1	Female inflorescence narrowly cylindric; lateral lobes of bracts reduced; wings of nutlet partly exserted, much wider than nutlet; leaves irregularly and doubly setiform serrate.		(2)
+	Female inflorescence oblong-cylindric, oblong, or subglobose; lateral lobes of bracts distinct; wings of nutlet included; leaves irregularly or regularly doubly serrate.		(5)
2 (1)	Female inflorescences 2-5 in a raceme; bracts densely pubescent abaxially; leaves lanceolate or ovate-lanceolate, apex acuminate or caudate-acuminate		1 Betula alnoides
+	Female inflorescences 1 or 2.		(3)
3 (2)	Female inflorescence 1(or 2)		4 Betula luminifera
+	Female inflorescences 2.		(4)
4 (3)	Scales of buds glabrous; petiole glabrous except villous in furrow; bracts rhombic, 4-5 × ca. 3 mm, glabrous; nutlet 3-5 × 1.5-3 mm		2 Betula rhombibracteata
+	Scales of buds villous; petiole densely yellow villous; bracts oblong-lanceolate, 2-3 × 1.5-1.7 mm, pubescent at base; nutlet ca. 2 × 1-1.5 mm		3 Betula cylindrostachya
5 (1)	Nutlet narrowly bordered, not distinctly winged.		(6)
+	Nutlet with distinct, membranous wings.		(14)
6 (5)	Leaves leathery, midvein and lateral veins deeply impressed adaxially, distinctly raised abaxially.		(7)
+	Leaves papery, midvein and lateral veins sometimes slightly impressed adaxially, raised abaxially.		(10)
7 (6)	Trees to 12 m tall; bracts of male inflorescence yellow-brown tomentose		8 Betula jiulungensis
+	Shrubs or small trees to 5 m tall; bracts of male inflorescence yellow or white villous.		(8)
8 (7)	Leaves orbicular or broadly ovate, apex rounded or obtuse; petiole 1-2 mm; bracts of female inflorescence densely yellow villous		7 Betula calcicola
+	Leaves ovate-lanceolate or elliptic, apex acuminate or acute; petiole 3-5 mm; bracts of female inflorescence glabrous or pubescent.		(9)
9 (8)	Scales of buds glabrous; leaves densely yellow or white villous along veins except on reticulate veins abaxially, margin with 2 acute teeth between lateral veins		5 Betula potaninii
+	Scales of buds densely white tomentose; leaves densely yellow-brown tomentose along veins.abaxially, margin with 1(or 2) obtuse teeth between lateral veins		6 Betula trichogemma
10 (6)	Female inflorescences 4 in a raceme, cylindric; leaves 12-13 × 7-8 cm, densely yellow tomentose abaxially		9 Betula gynoterminalis
+	Female inflorescence 1, subglobose, ovoid, ovoid-oblong, or oblong-cylindric; leaves less than 10 × 5 cm, villous or glabrescent abaxially.		(11)
11 (10)	Trees to 35 m tall.		(12)
+	Shrubs usually to 5 m tall.		(13)
12 (11)	Trees to 35 m tall; bark black or black-brown; female inflorescence oblong-cylindric; peduncle 3-6 mm; bracts 4-5 mm, with lateral lobes ca. 1/2 as long as middle lobe		10 Betula schmidtii
+	Trees to 15 m tall; bark dark gray; female inflorescence ovoid or ovoid-oblong; peduncle 1-2 mm; bracts 5-10 mm, with lateral lobes subequal to middle lobe		11 Betula fargesii
13 (11)	Female inflorescence oblong-cylindric or oblong; lobes of bracts with apex not reflexed; leaves with 9-21 lateral veins on each side of midvein		12 Betula delavayi
+	Female inflorescence subglobose, rarely oblong; lobes of bracts with apex usually reflexed; leaves with 8 or 9 lateral veins on each side of midvein		13 Betula chinensis
14 (5)	Leaves with 8-15 lateral veins on each side of midvein.		(15)
+	Leaves with 3-8 lateral veins on each side of midvein.		(21)
15 (14)	Bud scales densely silky villous; leaves triangular-ovate, broadly ovate, or ovate; bark grayish white		20 Betula ermanii
+	Bud scales glabrous; leaves ovate, elliptic, oblong, or lanceolate; bark grayish black, dark brown, red-brown, or dark red-brown.		(16)
16 (15)	Wings of nutlet 1/4-1/2 as wide as nutlet; female inflorescence subsessile		14 Betula insignis
+	Wings of nutlet ca. 1/2 as wide as nutlet or more; female inflorescence pedunculate.		(17)
17 (16)	Wings of nutlet ca. 1/2 as wide as nutlet; female inflorescence 1-2.5 cm in diam.; peduncle only 2-3 mm or obscure; branchlets without resinous glands.		(18)
+	Wings of nutlet ca. as wide as nutlet; female inflorescence less than 1 cm in diam.; peduncle 8-15 mm; branchlets densely resinous glandular.		(19)
18 (17)	Female inflorescence 1, or 2 or 3 in a cluster, 4-5 × ca. 1 cm; bracts with a tuft of yellow hairs at base		15 Betula jinpingensis
+	Female inflorescence 1, 2.5-6 × 1.2-2.5 cm; bracts densely pubescent		16 Betula austrosinensis
19 (17)	Female inflorescence 1; bracts ciliate; bark grayish		19 Betula costata
+	Female inflorescence 1, or 2-4 in a raceme; bracts sparsely pubescent; bark red-brown or dark red-brown.		(20)
20 (19)	Leaves densely bearded in axils of lateral veins abaxially; bark dark red-brown		17 Betula utilis
+	Leaves usually not bearded in axils of lateral veins abaxially; bark orange-red or orange		18 Betula albosinensis
21 (14)	Trees.		(22)
+	Shrubs or dwarf shrubs.		(27)
22 (21)	Bark black-brown, fissured; wings of nutlet ca. 1/2 as wide as nutlet		26 Betula dahurica
+	Bark gray-white, yellow-white, light yellow-brown, or grayish brown, exfoliating; wings of nutlet ca. as wide as or wider than nutlet.		(23)
23 (22)	Leaves triangular, triangular-ovate, or triangular-rhombic, apex acuminate or caudate-acuminate.		(24)
+	Leaves ovate, rhombic, ovate-rhombic, or broadly ovate-rhombic, apex acute or acuminate.		(25)
24 (23)	Branches usually pendulous in mature trees; wings of nutlet ca. 2 × as wide as nutlet		22 Betula pendula
+	Branches not pendulous; wings of nutlet about as wide as nutlet		21 Betula platyphylla
25 (23)	Bark grayish brown; leaves ovate; wings of nutlet 1.5-2 × as wide as nutlet		23 Betula halophila
+	Bark grayish white, yellow-white, or yellow-brown; leaves rhombic, ovate-rhombic, or broadly ovate-rhombic; wings of nutlet ca. as wide as nutlet.		(26)
26 (25)	Bark grayish white; leaves rhombic or obovate-rhombic, base cuneate		24 Betula microphylla
+	Bark yellow-white or light yellow-brown; leaves broadly ovate-rhombic, base broadly cuneate		25 Betula tianschanica
27 (21)	Leaves suborbicular or broadly obovate.		(28)
+	Leaves ovate, broadly ovate, ovate-rhombic, elliptic-rhombic, obovate-elliptic, or broadly elliptic.		(29)
28 (27)	Leaves suborbicular; peduncle 3-4 mm; wings of nutlet ca. as wide as or slightly narrower than nutlet		31 Betula rotundifolia
+	Leaves broadly obovate; peduncle 8-10 mm; wings of nutlet slightly wider than nutlet		32 Betula middendorfii
29 (27)	Wings of nutlet 1-2 × as wide as nutlet		30 Betula gmelinii
+	Wings of nutlet ca. 1/2 as wide as nutlet.		(30)
30 (29)	Branchlets densely villous and pubescent; leaves obovate-elliptic, ovate-rhombic, elliptic-rhombic, or broadly elliptic, densely white villous on both surfaces when young; lateral lobes of bracts suberect or slightly spreading		27 Betula ovalifolia
+	Branchlets scabrous; leaves ovate, broadly ovate, or ovate-elliptic, glabrous; lateral lobes of bracts spreading or horizontal.		(31)
31 (30)	Bark grayish white; leaves densely glandular punctate on both surfaces, margin minutely serrate; peduncle (2-)3-10 mm		28 Betula fruticosa
+	Bark dark brown; leaves not glandular punctate, margin roughly serrate; peduncle 1-3 mm		29 Betula humilis