Flora of the Southeastern United States
2022 Edition

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Key to Cupressaceae

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; [subfamily Cupressoideae].
......4 Leaves deciduous; [subfamily Sequoioideae]
......4 Leaves evergreen; [subfamily Cupressoideae].
........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 Callitroideae]
..........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]