1. Leaves in cross section with 1 fibrovascular bundle; scales of fascicle sheaths shed early, not falling with fascicle, these and bud scales mostly with margins entire, less often finely ciliate or finely fringed; seed cones unarmed (except in P. balfouriana, P. aristata, P. longaeva)(subg. Strobus). | → 2 |
1. Leaves in cross section with 2 fibrovascular bundles; scales of fascicle sheaths, at least lower ones, persistent and falling with fascicle (except in P. leiophylla and P. torreyana), these and bud scales mostly with margins long-fringed; seed cones mostly armed (subg. Pinus). | → 14 |
2. Leaves mostly 5 per fascicle, 3-sided, straight or curved; open seed cones (cones of P. albicaulis do not open) narrowly ovoid to ± cylindric; seeds winged or wingless. | → 3 |
2. Leaves mostly 1-4 per fascicle, terete or 2-3-sided, stiff and strongly incurved; open seed cones depressed-ovoid to nearly globose; seeds wingless. | → 11 |
3. Fascicles persistent 10 or more years, forming a long brush; leaves curved, connivent, 5 cm or less; apophyses much thickened, umbos central; mature seed cones lanceoloid-cylindric before opening, purple to brown or red-brown, with prickles (prickles much reduced or absent in P. balfouriana), open cones lance-ovoid to ovoid or cylindric; seeds winged; alpine or timberline trees. | → 4 |
3. Fascicles persistent 8 or fewer years, not forming a long brush; leaves straight or curved, of various lengths; apophyses variously thickened, umbos terminal; mature seed cones variously shaped, pale brown to gray or gray-brown (purplish in P. albicaulis), without prickles; seeds winged or wingless; trees of various elevations. | → 6 |
4. Abaxial surface of leaves with strong, narrow median groove; prickle slender, long (mostly 6-10 mm). | P. aristata |
4. Abaxial surface of leaves lacking median groove or, if grooved, with grooves indistinct and more than 1; prickle to 6 mm or very reduced, weak, even absent. | → 5 |
5. Seed-cone base conic; apophysis rounded, umbo depressed, prickle absent or to 1 mm, weak; resin exudates on seed cone amber. | P. balfouriana |
5. Seed-cone base rounded; apophysis sharply keeled, umbo raised on low buttress, truncate or umbilicate, abruptly narrowed to slender prickle 1-6 mm; resin exudates on seed cone pale. | P. longaeva |
6. Seed wing at least as long as seed body; apophysis mostly not much thicker than subtending part of seed-cone scale; leaves straight, not persisting past 4-5 years; large trees of various elevations. | → 7 |
6. Seed wing lacking or shorter than seed body; apophysis mostly distinctly thicker than subtending portion of seed-cone scale; leaves straight or curved, persisting 5 years or more (except P. strobiformis); medium-sized to low trees mostly of high elevations. | → 9 |
7. Stomatal lines evident on all surfaces of leaves (best seen on younger growth); seed cones 25-50 cm; seed body 1-2 cm, wing 2-3 cm. | P. lambertiana |
7. Stomatal lines evident only on adaxial surface of leaves; seed cones 7-25 cm; seed body 0.5-0.7 cm, wing 1.8-2.5 cm. | → 8 |
8. Leaf apices broadly to narrowly acute; apophyses of mature scales creamy brown to yellowish, without purple or gray tints; bark of mature tree distinctly platy; w North America. | P. monticola |
8. Leaf apices abruptly acute to short-acuminate; apophysis of mature scales with purple or gray tints; bark of mature tree distinctly furrowed; e North America. | P. strobus |
9. Mature seed cones broadly ovoid to depressed-ovoid or nearly globose, 4-8 cm, remaining closed, scales readily broken off through animal agency. | P. albicaulis |
9. Mature seed cones lance-ovoid or lance-cylindric before opening, 7 cm or more, opening at maturity, scales firmly attached. | → 10 |
10. Apophyses of fertile scales recurved; bark of mature trunk thick, furrowed; stomatal lines not evident on abaxial leaf surface. | P. strobiformis |
10. Apophyses of fertile scales not recurved; bark of mature trunk thin, platy; stomatal lines evident on all leaf surfaces. | P. flexilis |
11. Leaves mostly 1 per fascicle, terete (sometimes with a strong groove on each side). | P. monophylla |
11. Leaves mostly 2-4(-5) per fascicle, mostly 2-3-sided. | → 12 |
12. Leaves 0.6-0.9(-1.0) mm wide, (2-)3(-4) per fascicle. | P. cembroides |
12. Leaves at least 1 mm wide, (1-)2-4 per fascicle. | → 13 |
13. Leaves (3-)4(-5) per fascicle; trees in s California and Baja California. | P. quadrifolia |
13. Leaves (1-)2(-3) per fascicle; trees in n Mexico and Rocky Mountains northward, rarely in California Sierra Nevada. | P. edulis |
14. Leaves 2(-3) per fascicle. | → 15 |
14. Leaves 3(-5) per fascicle. | → 28 |
15. Longer leaves of healthy branches 10-15 cm or more. | → 16 |
15. Longer leaves of healthy branches mostly 10-13 cm or less. | → 20 |
16. Seed cones mostly asymmetric, curved-ovoid when open, mostly in whorls, larger umbos forming claws; fascicle sheath mostly 1.5 cm or less; cones serotinous; California. | P. muricata |
16. Seed cones symmetric or nearly so, not curved when open, mostly not in whorls, umbos not forming claws; fascicle sheath mostly 1.5 cm or more; cones not serotinous; e North America or widespread in w North America. | → 17 |
17. Seed cones unarmed, mostly 6 cm or less; fresh leaves brittle, breaking cleanly when bent, ca. 1 mm wide or less; e boreal forest. | P. resinosa |
17. Seed cones armed, mostly 6 cm or more; fresh leaves pliant, not breaking cleanly when bent, mostly over 1 mm wide; se or w montane North America. | → 18 |
18. Seed cones stalked, chocolate brown, apophyses lustrous; se North America. | P. elliottii |
18. Seed cones sessile or nearly sessile, yellow-brown to brown or red-brown, apophyses rarely lustrous; se or w North America. | → 19 |
19. Healthy twigs to ca. 1 cm thick; terminal bud lance-cylindric, mostly less than 1 cm broad, slightly resinous; open seed cones narrowly ovoid, mostly dull yellow-brown; se North America. | P. taeda |
19. Healthy twigs 1-2 cm thick; terminal bud ovoid, fully 1 cm broad, very resinous; open seed cones broadly ovoid, mostly reddish brown; w North America. | P. ponderosa |
20. Seed cones evidently asymmetric, variably serotinous (except for P. contorta var. murrayana). | → 21 |
20. Seed cones symmetric or nearly so, not serotinous (except P. clausa). | → 24 |
21. Larger umbos extended into stout, curved claws; Appalachian Mountains and associated piedmont, not Alabama or Florida. | P. pungens |
21. Larger umbos not extended into claws; n, w North America, or Alabama and Florida. | → 22 |
22. Seed cones curved forward on branches, unarmed or with small reflexed apiculi. | P. banksiana |
22. Seed cones spreading to recurved on branches, mostly armed with prickles. | → 23 |
23. Twigs aging brownish, rough; w North America. | P. contorta |
23. Twigs aging gray, smooth or nearly so; Alabama and Florida. | P. clausa |
24. Leaves strongly twisted, longer ones mostly (2-)3-8 cm × 1 mm or broader; seed cones persistent or not. | → 25 |
24. Leaves straight, slightly twisted, fine, longer ones mostly 6-13 cm × ca. 1 mm; seed cones persistent. | → 26 |
25. Bark on upper sections of trunk orange, platy; leaves blue- to gray- or yellow-green, stomatal lines conspicuous; twigs at first dull green to orange-brown, not glaucous; seed cones unarmed, not persistent; adaxial surface of seed-cone scales lacking contrasting border distally; introduced Eurasian species. | sylvestris var. sylvestris |
25. Bark on upper sections of trunk reddish, scaly; leaves deep to pale yellow-green, stomatal lines inconspicuous; twigs at first red- or purple-tinged, often glaucous; seed cones armed, persistent; adaxial surface of seed-cone scales with strong purple-red or purple-brown border distally; native. | P. virginiana |
26. Twigs roughened and cracking below leafy portion; bark plates with evident resin pockets. | P. echinata |
26. Twigs smooth below leafy portion; bark plates lacking resin pockets. | → 27 |
27. Bark on upper sections of trunk reddish to red-brown, platy; seed cones often long-serotinous, long-persistent, usually armed with prickle; adaxial surface of seed-cone scales with dark red-brown, purple, or purple-gray border distally. | P. clausa |
27. Bark on upper sections of trunk gray, ± smooth, appearing slick; seed cones not serotinous, semipersistent, unarmed or with weak, short, deciduous prickle; adaxial surface of seed-cone scales lacking contrasting border distally. | P. glabra |
28. Pines of e North America (w to Missouri, e Oklahoma, and e Texas). | → 29 |
28. Pines of w North America (e to North Dakota, Nebraska, Colorado, and w Texas). | → 34 |
29. Longer leaves of healthy growth rarely more than 11 cm, mostly 5-11(-15) cm; seed cones 10 cm or less. | → 30 |
29. Longer leaves of healthy growth rarely less than 12 cm, mostly 15 cm or more; seed cones variable in length. | → 31 |
30. Two-year-old branchlets slender (ca. 5 mm thick or less); twigs at first greenish brown to red-brown, often glaucous; leaves ca. 1 mm wide, not or only slightly twisted; bark plates with evident resin pockets; adaxial surface of seed-cone scales lacking contrasting border distally. | P. echinata |
30. Two-year-old branchlets stout (mostly over 5 mm thick); twigs at first orange-brown; leaves 1-1.5(-2 mm) wide, twisted; bark plates without resin pockets; adaxial surface of seed-cone scales with dark red-brown border distally. | P. rigida |
31. Leaves 15-45 cm; pollen cones purplish. | → 32 |
31. Leaves mostly under 20 cm; pollen cones yellowish to brownish. | → 33 |
32. Terminal buds ovoid, silvery white, 3-4 cm; seed cones sessile (rarely short stalked), 15-25 cm, apophyses dull; leaves 20-45 cm. | P. palustris |
32. Terminal buds cylindric, silvery brown, 1.5-2 cm; seed cones stalked, (7-)9-18(-20) cm, apophyses lustrous (as if varnished); leaves 15-20(-23) cm. | P. elliottii |
33. Seed cones variably serotinous, long-persistent, broadly ovoid to nearly globose when open; umbos with short, weak prickle or none; adaxial surface of seed-cone scales with dark red-brown border distally; trunks commonly with adventitious shoots. | P. serotina |
33. Seed cones not serotinous, not persistent, narrowly ovoid when open; umbos with stout-based, sharp prickle; adaxial surface of seed-cone scales lacking dark border distally; trunks not producing adventitious shoots. | P. taeda |
34. Seed cones massive, heavy; apophyses much extended, particularly toward base of cone, continuous with umbo to produce a curved-tipped pyramid or long claw; seed body 1.5-2.5 cm; leaves 15-32 cm; California and Baja California. | → 35 |
34. Seed cones, if massive, not markedly heavy; apophyses, if extended, not continuous with umbo, umbo either unarmed or with prickle, outcurved claw, or apiculus; seed body to 1 cm; leaf length various; widespread. | → 37 |
35. Leaves mostly 5 per fascicle; larger apophyses and umbos forming short, curved-tipped pyramids; seed cones 10-15 cm. | P. torreyana |
35. Leaves mostly 3 per fascicle; larger apophyses and umbos curved, forming long claws; seed cones 15-35 cm. | → 36 |
36. Mature seed cones pale yellow-brown; leaves not drooping; larger claws (apophysis plus umbo) 2.5-3 cm; seed wing longer than seed body. | P. coulteri |
36. Mature seed cones dull brown; leaves drooping; larger claws (apophysis plus umbo) not over 2 cm; seed wing shorter than seed body. | P. sabiniana |
37. Fascicle sheath to 1.5 cm, completely shed; seed cones slender-stalked, 3.5-5(-9) cm, symmetric, umbo unarmed or producing a short, often deciduous prickle; leaves 6-15 cm × 0.8-1 mm; Arizona, New Mexico. | leiophylla var. chihuahuana |
37. Fascicle sheath mostly over 1.5 cm, its base persistent and falling with fascicle; seed cones sessile or nearly sessile, of various lengths, symmetry, and umbo form; leaves mostly over 1 mm wide and of various lengths; distribution various. | → 38 |
38. Seed cones strongly asymmetric, persistent, often serotinous; apophyses conspicuously extended, larger toward outside base of cone, there forming large angulate tubercles or mammillae; leaves mostly 9-15 cm. | → 39 |
38. Seed cones symmetric or slightly asymmetric, not persistent and not serotinous; apophyses mostly little extended; leaf length various. | → 40 |
39. Seed cones lanceoloid before opening; larger apophyses tubercular-angulate, umbos stout-triangular. | P. attenuata |
39. Seed cones ovoid before opening; larger apophyses less angular, more rounded, umbos mostly depressed. | P. radiata |
40. Leaves (20-)25-45 cm, often drooping; fascicle sheaths 3-4 cm; leaf margins harshly serrulate; closed seed cones sometimes curved; larger umbos producing outcurved claws. | P. engelmannii |
40. Leaves 7-25(-30) cm, not drooping; fascicle sheaths 1-2.5(-3) cm; leaf margins finely serrulate; closed seed cones not curved or only slightly so; umbos with prickle or claw not outcurved. | → 41 |
41. Lower scales of seed cones just prior to and after cone fall spreading and reflexed, thus well separated from adjacent scales; seed cones with steep spirals of 5-7 scales per row as viewed from side; buds very resinous; fresh-cut wood smelling of turpentine; umbo broadly pyramidal, narrowing to short, stout prickle or merely acute or depressed; widely distributed. | P. ponderosa |
41. Lower scales of seed cones just prior to and after cone fall not so spreading and reflexed, thus not well separated from adjacent scales; seed cones with low spirals of 8 or more scales per row as viewed from side; buds not resinous; fresh-cut wood with sweet or lemony fragrance; umbo pyramidal but narrowing abruptly at tip to slender, reflexed prickle; California, Nevada, Oregon. | → 42 |
42. Seed cones (10-)15-30 cm; abaxial surface of seed-cone scales neither darker than nor sharply contrasting in color with exposed adaxial surface; leaves 12-25 cm × ca. 1.5-2 mm. | P. jeffreyi |
42. Seed cones 7-10 cm; abaxial surface of seed-cone scales darker than and sharply contrasting in color with paler, adaxial surface; leaves 10-15 cm × ca. 1.5 mm. | P. washoensis |