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| 1 Leaves alternate. |
..2 Leaves 4-sided or nearly circular (terete) in ×-section; [subfamily Taxodioideae] |
| ..2 Leaves distinctly flattened (2-sided). |
| ....3 Leaves evergreen, rigid, > 2 cm long, tapering from near the base to a long-acuminate apex; [subfamily Cunninghamioideae] |
| ....3 Leaves deciduous, flexible, < 2 cm long, parallel-sided, the apex short-acute; [subfamily Taxodioideae] |
| 1 Leaves opposite or whorled. |
| ......4 Leaves deciduous; [subfamily Sequoioideae] |
| ......4 Leaves evergreen. |
| ........5 Plants dioecious, male and female cones on separate plants; mature female cones fleshy and berry-like, with smooth surfaces, indehiscent; branchlets not disposed in one plane, thus bushy and not fan-like; leaves of a branchlet monomorphic; [subfamily Cupressoideae] |
| ........5 Plants monoecious, male and female cones on the same plant; mature female cones woody or leathery, with irregular surfaces, dehiscent; ; branchlets either disposed in one plane, thus flattened and fan-like, or not disposed in one plane, thus bushy and not fan-like; leaves of a branchlet either monomorphic (Callitris, Hesperocyparis) or dimorphic. |
| ..........6 Leaves in whorls of 3; [subfamily Actinostroboideae] |
| ..........6 Leaves opposite (decussate), in 4 ranks; [subfamily Cupressoideae]. |
| ............ 7 Leaves of a branchlet monomorphic; branchlets not disposed in one plane, thus bushy and not fan-like; female cone globose, 20-30 mm in diameter |
| ............ 7 Leaves of a branchlet dimorphic; branchlets disposed in one plane; thus flattened and fan-like; female cone < 12 mm in diameter. |
| ............ ..8 Leaves acute; female cones globose and woody, the hard scales peltate, not imbricate; ultimate branchlets (including the scale leaves) about 1 mm broad |
| ............ ..8 Leaves obtuse; female cones ellipsoid and leathery, the pliable scales basally attached, imbricate; ultimate branchlets (including the scale leaves) about 1.5 mm broad |
| ............ ....9 Branchlets flattened in vertical planes; seeds wingless; [planted tree, sometimes persistent] |
| ............ ....9 Branchlets flattened in horizontal planes; seeds winged; [native tree, but also sometimes planted] |
| 1 Leaves opposite or in whorls of 3. |
| ..2 Longest internodes 2-10 cm long; stems green, Equisetum-like |
| ..2 Longest internodes < 1 cm long; stems green, brown, or tan, not resembling Equisetum. |
| ....3 Leaves scale-like or acicular and <16 mm long; mature cones either dry and cone-like, or fleshy and < 9 mm in diameter |
| ....3 Leaves linear, 15-45 mm long; mature female “cones” fleshy and berry-like, > 15 mm in diameter |
| ......4 Leaf apex acute, but not stiff, pungent, or spinose; midvein obviously raised (use 10× magnification) on the upper surface, that surface flat or nearly so, except for the revolute margins; stomatal bands on the leaf undersurface broad, white, together making up about 3/4 of the width of the leaf; drupe-like 'fruit' 18-25 mm long, brown, brown or brownish-orange and not striped |
| ......4 Leaf apex acuminate, extended into a stiff, pungent spine; midvein not obviously raised on the upper leaf surface, that surface convex-curved; stomatal bands on the leaf undersurface narrow, greenish gray, together making up about 1/4 of the width of the leaf; drupe-like 'fruit' 25-35 mm long, dark-green and also longitudinally striped with paler green, tan, or purple |
| 1 Leaves either alternate, or in fascicles of 2-5 (basally bound by a scarious sheath), or on short shoots in clusters of many 10-60 leaves in apparent whorls. |
| ........5 Leaves either borne in fascicles of 2-5 (basally bound by a scarious sheath) (Pinus) or on short shoots in clusters of many leaves in apparent whorls (Cedrus, Larix) |
| ........5 Leaves alternate. |
| ..........6 Leaves 4-angled in cross-section. |
............ 7 Twigs green |
| ............ 7 Twigs brown or tan |
| ..........6 Leaves distinctly flattened (2-sided) in cross-section. |
| ............ ..8 Leaves (fresh) very soft in texture, seasonally deciduous as twiglets; [primarily Coastal Plain] |
| ............ ..8 Leaves (fresh) stiffer in texture, evergreen; [collectively more widespread]. |
| ............ ....9 Leaves tapering from base to a long-acuminate tip |
| ............ ....9 Leaves with parallel margins for most of their length, or widest near middle and gradually tapering to base and apex, the apex acute, obtuse, or retuse. |
| ............ ......10 Cone dry, brown, and woody at maturity |
| ............ ......10 ”Cone” fleshy, red or purplish at maturity |
| ............ ........11 Seed surrounded by a fleshy scale, appearing drupe-like, this also subtended by a swollen and fleshy receptacle |
| ............ ........11 Seed partially or fully enclosed in a fleshy aril, the subtending receptacle neither swollen nor fleshy |
| ............ ..........12 Leaf apex acuminate, extended into a stiff, pungent spine; midvein not obviously raised on the upper leaf surface, that surface convex-curved; stomatal bands on the leaf undersurface narrow, greenish gray, together making up about 1/4 of the width of the leaf; drupe-like 'fruit' 25-35 mm long, dark-green and also longitudinally striped with paler green, tan, or purple, the leathery exterior fully enclosing the seed |
| ............ ..........12 Leaf apex acute, but not stiff, pungent, or spinose; midvein obviously raised (use 10× magnification) on the upper surface, that surface flat or nearly so, except for the revolute margins; stomatal bands on the leaf undersurface medium to broad, white or whitish-green, together making up about 1/2 or 3/4 of the width of the leaf; drupe-like 'fruit' either 4-7 mm long, red or orange when ripe, with a softly fleshy exterior open at the top (the seed) visible, or 18-25 mm long, brown, brown or brownish-orange and not striped, the fleshy exterior fully enclosing the seed. |
| ............ ............ 13 Stomatal bands on the leaf undersurface broad, white, together making up about 3/4 of the width of the leaf; drupe-like 'fruit' 18-25 mm long, brown, brown or brownish-orange and not striped, the fleshy exterior fully enclosing the seed; leaf resin canal present, below the vascular tissue (break leaf and use 10× magnification); drupe-like 'fruits' clustered on peduncles |
| ............ ............ 13 Stomatal bands on the leaf undersurface medium, whitish-green, together making up about 1/2 of the width of the leaf; drupe-like 'fruit' 4-7 mm long, red or orange when ripe, with a softly fleshy exterior open at the top (the seed) visible; leaf resin canal absent; drupe-like 'fruits' solitary, sessile or nearly so |