
Vascular Flora of the Southeastern United States
Hardin, Massey, Radford, Thieret, eds.
Copyright - James W. Hardin, Ph. D., 1998, 1999. All Rights Reserved.
1.PINUS L. PINE
Evergreen trees initially conical, often becoming irregularly branched with a long, clear trunk and rounded or variously shaped crown. Leaves of two types. The primary leaves spirally arranged and reduced to small scales. Secondary leaves acicular (needle-like), borne in clusters of 2-5(6) on determinate short-shoots (forming a fascicle), and surrounded at the base by a persistent or caducous sheath of modified bud scales, the entire fascicle in the axil of a primary leaf and deciduous after 2 or more years. Pollen cones axillary, elongate-cylindrical. Ovulate or seed cones subterminal or lateral, relatively small the first spring (at pollination) and enlarging slightly before the second spring (at fertilization), then enlarging greatly to the mature size by that fall. Seed cones serotinous (remaining closed long after seeds are mature) or opening immediately at maturity , often persisting on the tree after seed drop; scales longer than the bracts, thickened or thin apically and the exposed part (apophysis) usually rhombic in outline, and often with a prominent terminal or lateral umbo terminated by a prickle, persisting on the cone axis.
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1. Needles 5(6) per fascicle, sheath caducous; seed cones narrowly cylindrical,
scales thin apically; primary leaf not decurrent, caducous (subgenus Strobus)
.....1. P. strobus.
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1. Needles 2-4 per fascicle, sheath persistent; seed cones broadly cylindrical,
ovoid, or globose, scales thick apically; primary leaves decurrent and
persistent (subgenus Pinus).
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2. Needles in fascicles of 3, very rarely 2 or 4, or 2 and 3 in P. elliottii
and P. echinata.
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3. Seed cones 7 cm or less long, pedunculed.
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4. Needles flexible, 15 cm or more long; seed cones broadly ovoid to globose,
usually more than 3.7 cm in diam., umbo flat and with a small prickle .....2.
P. serotina.
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4. Needles stiff, 15 cm or less long; seed cones narrowly to broadly ovoid,
usually less than 3.7 cm in diam., umbo slightly raised and with a small,
usually persistent, curved prickle .....3.
P. rigida.
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3. Seed cones 7 cm or more long, sessile or nearly so.
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5. Needles 14-26 cm long; bud scales brown-red and smooth-margined; seed
cones 7-13 cm long .....4. P. taeda.
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5. Needles 25-50 cm long; bud scales silvery-white and fimbriate; seed
cones 12-28 cm long .....5. P. palustris.
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2. Needles in fascicles of 2, rarely 3 in P. pungens and 2 and 3 in P.
elliottti and P. echinata.
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6. Needles 11 cm or more long; fascicle sheath 7 mm or more long.
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7. Seed cones 4-8 cm long, scales without a prickle or the minute prickle
soon dropping .....6. P. resinosa.
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7. Seed cones 9-15 cm long, scales with a persistent prickle .....7.
P. elliotti.
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6. Needles usually 11 cm or less long; fascicle sheath 7 mm or less long.
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8. Bark of branches orange to orange-brown; cone scales usually unarmed
or with a minute prickle .....8. P.
sylvestris.
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8. Bark of branches reddish-brown, gray, or black; cone scales usually
armed with a prickle.
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9. Recently mature seed cones light brown and lustrous; scales thick, armed
with a very broad, stout, upwardly curved prickle; needles stiff .....9.
P. pungens.
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9. Recently mature seed cones dull brown or gray; scales thin, usually
armed with a slender, weak, or stout prickle; needles flexible.
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10. Bark of small branches loose, reddish-brown, flaking off and showing
orange-tinged inner bark; 3-needle fascicles often present .....10.
P. echinata.
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10. Bark of small branches smooth, gray or brownish-gray; only 2-needle
fascicles present.
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11. Bark of trunk relatively smooth, not plated; seed cones with weak or
deciduous prickles; tree of moist, fertile soils .....11.
P. glabra.
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11. Bark of trunk plated; seed cones with persistent, slender prickles;
tree of dry or well-drained, sandy or sterile soils.
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12. Needles twisted, stout; seed cones sessile, with long, slender prickles
.....12. P. Virginiana.
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12. Needles not twisted, or slightly so, slender; seed cones short-stalked,
with short, stout prickles .....13.
P. clausa.