Flora of the Southeastern United States
2022 Edition

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Key to Pinus

1 Needles 5 in each bundle; each needle with 1 vascular bundle (visible in X-section, by breaking or cutting a needle); [subgenus Strobus, section Quinquefoliae, subsection Strobus]
1 Needles 2-3 (-4) in each bundle; each needle with 2 vascular bundles; [subgenus Pinus].
..2 Bracts and bud scales fimbriate; sheath > 1.3 cm long; needles 20-50 cm long, in bundles of 3 (-4); twigs about 1 cm in diameter; [subgenus Pinus, section Trifoliae, subsection Australes]
..2 Bracts and bud scales entire or edged with hairs, but not fimbriate; sheath < 1.5 cm long; needles (2-) 3-30 cm long, in bundles of 2-4; twigs < 1 cm in diameter.
....3 Needles in bundles of 3, or 2 and 3, or 3 and 4 (predominantly or at least substantially in 3's); [subgenus Pinus, section Trifoliae, subsection Australes].
......4 Needles in bundles of 3 (rarely with a few bundles of 2, 4, or 5).
........5 Cones distinctly longer than broad when open or closed, 5-13 cm long; needles mostly (10-) 12-23 (-28) cm long, 0.7-1.5 mm wide; buds not resinous (or only slightly so); trunks not producing adventitious sprouts (epicormic sprouting)
........5 Cones about as broad as long, 3-6 (-9) cm long; needles (4-) 7-20 cm long, 1.5-2.0 mm wide; buds resinous; trunks commonly producing adventitious sprouts (epicormic sprouting), especially in response to fire.
..........6 Needles (4-) 7-10 (-15) cm long, persisting only 2 years; cones opening at maturity, not serotinous; [ridges, slopes, bottomlands, and bogs of the Mountains and Piedmont, northwards in Coastal Plain acid uplands and wetlands]
..........6 Needles (10-) 16-20 cm long, persisting 3-4 years; cones serotinous; [pocosins, savannas, and other wetlands of the Coastal Plain]
......4 Needles in bundles of 2 and 3.
............ 7 Needles 3-11 (-13) cm long.
............ ..8 Needles 5-11 (-13) cm long; prickles on cones 1-3 mm long, slender (< 1 mm wide at base of prickle); cones 4-6 (-7) cm long.
............ ..8 Needles 3-6 (-8) cm long; prickles on cones 3-8 mm long, stout (> 1 mm wide at base of prickle); cones (4-) 6-10 cm long.
............ 7 Needles 17-30 cm long.
............ ....9 Leaves mostly in bundles of 2 (and some bundles of 3); seedlings with a grass stage; resin canals 3-9 per leaf; base of open cone rounded; [of peninsular FL]
............ ....9 Leaves mostly in bundles of 3 (and some bundles of 2); seedlings lacking a grass stage; resin canals 3-5 per leaf; base of open cone truncate; [more widespread]
....3 Needles in bundles of 2 only.
............ ......10 Needles slender to somewhat stout, 0.5-1.2 mm wide.
............ ........11 Needles 10-17 cm long; branches brittle; spring shoots with a single node, with 1 whorl of branches; [subgenus Pinus, section Pinus, subsection Pinus]
............ ........11 Needles 2-13 cm long; branches flexible; spring shoots usually with several nodes (several whorls of branches).
............ ..........12 Needles 2-8 cm long, generally twisted; cones either opening at maturity, not serotinous, the scales bearing prominent, slender prickles 2-5 mm long, or serotinous and unarmed; [subgenus Pinus, section Trifoliae, subsection Contortae].
............ ............ 13 Needles 2-3.5 cm long, not twisted, curved; cones serotinous, unarmed; leaf sheaths < 2.5 mm long
............ ............ 13 Needles 2-8 cm long, generally twisted, straight; cones opening at maturity, not serotinous, the scales bearing prominent, slender prickles 2-5 mm long; leaf sheaths > 2.5 mm long
............ ..........12 Needles 5-13 cm long, twisted or not; cones opening at maturity or serotinous, the scales bearing prominent, short, stout prickles or minute, deciduous prickles, and also with a faint to conspicuous horizontal ridge.
............ ............ ..14 Anthers dark orange; bark flaky, the laminated layers sloughing off in a manner typical of a pine; [native in xeric sands, also sometimes planted in pine tree farms]; [subgenus Pinus, section Trifoliae, subsection Contortae]
............ ............ ..14 Anthers yellow; bark tight, closely ridged, not sloughing off, reminiscent of a hardwood; [mesic to fairly wet, fertile soils]; [subgenus Pinus, section Trifoliae, subsection Australes]
............ ......10 Needles stout, 1.3-2.5 mm wide.
............ ............ ....15 Needles 15-25 cm long; cones 8-22 cm long; needles 1.5-2.5 mm wide; [naturalized on barrier islands]; [subgenus Pinus, section Pinus, subsection Pinaster]
............ ............ ....15 Needles 3-16 cm long; cones 3-9 cm long; needles 1.3-2 mm wide; [collectively widespread].
............ ............ ......16 Needles 7-16 cm long; cones 4-6 cm long, each scale bearing a small depressed mucro; [introduced]; [subgenus Pinus, section Pinus, subsection Pinus].
............ ............ ........17 Buds light brown, resinous; [introduced, often planted inland]
............ ............ ........17 Buds white, not resinous; [introduced tree, usually planted only on Coastal Plain barrier islands]
............ ............ ......16 Needles 3-6 (-8) cm long; cones either 6-9 cm long with each scale bearing a stout, woody spine, or 3-6 cm long and unarmed; [native tree of the Mountains and upper Piedmont or introduced trees south to MD and WV].
............ ............ ..........18 Cones (4-) 6-9 cm long with each scale bearing a stout, woody spine; [native tree of the Mountains and upper Piedmont]; [subgenus Pinus, section Trifoliae, subsection Australes]
............ ............ ..........18 Cones 3-6 cm long, unarmed; [introduced trees south to MD and WV].
............ ............ ............ 19 Needles 2-3.5 cm long; cone appressed upward against the stem, strongly asymmetrical; leaf sheaths < 2.5 mm long; [subgenus Pinus, section Trifoliae, subsection Contortae]
............ ............ ............ 19 Needles 3-7 cm long; cone reflexed downward against the stem; leaf sheaths > 2.5 mm long; [subgenus Pinus, section Pinus, subsection Pinus]