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A deciduous tree over 100 ft high in a wild state, with a trunk 9 to 12 ft in girth, forming a shapely rounded head of branches; branchlets glabrous. Leaves palmate, usually five-lobed, heart-shaped at the base, 4 to 6 in. wide; always downy in the axils of the chief veins beneath, but varying in different trees from glabrous to downy in other parts. Flowers without petals, greenish yellow, produced in clusters, each flower on a thread-like, hairy stalk more than 2 in. long. Fruit glabrous, wings 1 in. long, 3⁄8 in. wide.
Native of eastern N. America; introduced, according to Aiton, in 1735, but not many fine specimens are to be found in this country. The most notable arc in the Westonbirt collection, the finest there, and perhaps in the country, being in the Park, near the lodge, measuring 80 × 8 ft (1966). Others at Westonbirt are: Willesley Drive 70 × 43⁄4 ft; Circular Drive 63 × 53⁄4 and 65 × 43⁄4 ft (1966). In the grounds of Blenheim Palace, Oxon., there is a tree of 64 × 51⁄4 ft (1965). In Ireland the best recorded is at Mount Usher, Co. Wicklow, Eire, 62 × 71⁄4 ft (1966). In leaf, the sugar maple, especially in its more glabrous form, bears some resemblance to the Norway maple; but the sap of the sugar maple is watery, not milky as in the other.
The famous maple sugar of N. America is obtained almost solely from the sap of this tree. The State of Massachusetts alone used to supply more than half a million pounds annually. It is obtained by tapping the trees and collecting the juice, which is afterwards evaporated. As an ornamental tree in England this maple never seems to have been a great success, and although it appears to be quite hardy, does not grow quickly when young. In streets, and isolated in the meadows of New England, it is magnificent, and forms one of the chief elements in the glorious colour effects of autumn there, its leaves dying off into various shades of orange, gold, scarlet, and crimson, each tree, according to Emerson, retaining year after year its particular shades.
specimens: Hackwood Park, Hants, 80 × 81⁄2 ft (1977); Belton Park, Lincs., 68 × 8 ft (1978); Blenheim Palace, Oxon., 62 × 61⁄4 ft (1978); Bulstrode Park, Oxon., 90 × 11 ft (1967); Westonbirt, Glos., Willesley Drive, 88 × 51⁄2 ft, Broad Drive (NW), 82 × 53⁄4 ft (1982); Stratford Park, Glos., 60 × 51⁄2 ft (1984); Eastnor Castle, Heref., 50 × 71⁄2 ft and 52 × 71⁄4 ft (1977); Whiteways, Devon, 79 × 61⁄2 ft (1978); Pencarrow, Cornwall, 66 × 4 ft (1978); Mount Usher, Co. Wicklow, Eire, 70 × 73⁄4 ft (1975).
The three related species mentioned on page 232 have all been given the rank of subspecies of A. saccharum by Y. Desmarais in Brittonia, Vol. 7, pp. 347–87 (1952), A. barbatum as A. s. subsp. floridanum. The key character he uses to separate A. nigrum (A. s. subsp. nigrum) is that its leaves are yellowish green beneath and usually pubescent with short erect hairs, against glaucous or whitish and usually glabrous beneath in typical A. saccharum. See also E. Murray in Kalmia, Vol.7, pp. 13–19 (1975).
The example of A. nigrum in the Edinburgh Botanic Garden measures 62 × 41⁄4 ft (1985).
This species was described by Bean (B231, S60) and Krüssmann (K104), and is an important maple in temperate tree collections and landscapes. Authorities recognise variable numbers of subspecific taxa. Desmarais (1952) constructed a key to six subspecies, though additional taxa are recognised by van Gelderen et al. (1994). Presented below is a key to seven subspecies (devised by Peter Gregory and used with his kind permission), with an indication of the distribution of each from van Gelderen et al. (1994). However, the delimitation of the various subspecies and varieties is complex, as morphological characters vary continuously across the vast range. Most of the A. saccharum subspecies are well known in cultivation, and were described by Bean (1976a) under different names (A. barbatum, A. grandidentatum, A. leucoderme, A. nigrum). Material from the southernmost population, recognised as subsp. skutchii, is new to cultivation and is described below.
Numerous cultivars of A. saccharum have been named, with varying characters useful for different sites and conditions. A summary guide is provided by Dirr (1998).
|1a.||Leaf underside pale green to glaucous||2|
|1b.||Leaf underside yellow-green, lobes shallow, central lobe with divergent margins||6|
|2a.||Leaves large (≥ 10–15 cm)||3|
|2b.||Leaves small (5–10 cm)||5|
|3a.||Leaves deeply lobed, margins of central lobe parallel to inwardly angled||4|
|3b.||Leaves shallowly lobed, margins of central lobe slightly divergent; USA (Illinois, Indiana, Missouri)||subsp. schneckii|
|4a.||Lobe tips acute, leaf undersides glabrous to pubescent with silky appressed hairs; widespread in eastern North America (Canada, Mexico, USA)||subsp. saccharum|
|4b.||Lobe tips bluntly pointed, leaf undersides pubescent and glaucous; Guatemala, Mexico (southern)||subsp. skutchii|
|5a.||Margins of central lobe parallel to slightly divergent, lobe tips bluntly pointed; Mexico, USA (Florida, Texas)||subsp. floridanum (Chapman) Desmarais|
|5b.||Margins of central lobe inwardly angled, lobe tips rounded; USA (Oklahoma and Texas to Arizona and Montana, especially Rocky Mts.)||subsp. grandidentatum|
|6a.||Leaves small (5–10 cm), undersides with soft appressed hairs, bark smooth, pale grey to chalky white; USA (Alabama, Arkansas, Florida, Georgia, Louisiana, N. Carolina, S. Carolina)||subsp. leucoderme (Small) Desmarais|
|6b.||Leaves large (≥ 10–15 cm), undersides with stiff, short, erect hairs, bark rough, dark grey-brown to black; Canada (Ontario, Quebec), USA (northeast, south to Kentucky, west to Michigan, Iowa, Kansas)||subsp. nigrum|
A. saccharum var. leucoderme (Small) Sarg
A. saccharum var. nigrum (Michx. f.) Britt
Subsp. skutchii forms a tree to 20 m tall. Branchlets glabrous. Leaves 12–16 × 14–20 cm, lower surface glaucous with dense tomentum on the veins. Samaras 2.5–4.5 cm long. Van Gelderen et al. 1994. Distribution GUATEMALA; MEXICO. Habitat Cloud forest over limestone. USDA Hardiness Zone 7–8. Conservation status Not evaluated. Illustration NT106.
This is the southernmost variant of the sugar maples, but its precise delimitation in the western Mexican mountains is not entirely clear (S. Hogan, pers. comm. 2007), as subspp. floridanum, grandidentatum and saccharum also penetrate Mexico (van Gelderen et al. 1994). Material from Tamaulipas in cultivation in the western United States appears to fit subsp. skutchii, and has large leathery leaves that persist into the New Year, when they colour red and fall slightly before or as the new leaves emerge, thus making the tree almost evergreen. At Tregrehan at least it has attractive pinkish spring growth (T. Hudson, pers. comm. 2007). There is a good specimen in the Hogan–Sanderson plantings in Northeast 11th Avenue, Portland, Oregon, and it is grown in the southeastern states from collections made by Yucca Do Nursery. It is rare in Europe, but a few examples are known. Tom Hudson (pers. comm. 2007) planted one in 1995 at Tregrehan but, in the belief that it was tender, put it in a sheltered site where competition from other trees has suppressed it, and it is still only 2 m in 2007. This taxon in fact appears to be extremely hardy, reported to tolerate at least –18 ºC, and to grow well in heavy clay soils (Raulston 1996), although leaves will be lost if temperatures fall below this (Hogan 2008).
A. rugelii Pax