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.