Betula papyrifera Marsh.

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).

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.