[Betula alba var. commutata Regel, moreBetula kenaica W.H.Evans, Betula neoalaskana var. kenaica (W.H.Evans) B.Boivin, Betula papyrifera var. commutata (Regel) Fernald, Betula papyrifera var. elobata (Fernald) Sarg., Betula papyrifera var. kenaica (W.H.Evans) A.Henry, Betula papyrifera var. macrostachya Fernald, Betula papyrifera var. pensilis Fernald, Betula papyrifera var. subcordata (Rydb. ex B.T.Butler) Sarg.]
Trees , to 12 m; crowns narrow. Bark dark reddish brown, sometimes becoming pinkish or grayish white, smooth, in maturity exfoliating in thin sheets; lenticels dark, horizontally expanded. Twigs without taste and odor of wintergreen, slightly to moderately pubescent, often with scattered resinous glands. Leaf blade ovate to nearly deltate with 2--6 pairs of lateral veins, 4--5(--7.5) × 2.5--4.5 cm, base rounded to cuneate, margins coarsely doubly serrate to dentate, teeth relatively sharp, apex acute to short-acuminate; surfaces abaxially sparsely to moderately pubescent, especially along major veins and in vein axils, often with scattered resinous glands. Infructescences erect to nearly pendulous, cylindric, 2--5 × 0.5--1 cm, shattering with fruits in fall; scales ciliate, lobes diverging at middle, nearly equal in length, strongly divergent. Samaras with wings as broad as to somewhat narrower than body, broadest near middle, not extended beyond body apically. 2 n = 70. Flowering late spring. Rocky slopes in the subalpine zone; 0--300 m; Yukon; Alaska. The relationship of Betula kenaica to other white-barked birches is not well understood, although it and the following species are evidently closely allied to B . papyrifera , from which they have likely been derived. Betula kenaica differs from B . papyrifera primarily in its smaller stature and in its smaller, blunter-tipped, more coarsely and regularly serrate leaves. Betula × hornei Butler (= Betula kenaica W. H. Evans × B . nana Linnaeus), variously intermediate between its parents, is common throughout the range of B . kenaica (which is mostly overlapped by that of B . nana ).
Tree 15 - 22 m tall, trunk 30 cm - 0.6 m in diameter Leaves: alternate, solitary on long shoots, in groups of three on spur shoots, stalked, dark green above, lighter beneath, 5 - 8 cm long, 3 - 5 cm wide, egg-shaped to nearly triangular, coarsely toothed except near base, early leaves becoming smooth, late leaves retaining hairs (sometimes only in leaf axils), with three to nine pairs of veins. Fall color is brilliant yellow. Flowers: either male or female, found on the same tree (monoecious), borne in catkins. Male catkins are brown, 7 - 10 cm long, and hang in pairs or small clusters. Female catkins green, 3 - 4 cm long, erect. Fruit: a seed with wide wings on each side (samara), borne in stalked, drooping catkins 3 - 4 cm long, scales shaped like a cross and hairy along the margin, catkins falling apart when ripe. Bark: dark reddish brown when young, changing to creamy white with long corky horizontal lines (lenticels) on trunk and large branches, exfoliating in thin paper-like sheets to reveal orange inner bark, becoming furrowed and dark at the base. Twigs: slender, changing from dull red to shiny orangish brown. Short spur shoots develop on older growth. Terminal buds: absent. Form: changing from loosely pyramidal to irregularly rounded or oval, single- or multi-trunked. End and lateral buds: 5 - 7 mm long, narrow egg-shaped with a short-pointed tip, slightly flattened, scales green on lower half and changing to brown and hairy near margin.
Similar species: Three white-barked birches grow in the Chicago Region: Betula papyrifera, Betula pendula, and Betula populifolia. Betula populifolia has bark that does not exfoliate and develops black triangles below the branches, leaves that are widest at the base with a long-pointed tip, and male catkins that are usually borne singly. Betula pendula has bark that rarely exfoliates but develops diamond-shaped black fissures, especially near the base, leaves that are widest at the base with a long pointed tip, and male catkins that are usually borne in pairs.
Flowering: mid April to mid May
Habitat and ecology: Most Chicago Region specimens are found in the counties surrounding Lake Michigan, because the climate and soil combination found there is desireable for this species. It grows on clay ravine slopes on Lake Michigan bluffs, cool wooded ravines, and wooded swamps. Betula papyrifera germinates better after a fire as the seeds are exposed to mineral soil. Fire also stimulates multiple sprouts from damaged trees.
Occurence in the Chicago region: native
Notes: The wood is used for pulpwood, veneer, burning in fireplaces, bobbins, handles, spools, and dowels. Native Americans used to make canoes, wigwam coverings and utensils with the bark. This species makes a better landscape tree than B. pendula in the Chicago Region.
Etymology: Betula is the Latin name for birch. Papyrifera comes from the Latin words for paper-bearing, referring to the bark.
Usually a small to middle-sized tree, occasionally to 30 m, often slightly leaning rather than strictly erect; bark white or nearly so, with horizontal (often semilunate) black marks about the branches, easily separable into thin layers, the peeled plates showing salmon-pink on the inside; lvs ovate, 5-10 cm, acuminate, sharply serrate or doubly serrate, cuneate to rounded at base, glabrous above, very sparsely pubescent beneath, usually only along the veins or in the vein-axils; fruiting catkins 3-5 cm; scales 3.9-6.2 mm, two-thirds to fully as wide, the lateral lobes broadly falcate-obovate, divergent, the middle lobe tapering; frs oblate, deeply retuse, broadly winged, 1.8-3.4 n2.7-5 mm, the body 0.9-1.5 mm wide; mostly polyploid, often 2n=70. Seral in moist or dry soil after fire or other disturbance; Lab. to Alas., s. to N.J., W.Va., n. Ind., and ne. Io. Becoming very dwarf at and above timberline in the White Mts. of N.H. and perhaps elsewhere. Most of our plants are var. papyrifera, as described above. The well marked but wholly confluent var. cordifolia is separately described.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.