1994; Xu et al. 2008).
Distribution China Zhejiang, Yunnan, Xizang, Sichuan, Shanxi, Shaanxi, Nei Mongol, Anhui, Gansu, Hebei, Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jilin, Liaoning Japan North Korea South Korea Mongolia Russia Vietnam
Habitat Mixed temperate forests from zero to 3300 m asl.
USDA Hardiness Zone 5-6
RHS Hardiness Rating H6
Conservation status Least concern (LC)
Taxonomic note The name Acer pictum and its correct usage has been much debated and the complexity of the issue laid out by Wijnands in van Gelderen et al. (1994), who argued for the use of A. mono, a name based on Japanese material which has been much used in horticulture and botanical texts, including van Gelderen et al. (1994), largely on account of A. pictum being used as the basionym of Kalopanax pictus (now K. septemlobus), a member of the Araliaceae. However, when a formal proposal to reject the name A. pictum was made (Wijnands 1990), this was rejected seemingly on the basis that the name was not used widely and persistently enough to be rejected under the grounds on which the rejection was proposed, and the use of this name endorsed (Brummitt 1993). A second proposal (van Rijckevorsel 2008) was also rejected because by this point the name A. pictum was widely used, including in several significant regional floras (Brummitt 2011).
Relatively well-known and grown, Acer pictum was previously described by numerous authors, including Bean (1976a) and van Gelderen et al. (1994) as Acer mono (see taxonomic note for further details), a name it is often still found growing under. It may also be found growing under A. cappadocicum as the two can be similar in leaf but are easily separated by characters of the branchlets. In A. pictum (and relatives), these are brown by the end of the first growing season. In A. cappadocicum (and its relatives), these remain green and photosynthetic for several years. Various leaf forms are seen in A. pictum and several of the described lower taxa are represented in cultivation. Of the total of ten subspecies treated in respective floras of China and Japan (Ogata 1999; Xu et al. 2008), seven are recorded in collections (glaucum, pubigerum and tricuspis are those not noted as present). These include a number of wild sourced introductions from both these countries, as well as Korea. In a widespread and complex group such as this it should come as no surprise that the identity of some of this material has been confused. Discussions pertaining to the correct identity of some recent introductions may be found in the various infraspecific accounts. As with many other species complexes within Acer quite how the establsihed classification of lower taxa will stand up to molecular study remains to be seen. A tentative key to the subspecies currently recorded in gardens is presented below.
Bean (1976a) states that the species was first introduced to Britain from Japan by Maries in 1881, and from China by Ernest Wilson in 1901, sometime after it had been introduced to Russia. The original introduction to Western cultivation is reportedly that of Siebold, however, who introduced it to the Netherlands in 1860, while W.S. Bigelow sent material from Japan to the Arnold Arboretum, Boston, in 1891 (Jacobson 1996). Unsurprisingly, the species is somewhat variable in form as well as in leaf and while its autumn colour is usually yellow, it can ocassionally be a good red. A young tree at the Morris Arboretum, Philadelphia, is notable in this regard. The species has also given rise to a number of cultivars, though it does not appear to have the popularity of some of its relatives in section Platanoidea.
Mature leaves with lower surfaces pubescent, pubescence not restricted to veins or axils
Mature leaves with lower leaf surfaces glabrous, or pubescent only along veins or in axils
Leaves with upper surfaces glabrous throughout
Leaves with upper surfaces pubescent along primary veins
Leaves (three-) five (seven)-lobed
Leaves (five-) seven to nine-lobed
Lobes dissected to more than halfway
Lobes dissected to less than halfway
Fruits spreading horizontally, or nearly so
Fruits spreading obtusely, or to a 90° angle
Leaves five to seven -lobed, with lower surface glabrous or along veins
Leaves seven to nine -lobed, lower surface with pubescence only in basal vein axils
Subsp. macropterum has three- to five-lobed leaves with truncate bases that are pubescent or not beneath. The samaras are 3–4 cm long with wings spreading horizontally. Xu et al. 2008.
RHS Hardiness Rating: H4
The identity of representatives of subsp. macropterum have been somewhat confused in collections. It is known in cultivation from two collections, SICH 1814, collected in Nanjiang County, Sichuan in 1996 and SICH 2087, also collected in Nanjiang County, in 1999. Both have been found in collections under names A. cappadocicum subsp. sinicum and A. longipes. The former grows well at Wakehurst, West Sussex and Westonbirt Arboretum, Gloucestershire, where it has made an attactive tree with a rounded crown. Interesting variation has been found within seedlings of SICH 2087, with some, though far from all specimens, taking a fastigiate form. Examples grow at Hergest Croft, Herefordshire and RBG Kew. In both examples, red developing fruits contrast very satisfactorily with the green foliage.
Similar in leaf form to Acer truncatum, A. pictum subsp. macropterum can be distinguished from that species in its fruits with wings more than twice as long as the nutlet. A collection of A. pictum from Seo My Ty, northern Vietnam, made by Dan Hinkley in 2006 appears, in leaf and flower, closest to this subspecies. This collection represents an extension of the range of A. pictum, not previously recorded from Vietnam, though the habitat in which this collection was made has since been destroyed. Though recorded as A. pictum subsp. macropterum in Grimshaw and Bayton (2009), SICH 1107 belongs to A. cappadocicum subsp. sinicum rather than to this taxon.
This subspecies has five- to seven-lobed leaves, 12–15 cm across with entire margins, and samaras 3.5–4.5 cm long with converging wings. Van Gelderen et al. 1994. Distribution SOUTH KOREA: Ullung-do. Habitat Forest remnants. USDA Hardiness Zone 6–7. Conservation status Not evaluated. Illustration NT99, NT100.
Rarity has added piquancy to the interest in this taxon, but fortunately it would seem that the report of only 15 surviving specimens (van Gelderen et al. 1994) is an underestimate, as Kirkham & Flanagan (2005) record it as a principal constituent of woodland they visited in South Korea in 1989. There, on the island of Ullung-do, it is a large tree up to 20 m tall, with wide-spreading branches. Seed from this expedition (KFBX 168) has given rise to a very vigorous specimen at Kew, 8 m tall in 2005 (Flanagan & Kirkham 2005), but there are several other large specimens in the United Kingdom as well, including one that was 9 m tall when measured by Owen Johnson for TROBI in 2003, at Batsford Park, Gloucestershire, and one that has reached 10 m at Hergest Croft (planted in 1985). The Hergest Croft tree is a fine individual with ascending branches, although it is prone to depredations by squirrels. Another large specimen (9–10 m) grows at Chevithorne Barton in Devon. Both of the latter trees are derived from a collection made in 1982 by James Harris and Joe Witt, from which only two seeds germinated (J. Harris, pers. comm. 2006). Viable seed is now produced in cultivation. In North America it is growing at the Arnold Arboretum and elsewhere. At the David C. Lam Asian Garden, a 12 m tall tree, grown from seed collected by Ferris Miller in 1980, has an 18 m spread of branches; Peter Wharton commented that it is ‘very, very vigorous’ (pers. comm. 2007). It is not fully hardy in Poland (P. Banaszczak, pers. comm. 2007).
The leaves of all the A. pictum subsp. okamotoanum seen have had an elegant poise with upturned lobe tips, enhanced by a slightly undulate margin. They emerge light red and turn a good yellow in autumn. It grows very well on alkaline soils (J. Harris, pers. comm. 2007).