Kindly sponsored by
Dan Crowley (2020)
Crowley, D. (2020), 'Acer pensylvanicum' from the website Trees and Shrubs Online (treesandshrubsonline.
A deciduous shrub or tree to 12 (–15) m. Bark dark greenish-brown to reddish-brown with pale stripes. Branchlets glabrous, greenish-yellow, striped white. Buds green to red, stipitate, ovoid to ellipsoid, with 2 pairs of valvate scales. Leaves obovate, base cordate to rounded, shallowly 3-lobed, lobes ovate, 8–16 × 10–18 cm, central lobe broadly triangular, apex acuminate, lateral lobes smaller, margins finely serrate, upper surface matt green, lower surface pale green, with reddish to rusty pubescence at first, petiole 6–12 cm long, green, grooved; autumn colours yellow to golden. Inflorescence terminal, racemose, pendulous, usually dioecious, 12–20 flowered, ~12 cm long. Flowers yellowish-green, 5-merous, pedicels slender, 0.6–1.3 cm long, sepals obovate, ~0.6 cm long, petals narrowly obovate, slightly longer than sepals, stamens 7 to 8, inserted outside the nectar disc. Samaras 1.8–2.5 cm long, wings spreading at acute angles or broadly spreading; nutlets nearly flattened, concave on one side. Flowering from May to June, emerging after the leaves, fruiting in October. (Sargent 1965; Elias 1980; Rushforth 1999; van Gelderen & van Gelderen 1999).
Distribution Canada Prince Edward Island, New Brunswick, Nova Scotia, southern Ontario, southern Quebec United States Connecticut, Georgia, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia
Habitat Moist woodlands between 0 and 1000 m.
USDA Hardiness Zone 6-7
RHS Hardiness Rating H6
Conservation status Least concern (LC)
An understorey component of the deciduous forests of eastern North America, Acer pensylvanicum was introduced to Europe in 1755 (van Gelderen et al. 1994), two years after being described by Linnaeus. In his protologue he only included a single ‘n’ in the specific epithet, hence the difference in spelling from Pennsylvania, for which it is named. It is the North American disjunct of section Macrantha, being the only member of the section to be found growing wild outside of eastern Asia and unsurprisingly, was the first to be introduced to European collections (Bean 1976a).
The species is well represented in our area from collections made across its range, though is less frequent than many of its Asian relatives. Described by Bean (1976a) as one of ‘the most desirable of maples’ and though its cold-hardiness is undisputed, it does not perform well everywhere. It is a true understorey species and does not tolerate full sun. Dirr (2011, p. 45) writing with a southeastern United States bias, imparts that ‘the vagaries of the domesticated environments often wreak havoc’ on it, advocating the use of other snakebarks over this species, including A. tegmentosum. The white barked forms of that species are perhaps rivalled for the most spectacular bark of the snakebarks by those of A. pensylvanicum, which turn vibrant red in winter and for which various cultivars have been named. In autumn its leaves, the largest of all in the section, turn a brilliant yellow.
As well as some named selections, hybrids involving A. pensylvanicum may be found growing in collections named as this species. An old, sizeable tree at Westonbirt, formerly designated champion status on account of its label, appears to be a hybrid. As well as its vigour and longevity, its location, around 1 m away from a mature oak tree, suggests a seedling origin. Seedlings from plants grown in collections should be identified with caution.
In leaf characters, A. pensylvanicum is often compared with A. rufinerve, but the leaves of the latter are usually rather smaller, while the Japanese species also has prominently bloomed shoots and rounded nutlets. A. tegmentosum also bears some resemblance, though this too also has bloomed shoots and leaves often with prominent basal lobes, appearing orbicular, rather than obovate in outline. The common name of moosewood relates to the species’ attractiveness to deer, caribou and moose as browsing material (Jacobson 1996).
Synonyms / alternative names
Acer pensylvanicum 'Red Snake'
RHS Hardiness Rating: H6
Introduced by Späth’s nurseries, Berlin, in 1904 (Bean 1976a). It has upright branching and bark that turns from a dull green in summer to salmon pink or red, with pale striations, in winter. Its leaves are slightly smaller than is typical of the species and are a paler green, turning yellow in autumn. It is difficult to propagate, even through grafting onto typical Acer pensylvanicum (van Gelderen & van Gelderen 1999). Jacobson (1996) noted that it was ‘exceedingly rare in North America’.