A tree 60 to 70 ft high, with a rather thin, open head of branches, sometimes pendulous at the ends. Bark of the trunk one of the whitest among birches, mostly very smooth, but coming away in thin, paper-like layers; young shoots warty, the hairs with which they are furnished when quite young soon falling away. Leaves ovate, rounded, sometimes heart-shaped at the base, slender-pointed; 11⁄2 to 31⁄2 in. long, two-thirds as wide; margins irregularly, often doubly toothed, and hairy; upper surface dull dark green, with scattered hairs; lower surface pale, downy in the axils of the veins, dotted with small black glands; veins in six to ten pairs; stalks up to 1 in. long. Male catkins up to 4 in. long. Fruiting catkins drooping, about 11⁄2 in. long, 1⁄4 to 1⁄3 in. thick; scales usually glabrous, the lateral lobes broader than the middle one.
Native of N. America, where it stretches right across the upper latitudes as far north as Labrador and Hudson's Bay, and south to Iowa and Nebraska; introduced in 1750. It is the most widely spread of all American birches, and the most useful tree of the inclement far north, providing the dwellers in those regions with fuel. The bark was used for roofing, to make drinking utensils, and especially canoes. In gardens it is valuable for the effect the vivid white trunk produces. In this respect it is not more attractive than our native white birch, nor has it the same delicate grace, its leaves being larger and less numerous; but the trunk remains white to a greater size. It varies very much, as might be expected from its wide distribution some trees have drooping branches, others erect.
The following are the largest paper birches recorded in recent years: Lydhurst, Sussex, 73 × 41⁄4 ft (1965); Woburn, Beds., 69 × 41⁄4 ft (1958); Tortworth, Glos., 69 × 51⁄4 ft, and two others of about the same size (1964); Hergest Croft, Heref., 60 × 41⁄2 ft (1961).
var. commutata (Reg.) Fern. B. lyalliana Bean; B. alba subsp, occidentalis var. commutata Reg., B. occidentalis Sarg., not Hook.; B. papyrifera var. occidentalis Sarg. – There has been a good deal of confusion about this tree. The first synonym is the name under which it appeared in earlier editions of this work; the last is the one under which it will be found in the second edition of Sargent's Manual of the Trees of N. America. Sargent thought that this tree was B. occidentalis Hook., but Hooker's description clearly applies to the plants which Sargent named B. fontinalis, and it is for these that the name B. occidentalis must be used.
This variety is one of the very finest of birches, and reaches sometimes 120 ft in height; bark reddish brown to whitish, peeling. Young shoots warted, downy, yellowish brown. Leaves ovate with a rounded or heart-shaped base, ordinarily 3 to 4 in. long, but on young trees often over 5 in. long; hairy along the midrib and veins beneath; veins in seven to ten pairs. A native of British Columbia and Washington, inhabiting moist situations. There are two specimens of this birch in the Victory Glade at 'Westonbirt, the taller 58 × 31⁄2 ft (1966); they were catalogued as B. lyalliana.
var. cordifolia (Reg.) Fern. B. cordifolia Reg. – A small tree or shrub found in Labrador, Newfoundland, and in the mountains of the E. United States. Leaves double-toothed, heart-shaped or truncate at the base. It is thought by some authorities to be a fertile hybrid between B. papyrifera and B. lutea.
var. humilis (Reg.) Fern. & Raup B. alba subsp. papyrifera var. humilis Reg.; B. neoalaskana Sarg.; B. papyrifera var. neoalaskana (Sarg.) Raup – A tree 40 to 60 ft high, with the young shoots thickly covered with viscid warts, not downy. Leaves triangular-ovate, wedge-shaped or cut straight across at the base (heart-shaped on strong shoots), taper-pointed, 11⁄2 to 3 in. long, 1 to 2 in. wide; coarsely and often doubly toothed; glossy dark green, viscid, and slightly hairy; stalks 1⁄2 to 1 in. long, reddish. Fruiting catkins 1 to 11⁄4 in. long; scales hairy on the margin only, the side lobes larger, rounder, and broader than the middle one.
Native of Alaska, especially in the Yukon Valley; introduced in 1905. A tree sent to Kew by Prof. Sargent is thriving very well. It is in some respects like B. occidentalis, but differs in its thin, peeling, reddish-brown or dull white bark, and in the broader wing to the seeds. Sargent describes it as the common birch of the Yukon Valley. There is a slender, fast-growing specimen in the Edinburgh Botanic Garden, pl. 1951 and measuring 42 × 11⁄2 ft (1968).
var. kenaica (Evans) Henry B. kenaica Evans – Leaves 11⁄2 to 2 in. long, ovate; irregularly, coarsely, often doubly toothed, tapered at the base; at first minutely downy above, becoming glabrous; veins in five or six pairs; stalk slender, 3⁄4 to 1 in. long. The bark of the trunk is creamy white to reddish brown, and separates into layers. The tree grows 30 or 40 ft high, and is a native of the coast of Alaska. Introduced to Kew in 1891. It differs from the type in the fruit-scales being hairy on the margin, and in the smaller leaves.
var. subcordata (Rydb.) Sarg. B. subcordata Rydb. – A small tree with a silvery-grey or purplish-brown bark, found in British Columbia and adjoining parts of the United States, and thence eastward to Alberta, Montana, and Idaho. Leaves irregularly toothed or double-toothed, rounded to subcordate at the base, glabrous. Scales of fruiting catkins downy and ciliate.
From the Supplement (Vol. V)
specimens: Greenwich Park, London, 70 × 53⁄4 ft (1984); R.H.S. Garden, Wisley, Surrey, 58 × 33⁄4 ft (1980); Hall Place, Kent, 75 × 51⁄2 ft (1984); Lydhurst, Sussex, 74 × 41⁄2 ft (1980); Borde Hill, Sussex, 56 × 6 ft (1976); Crowsley Park, Oxon., 65 × 6 ft, a fine tree (1978); University Parks, Oxon., 58 × 51⁄4 ft (1981); Ascott, Bucks., 52 × 61⁄4 ft (1978); Colesbourne, Glos., 85 × 51⁄4 ft (1984); Westonbirt, Glos., the tree in Victory Glade measured in 1966 is not this species; Hergest Croft, Heref., 80 × 51⁄2 ft (1985); Sidbury Manor, Devon, 66 × 63⁄4 ft (1977); Cockington Court, Devon, 62 × 61⁄2 ft (1984); University Botanic Garden, Cambridge, 66 × 61⁄2 ft, an old tree mentioned by Elwes and Henry early this century, now almost static (1984); Edinburgh Botanic Garden, 66 × 6 ft (1981), 70 × 5 ft and 60 × 51⁄2 ft (1985); Benmore, Argyll, 72 × 83⁄4 ft (1983); Innes House, Moray, 50 × 81⁄4 ft (1980); Belvoir Park, Co. Down, 70 × 71⁄4 ft (1976); National Botanic Garden, Glasnevin, Eire, 52 × 51⁄4 ft (1980).
var. commutata – Regel based this variety on two Lyall specimens from western North America and one from Massachusetts, distinguishing it from typical B. papyrifera only by the shape of the bract-scales of the fruiting catkins. Some later botanists have treated it as more or less coincident with the later-named var. lyalliana, as the race of paper birch found in southern British Columbia and bordering Washington, west of the Cascades, said to be characterised by its greater size, reddish brown bark and larger, thinner leaves. But recent researchers have questioned whether this variety is really worth recognising, since paper birches with a dark, not peeling, bark occur throughout the range of the species. It has been pointed out that a tree in the Arnold Arboretum, raised from seeds received from Kaslo, British Columbia, in 1906, has a white bark, although the parent trees would certainly have been brown-barked. This suggests that the colour of the bark, and the readiness with whch it peels, may be determined by environmental factors (Fernald, Rhodora, Vol. 47, p. 312; Brittain and Grant, Canad. Field-Nat., Vol. 80, pp. 147-57; Janet Dugle, Canad. Journ. Bot., Vol. 44, p. 949 (1966)). As for the larger and thinner leaves of var. commutata, it was long ago suggested that this character is induced by the favourable soil and climate.
var. cordifolia – By some authorities this is treated as an independent species – B. cordifolia Reg. It differs from B. papyrifera in having leaves usually cordate at the base, with more numerous teeth on each side, longer female catkins, of which the bracts are longer, with differently shaped lateral lobes (Brittain and Grant, Canad. Field-Nat., Vol. 81, pp. 116-217 (1967)). It has also been suggested that it is the result of hybridisation between the paper birch and the yellow birch (B. alleghaniensis). It is a native mainly of north-eastern North America, from Labrador to New England, west to the region of the Great Lakes, but also occurs in the mountains as far south as North Carolina.
var. humilis – It is now widely agreed that B. neolaskana, placed under this by Fernald and Raup, should revert to the rank of species. See B. neoalaskana in this supplement.
var. kenaica – It should have been added that the bark of this birch becomes rough and fissured on old trees. It was originally described, as a species, in 1899, from specimens collected on the Kenai peninsula of Alaska, near the site of what is now Anchorage airport.
The taxonomic position of this birch is controversial. It was placed under B. papyrifera as a variety by Augustine Henry, followed by many American authors. But the Swedish botanists Lindquist and Jansson have both seen it as a member of the group of east Asiatic white birches, linked to those of Japan, China and the Russian Far East by the white birch of the Kamchatka peninsula (see in this supplement under B. mandshurica). Indeed, the former went so far as to place these birches under B. kenaica as varieties, while Jansson united the Kenai birch with the Kamchatka birch, making the illegitimate combination B. kamtschatica (Reg.) Jansson var. kenaica (Evans) Jansson.
var. subcordata – This variety is probably the result of hybridisation between B. papyrifera and B. occidentalis (fontinalis). Its leading characters are the smaller, acute (scarcely acuminate) leaves and the glandular twigs (Hitchcock, Vasc. Pl. Pacif. Northwest, Part 2, pp. 81-2). It was originally described from western Idaho, which is probably the eastern limit of its range.