Thuja gigantea japonica (Maxim.) Franch. & Sav.
Thuja japonica Maxim.
Thuja odorata Doi
Thujopsis standishii Gordon
Thuja standishii is an evergreen tree with a broadly pyramidal crown; it can grow up to 30 metres tall. The straight, cylindrical bole is around 60cm in diameter[
The tree produces a valuable timber and is commonly harvested from the wild. It is widely grown as an ornamental in Japan, but less so in other countries[
The protected status in the historical past of this species is assumed to have had a positive effect preventing over-exploitation. However, its valuable timber must have led to some reduction in abundance of mature trees but it is uncertain if this exceeds the thresholds for listing in any threatened category. Presently, there is only limited exploitation. The plant is classified as 'Near Threatened' in the IUCN Red List of Threatened Species(2013)[
The essential oil in this plant contains thujone. Thujone is a GABA receptor antagonist which allows neurons to fire more easily. In larger doses this can cause muscle spasms and convulsions, and can also be toxic to brain, kidney, and liver cells.
There has been a lot of negative press regarding thujone, particularly in the mid 19th century when thujone was reported to be more dangerous than alcohol - since shown to be exaggerated; and reports in the 1970’s that it might have a similar effect on the brain to THC (found in cannabis) – since found to be incorrect.
Thujone is probably best known for its use in the alcoholic drink ‘Absinthe’. It is also found in the essential oils of many other plants that are used in herbal medicines and foods, including Arborvitae (Thuja species), some Junipers (Juniperus species), Wormwoods (especially Artemisia absinthium) and Sage (Salvia officinalis). There are some legal restrictions in various countries on the quantity of thujone that can be added to foods and drinks and these vary between countries.
Side effects from consuming thujone can include sleeplessness and anxiety but, unless the pure essential oil is used, the quantity of thujone found in plants is well within safety levels. Pregnant women, however, may be advised to restrict their use of thujone-containing plants.
E. Asia - Japan (Honshu and Hokkaido)
A minor component of mixed montane conifer or conifer-angiosperm forests, often confined to moist rocky precipices facing north - sites which are less suitable for larger trees; at elevations from 500 - 2,000 metres[
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Thuja standishii is native to the subalpine and upper cool temperate forests of central and southern Japan, where it is known to tolerate winter temperatures down to around -20°c[
Plants are tolerant of regular trimming, so long as this does not go back into the old wood[
This species was in the past regarded as one of the 'five trees of Kiso' or 'Tome-ki' (preserved trees) which meant they were the property of the Emperors of the Tokugawa dynasty in the 17th and 18th centuries and not to be used by common people. This practice preserved several forests from overexploitation[
The crushed foliage has a pleasant aroma[
The tree is tolerant of regular light trimming, though should not be cut back into the old wood. It can be grown as a hedge[
The wood of this species is highly prized for special building purposes, e.g. ceilings and panelling, and is also used for furniture, fanlights and clogs (wooden shoes)[
Seed - best sown when ripe in the autumn in a cold frame[
]. Stored seed germinates best if given a short cold stratification[
]. It can be sown in a cold frame in late winter. When they are large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for their first winter. Plant them out into their permanent positions in late spring or early summer, after the last expected frosts.
If growing large quantities of plants, the seed can be sown in an outdoor seed bed in mid spring[
]. Grow the plants on for two years and then plant them out into their permanent positions in late autumn or early spring.
Cuttings of half-ripe wood, 5 - 8cm with a heel, mid summer in a shaded frame. Forms roots by the end of September but it should be overwintered in a frame[
Cuttings of almost ripe wood, 5 - 10cm with a heel, September in a cold frame. Forms roots in the following summer. Plant out in autumn or spring[