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2. Thuja Linnaeus, Sp. Pl. 2: 1002. 1753.
崖柏属 ya bai shu
Trees or shrubs evergreen, monoecious; branchlets arranged in a plane, flattened. Leaves 4-ranked, scalelike, base decurrent only on leading branchlets, dimorphic along branchlets: facial pairs obovate-rhombic; lateral pairs boat-shaped, ridged abaxially, less than 4 mm, overlapping facial pairs, without conspicuous, white stomatal bands abaxially. Pollen cones with (4 or)6-10(-16) microsporophylls, each with (2 or)3 or 4 pollen sacs. Seed cones terminal, solitary, dehiscent when mature in 1st year; cone scales 8 or 10, decussate, flat, only middle, larger 2 or 3 pairs fertile, each fertile scale bearing 1 or 2 seeds; free bract apex a very short mucro. Seeds flat, with 2 lateral, narrow wings. Cotyledons 2.
Five species: E Asia, E and W North America; five species (one endemic, three introduced) in China.
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| 1 |
Leaves obtuse at apex, rarely subacute. |
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(2) |
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Leaves subacute to acuminate at apex. |
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(3) |
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| 2 (1) |
Facial leaves without a gland; young branchlets not glaucous |
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1 Thuja sutchuenensis |
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Facial leaves with a gland; young branchlets ± glaucous |
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2 Thuja koraiensis |
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| 3 (1) |
Leaves acuminate at apex; lateral leaves longer than facial leaves, apex straight |
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3 Thuja plicata |
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Leaves acute or subabcute at apex, lateral leaves slightly shorter than or as long as facial leaves, apex incurved. |
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(4) |
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| 4 (3) |
Facial leaves with a conspicuous abaxial gland |
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4 Thuja occidentalis |
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Facial leaves without a gland |
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5 Thuja standishii |
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Lower Taxa
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