Key to the Pines of the Southeastern United States
Source: Hardin, J. W. 1971. Studies of the southeastern United States flora. II. The gymnosperms. Journal of the Elisha Mitchell Scientific Society 87(2):43–50.
1.
Needles 5 per fascicle, sheath deciduous.
P. strobus
1.
Needles 2-4 per fascicle, sheath persistent; cone scales distally thick and often armed with a prickly umbo.
2.
2.
Annual growth uninodal, with 1 whorl; seed cones subterminal at end of shoot; cone scales unarmed.
P. resinosa
2.
Annual growth usually multinodal; seed cones lateral; cone scales usually armed with a prickly umbo.
3.
3.
Sheath longer than 13 mm; needles 3 per fascicle, 20-50 cm long; foliar buds 15-30 mm long with white fimbriate scales; seed cones (12)16-28 cm long.
P. palustris
3.
Sheath shorter than 15 mm; needles 2-4 per fascicle, 5-25 cm long; foliar buds less than 20 mm long, brownish or gray; cones less than 16 cm long.
4.
4.
Needles 3, very rarely 2 or 4, per fascicle.
5.
4.
Needles 2, or 2 and 3, per fascicle.
7.
5.
Older twigs brown; needles flexible; foliar buds not resinous; seed cone 7 cm or longer, sessile and seldom reflexed, umbos with a stout prickle; seeds usually more than 2 mm thick.
P. taeda
5.
Older twigs orange-brown; needles stiff; foliar buds resinous; seed cone less than 7 cm long, pedunculate and usually reflexed, umbos with small prickle or flat; seeds seldom more than 2 mm thick.
6.
6.
Needles 15 cm or longer; seed cones serotinous, broad-ovoid to globose, usually more than 3.7 cm wide, with a small prickle.
P. serotina
6.
Needles less than 15 cm long; seed cones opening, narrowly to broadly ovoid, usually less than 3.7 cm wide, umbo slightly raised and with a small usually persistent prickle.
P. rigida
7.
Needles over 13 cm long; seed cones 6-16 cm long, not persisting.
8.
7.
Needles less than 13 cm long; seed cones less than 10 cm long, persisting for several years.
9.
8.
Seedlings with erect, slender, pencil-like stems and scattered buds; needles in fascicles of 2-3 on the same tree; opened seed cones usually flattened at base.
P. elliottii var.
elliottii
8.
Seedlings with grass stage; needles mainly 2, infrequently 3 per fascicle; opened seed cones usually rounded at base.
P. elliottii var.
densa
9.
Seed cones light brown and lustrous, scales armed with a very broad, stout, upwardly-curved prickle.
P. pungens
9.
Seed cones dull brown or gray, scales armed with a slender, weak or stout prickle.
10.
10.
Bark on small branches loose, blackish, flaking off and showing orange-tinged inner bark; few 3-needle fascicles.
P. echinata
10.
Bark on small branches smooth, gray; only 2-needle fascicles present.
11.
11.
Needles to 8 cm long; cones about 5 cm long, with weak or deciduous prickles.
P. glabra
11.
Needles 8 cm or less; cones about 8 cm long, wih persistent slender prickles.
12.
12.
Needles twisted, cones opening at maturity, seed wings about 7 × 3 mm.
P. virginiana
12.
Needles not twisted, cone opening or serotinous, seed wings to 20 × 6 mm.
P. clausa