Thuja

Linnaeus 1753, p. 1002

Common names

Arborvitae, thuya, cédre (Chambers 1993), ya bai shu (Chinese; Fu et al. 1999).

Taxonomic notes

A generally-accepted genus of five species:

• T. koraiensis
• T. occidentalis
• T. plicata
• T. standishii
• T. sutchuenensis

Both morphological and molecular data show its close alliance to Thujopsis and Chamaecyparis.

Description

Evergreen, monoecious trees or shrubs. Branchlets in fan-shaped, flattened sprays. 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-)6-10(-16) microsporophylls, each with 2-4 pollen sacs. Seed cones maturing and opening first year, terminal, solitary, cone scales in 4-6 pairs, 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 1-3 per scale, lenticular, with 2 lateral, narrow wings. Cotyledons 2 x = 11" (Chambers 1993, Fu et al. 1999). The following key is provided by Fu et al. (1999):

1a.	Leaves obtuse at apex, rarely subacute.
2a.	Facial leaves without a gland; young branchlets not glaucous	T. sutchuenensis
2b.	Facial leaves with a gland; young branchlets ± glaucous	T. koraiensis
1b.	Leaves subacute to acuminate at apex.
3a.	Leaves acuminate at apex; lateral leaves longer than facial leaves, apex straight	T. plicata
3b.	Leaves acute or subabcute at apex, lateral leaves slightly shorter than or as long as facial leaves, apex incurved.
4a.	Facial leaves with a conspicuous abaxial gland	T. occidentalis
4b.	Facial leaves without a gland	T. standishii

Range

North America, E Asia (Chambers 1993).

Big tree

Western redcedar, Thuja plicata, is far larger than the other species.

Oldest

Few or no data exist for the three Asian species, but Thuja plicata is clearly the oldest of the two North American species.

Dendrochronology

Considerable work has been done with Thuja plicata and Thuja occidentalis, and Thuja standishii has been investigated as well. See the species accounts for details.

Ethnobotany

The common name arborvitae is Latin for "tree of life" (17th cent.) because resins of these trees were used medicinally in western Europe. Effects include increasing blood pressure and reducing fever. The wood is reddish, light, and durable. Some of the larger species are valuable timber trees. The smaller species are cultivated in gardens and as wind screens for more tender plants.

Thuja plicata is extraordinarily significant to native peoples in its home range. The other species are less so.

Observations

See the species accounts.

Remarks

'Thuya'; was a Greek name for some evergreen, resinous trees (Chambers 1993).

Citations

See also

Farjon 2005.