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Keyed in multiple places:

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Key to Cupressaceae

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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]

Key B3: gymnosperm trees and shrubs with scale or needle leaves

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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 < 12 mm in diameter
....3 Leaves linear, 15-45 mm long; mature female “cones” fleshy and drupe-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 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
............ ......10Cone” 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
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