1	Needles with basal sheath deciduous and basal scalelike leaves not decurrent, cross section with 1 vascular bundle; umbo terminal or dorsal.		(2)
+	Needles with basal sheath persistent and basal scalelike leaves decurrent, cross section with 2 vascular bundles; umbo dorsal.		(16)
2 (1)	Umbo dorsal; needles 3-5 per bundle.		(3)
+	Umbo terminal; needles (2-)5 per bundle.		(5)
3 (2)	Needles 4 or 5 per bundle; bark dark brown, flaking		25 Pinus squamata
+	Needles 3 per bundle; bark white, irregularly flaking.		(4)
4 (3)	Seed cones 12-20 cm; seeds cylindric, ca. 2.5 cm		26 Pinus gerardiana
+	Seed cones 5-7 cm; seeds ovoid, ca. 1 cm		27 Pinus bungeana
5 (2)	Seeds wingless or only shortly winged.		(6)
+	Seeds long winged.		(10)
6 (5)	Seed cones dehiscent at maturity; branchlets glabrous.		(7)
+	Seed cones indehiscent or imperfectly dehiscent; branchlets densely pubescent.		(8)
7 (6)	Seeds wingless or ridged along abaxial margin; seed coat thick; apophyses not or slightly reflexed.at margin		31 Pinus armandi
+	Seeds with a rudimentary wing 2-7 mm; seed coat thin; apophyses obviously reflexed at margin		32 Pinus fenzeliana
8 (6)	Needles slender, 4-8 cm × 0.5-1 mm; resin canals 2, marginal; shrubs		28 Pinus pumila
+	Needles stout, 7-12 cm × 1-1.5 mm; resin canals 3, median; trees.		(9)
9 (8)	First-year branchlets with red-brown hairs; needles with 6-8 blue-gray stomatal lines along each abaxial surface; seed cones 9-14 cm; seed scales acuminate at apex, recurved		29 Pinus koraiensis
+	First-year branchlets with yellow-brown hairs; needles with 3-5 gray-white stomatal lines along each abaxial surface; seed cones 5-8 cm; seed scales rounded at apex, incurved		30 Pinus sibirica
10 (5)	Needles 7-20 cm; seed cones cylindric to narrowly cylindric, 7-25 cm.		(11)
+	Needles less than 8 cm; seed cones ovoid, ovoid-ellipsoid, or ellipsoid-cylindric, usually less than 10 cm.		(13)
11 (10)	Needles not pendulous, 6-14 cm; seed cones 7-20 cm		38 Pinus strobus
+	Needles pendulous, (6-)11-24 cm; seed cones 10-30 cm.		(12)
12 (11)	Needles dark green adaxially; 1st-year branchlets green with faint bloom, glabrous; abaxial resin canal of needles always median		34 Pinus wallichiana
+	Needles grass green adaxially, conspicuously whitish bloomed on 2 abaxial surfaces; 1st-year branchlets conspicuously whitish bloomed, glandular pubescent; 1(or 2) abaxial resin canal(s) of needles always asymmetrically placed		33 Pinus bhutanica
13 (10)	Needles less than 1 mm in diam.; seed cones sessile or shortly pedunculate.		(14)
+	Needles 1-1.5 mm in diam.; seed cones distinctly pedunculate.		(15)
14 (13)	Branchlets densely pubescent; seed cones sessile; seeds as long as broad wing; needles 3.5-5.5 cm		39 Pinus parviflora
+	Branchlets glabrous or puberulent; seed cones shortly pedunculate; seeds ca. 1/2 as long as narrow wing; needles 4-8 cm		35 Pinus morrisonicola
15 (13)	Branchlets densely pubescent; resin canals 3, median		36 Pinus wangii
+	Branchlets glabrous, rarely puberulent; resin canals 2, marginal, sometimes also 1 median		37 Pinus kwangtungensis
16 (1)	Wing adnate to seed; needles 3 per bundle; apophyses distinctly protruded, with transverse ridges and spiny umbo		1 Pinus roxburghii
+	Wing articulated to seed; needles 2-5 per bundle; apophyses and umbo of different types.		(17)
17 (16)	Needles (2 or)3(-5) per bundle.		(18)
+	Needles 2(or 3) per bundle.		(28)
18 (17)	Trunk and branches usually with adventitious sprouts; needles mostly to 20 cm.		(19)
+	Trunk and branches usually without adventitious sprouts; needles mostly 15-45 cm.		(21)
19 (18)	Needles 2(or 3) per bundle, ca. 1 mm in diam.; winter buds 0.5-0.7(-1) cm in diam.; bark plates with evident resin pockets; adaxial surface of seed scales lacking contrasting border distally		11 Pinus echinata
+	Needles 3(-5) per bundle, 1-1.5(-2) mm in diam.; winter buds 1-1.5(-2) cm in diam.; bark plates without evident resin pockets; adaxial surface of seed scales with dark red-brown border distally.		(20)
20 (19)	Needles (12-)15-21 cm, slightly twisted; branchlets initially orange or yellow-orange, often glaucous; seed cones late dehiscent after maturity		12 Pinus serotina
+	Needles 5-10(-15) cm, twisted; branchlets initially orange-brown, not glaucous; seed cones dehiscent at maturity		13 Pinus rigida
21 (18)	Needles slender, 10-30 cm × 0.7-1.2 mm (except P. yunnanensis var. pygmaea with stout needles 5-13 cm).		(22)
+	Needles ± stout, 12-45 cm × 1.5-2 mm.		(24)
22 (21)	Umbo blunt or shortly mucronate in apical part of cone; needles 2(or 3) per bundle, 12-20 cm, slightly twisted		2 Pinus massoniana
+	Umbo shortly mucronate; needles (2 or)3 per bundle, 10-30 cm, not twisted.		(23)
23 (22)	Needles slender and pliant, less than 1 mm in diam.; resin canals marginal; apophyses ± pyramidal, distinctly cross keeled		3 Pinus kesiya
+	Needles relatively stout and stiff (slender and pliant in plants growing in dry, hot valleys), 1-1.2 mm in diam.; resin canals marginal and median; apophyses swollen, usually not pyramidal, not or slightly cross keeled		4 Pinus yunnanensis
24 (21)	Winter buds 3-4 cm, silvery white; seed cones 15-25 cm		14 Pinus palustris
+	Winter buds to 2 cm, reddish, chestnut, orange, or silvery brown; seed cones usually 5-15 cm.		(25)
25 (24)	Seed cones pedunculate.		(26)
+	Seed cones sessile or subsessile.		(27)
26 (25)	Seed cones (7-)9-18(-20) cm, all deciduous; umbo central, depressed-pyramidal, with a stout, short prickle; needles 2 or 3 per bundle		15 Pinus elliottii
+	Seed cones 5-10(-12) cm, often a few basal cones persistent; umbo slightly projecting, ending in a straight, minute prickle; needles (2 or)3(-5) per bundle		16 Pinus caribaea
27 (25)	Branchlets ca. 1 cm in diam.; terminal bud lanceolate-cylindric, mostly less than 1 cm wide, slightly resinous; seed cones mostly dull yellow-brown, narrowly ovoid when open		17 Pinus taeda
+	Branchlets 1-2 cm in diam.; terminal bud ovoid, ca. 1 cm wide, very resinous; seed cones mostly reddish brown, broadly ovoid when open		18 Pinus ponderosa
28 (17)	Needles mostly 20-30 cm or more.		(29)
+	Needles mostly less than 20 cm.		(33)
29 (28)	Umbo blunt or with sunken, short mucro.		(30)
+	Umbo ± spiny or pointed at apex.		(31)
30 (29)	Needle with 2 resin canals; seed cones red-brown at maturity		6 Pinus latteri
+	Needle with up to 9 resin canals; seed cones pale brown at maturity		19 Pinus tropicalis
31 (29)	Seed cones borne on stalks to 3 cm, chocolate brown; apophyses lustrous		15 Pinus elliottii
+	Seed cones sessile or subsessile, brown, yellow-, or red-brown; apophyses rarely lustrous.		(32)
32 (31)	Branchlets ca. 1 cm in diam.; terminal bud lanceolate-cylindric, usually less than 1 cm wide, slightly resinous; seed cones usually dull yellow-brown, narrowly ovoid when open		17 Pinus taeda
+	Branchlets 1-2 cm in diam.; terminal bud ovoid, ca. 1 cm wide, very resinous; seed cones usually reddish brown, broadly ovoid when open		18 Pinus ponderosa
33 (28)	Seed cones 9-18 cm		20 Pinus pinaster
+	Seed cones usually not more than 8 cm.		(34)
34 (33)	Needles slender and pliant, ca. 1 mm in diam.; apophyses relatively thin, flat or slightly raised.		(35)
+	Needles stout, 1-2 mm in diam.; apophyses ± swollen or pyramidal.		(37)
35 (34)	Trunk and branches usually with adventitious sprouts; umbo with a stout, sharp prickle		11 Pinus echinata
+	Trunk and branches usually without adventitious sprouts; umbo flat or blunt.		(36)
36 (35)	Needles 12-20 cm, slightly twisted		2 Pinus massoniana
+	Needles 5-12 cm, straight 7. P. densiflora		(34)
37 (34)	Needles shorter, longest ones not more than 8 cm, strongly twisted.		(38)
+	Needles (5-)9-16 cm, straight or rarely slightly twisted.		(40)
38 (37)	Seed cones strongly asymmetric, curved forward on branches; needles 2-5 cm		23 Pinus banksiana
+	Seed cones symmetric or nearly so; needles usually longer.		(39)
39 (38)	Bark on distal sections of trunk orange, plated; needles blue-, gray-, or yellow-green, stomatal lines conspicuous; branchlets initially dull green or orange-brown, not glaucous; adaxial surface of seed scales lacking contrasting border distally		10 Pinus sylvestris
+	Bark on distal sections of trunk reddish, scaly; needles deep to pale yellow-green, stomatal lines inconspicuous; branchlets initially red or purple tinged, often glaucous; adaxial surface of seed scales with strong purple-red or -brown border distally		24 Pinus virginiana
40 (37)	Seed cones deciduous.		(41)
+	Seed cones persistent.		(42)
41 (40)	Winter buds silvery white, cylindric-ellipsoid or cylindric		21 Pinus thunbergii
+	Winter buds brown, ovoid or oblong-ovoid		22 Pinus nigra
42 (40)	Needle with resin canals median, rarely also marginal; needles 4.5-17 cm; seed cones 3-6 cm		8 Pinus taiwanensis
+	Needle with resin canals marginal, occasionally 1 or 2 median; needles 6-15 cm; seed cones 2.5-9 cm.		(43)
43 (42)	Bark initially reddish brown, becoming dark grayish brown; 1st-year branchlets shiny yellowish brown; needle sheaths initially 0.5-1 cm; resin canals 3 or 4; pollen cones 1-1.8 cm; seed cones shiny chocolate brown at maturity		5 Pinus densata
+	Bark dull grayish brown or dark gray; 1st-year branchlets light grayish brown, light brown, or yellowish brown; needle sheaths initially 1-2 cm; resin canals 5-9; pollen cones 0.5-0.9 cm; seed cones yellowish brown to brown at maturity		9 Pinus tabuliformis