Western redcedar

The tree

Most authorities write the English name as 'western redcedar' to indicate that it is not a true cedar (Cedrus). It is the largest species in the genus Thuja, growing up to 70 metres (230 ft) tall and 7 m (23 ft) in diameter. The species ranges over a Coast Range-Cascade Range segment from southeastern Alaska to northwestern California and a Rocky Mountains segment from British Columbia to Idaho and Montana. The foliage forms flat, pendant sprays of overlapping scale-like leaves. The epithet plicata means "folded" and refers to the shape of the leaves. It has been introduced to cool temperate areas in other parts of the world, such as Northern Europe and New Zealand.

Wood and heartwood

The wood is aromatic and rot-resistant and is used for applications such as shingles and siding. Tropolones concentrated in the heartwood give the wood its decay resistance and contribute to its distinctive aroma. The heartwood contains thujaplicins, which serve as natural fungicides that prevent the wood from rotting. This effect lasts around a century even after the tree is felled, but thujaplicins are found only in older trees. Thujaplicins were discovered in the mid-1930s and purified from the heartwood of Thuja plicata. Plicatic acid, a heartwood constituent, is believed to be the main irritant and contact allergen behind occupational asthma in woodworkers exposed to the wood dust.

Cultural uses

Indigenous peoples of the Pacific Northwest use the wood of this species for many purposes, such as building canoes, totem poles and tools. They harvest the bark and process it into a fiber used for rope, baskets, clothing and rain hats.

Leaf oil

The essential oil of the leaves contains α-thujone, β-thujone, fenchone, sabinene, terpinen-4-ol and beyerene. In samples from the Cascade Range of Oregon, the major components were α-thujone (67.1-74.6%), β-thujone (7.8-9.3%), terpinen-4-ol (2.7-4.4%) and sabinene (1.1-3.5%). Gas chromatography of these oils identified 91 components, which accounted for 98.7% of the composition in each sample. The essential oil compositions of T. plicata are very similar regardless of the collection site. Thujone is a ketone and a monoterpene that occurs predominantly in two diastereomeric forms, (-)-α-thujone and (+)-β-thujone. In western redcedar, thujone is derived exclusively from the (+)-trans-sabinol intermediate. Thujones are competitive antagonists of the GABA A receptor and have no pharmacological use because of their high toxicity and convulsive activity.

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Related: Australian Blue Cypress · Cedar · Cedarwood · Cedrene · Cedrol · Cedryl Acetate · Cypress · False Cypress