Thuja Wednesday, July 1, 2009

Thuja
Thuja standishii foliage and cones
Scientific classification
Kingdom: Plantae Division: Pinophyta Class: Pinopsida Order: Pinales Family: Cupressaceae Genus: Thuja L.
Species
Thuja koraiensis Thuja occidentalis Thuja plicata Thuja standishii Thuja sutchuenensis

Thuja (pronounced /ˈthu·ja/ or /ˈθjuːdʒə/)^[1] is a genus of coniferous trees in the Cupressaceae (cypress family). There are five species in the genus, two native to North America and three native to eastern Asia.^[2][3]

They are commonly known as arborvitae (from Latin for tree of life) or thujas; several species are widely known as cedar but because they are not true cedars (Cedrus) it has been recommended to call them redcedars or whitecedars.^[4]

They are evergreen trees growing to 10–60 m tall, with stringy-textured reddish-brown bark. The shoots are flat, with side shoots only in a single plane. The leaves are scale-like 1–10 mm long, except young seedlings in their first year, which have needle-like leaves. The scale leaves are arranged in alternating decussate pairs in four rows along the twigs. The male cones are small, inconspicuous, and are located at the tips of the twigs. The female cones start out similarly inconspicuous, but grow to about 1-2 cm long at maturity when 6–8 months old; they have 6-12 overlapping, thin, leathery scales, each scale bearing 1–2 small seeds with a pair of narrow lateral wings.^[2]

Species

• Thuja koraiensis - Korean Thuja
• Thuja occidentalis - Eastern Arborvitae, Northern Whitecedar
• Thuja plicata - Western Redcedar
• Thuja standishii - Japanese Thuja
• Thuja sutchuenensis - Sichuan Thuja

Description

The five species in the genus Thuja are small to large evergreen trees with flattened branchlets. The leaves are arranged in flattened fan shaped groupings with resin-glands, and oppositely grouped in 4 ranks. The mature leaves are different from younger leaves, with those on larger branchlets having sharp, erect, free apices. The leaves on flattened lateral branchlets are crowded into appressed groups and scale-like and the lateral pairs are keeled. The solitary flowers are produced terminally. Pollen cones with 2-6 pairs of 2-4 pollen sacked sporophylls. Seed cones ellipsoid, typically 9-14mm long, they mature and open the first year. The thin woody cone scales number from 4-6 pairs and are persistent and overlapping, with an oblong shape, they are also basifixed. The central 2-3 pairs of cone scales are fertile. The seed cones produce 1 to 3 seeds per scale, the seeds are lenticular in shape and equally 2 winged. Seedlings produce 2 cotyledons. ^[5][6]

A hybrid between T. standishi and T. plicata has been named as the cultivar Thuja 'Green Giant'.

Another very distinct and only distantly related species, formerly treated as Thuja orientalis, is now treated in a genus of its own, as Platycladus orientalis. The closest relatives of Thuja are Thujopsis dolabrata, distinct in its thicker foliage and stouter cones, and Tetraclinis articulata (Greek θύια, θύα, formerly classed in the genus and after which Thuja is named), distinct in its quadrangular foliage (not flattened) and cones with four thick, woody scales.

Ecology

Thuja species are used as food plants by the larvae of some Lepidoptera species including Autumnal Moth, The Engrailed and Juniper Pug. The foliage is also readily eaten by deer, and where deer population density is high, can adversely affect the growth of young trees and the establishment of seedlings.^[7]

Uses

They are widely grown as ornamental trees, and extensively used for hedges. A number of cultivars are grown and used in landscapes.^[8][9] Usually, homeowners will plant them as privacy trees between them and their neighbors. The cultivar 'Green Giant' is popular as a very vigorous hedging plant, growing up to 80 cm/year when young.^[10]

The wood is light, soft and aromatic. It can be easily split and resists decay. The wood has been used for many applications from making chests that repel moths to shingles. Thuja poles are also often used to make fence posts and rails. The wood of Thuja plicata is commonly used for guitar soundboards. ^[11]

Oil of thuja contains the terpene thujone which has been studied for its GABA receptor antagonistic, with potentially lethal properties. ^[12]

The natives of Canada used the needles of the Thuja occidentalis (Eastern White Cedar) to make a tea that has been shown to contain 50 mg of vitamin C per 100 grams. This helped fight off scurvy.

References

1. ^ Sunset Western Garden Book, 1995:606–607
   "Thuja". Oxford English Dictionary. Oxford University Press. 2nd ed. 1989.
2. ^ ^{a b} Farjon, A. (2005). Monograph of Cupressaceae and Sciadopitys. Royal Botanic Gardens, Kew. ISBN 1-84246-068-4
3. ^ Gymnosperm Database: Thuja
4. ^ Kelsey, H. P., & Dayton, W. A. (1942). Standardized Plant Names, second edition. American Joint Committee on Horticultural Nomenclature. Horace McFarland Company, Harrisburg, Pa.
5. ^ Flora of North America Editorial Committee. 1993. Pteridophytes and gymnosperms. Flora of North America north of Mexico, v. 2. New York: Oxford University Press. ISBN 0195082427 Page 410.
6. ^ Henry A Gleason. New Britton and Brown Illustrated flora of Eastern North America and adjacent Canada Vol 1, The Pteridophya, Gymnospermae and Monocotyledoneae. Hafner Press, pp 58-67.
7. ^ Stein, W.I. 1997. Ten-year survival and growth of planted Douglas-fir and western redcedar after seven site-preparation treatments. Western-Journal-of-Applied-Forestry 12(3): 74-80.
8. ^ Thuja plicata
9. ^ Thuja occidentalis
10. ^ U.S. National Arboretum: Gardens: FAQs: 'Green Giant' Arborvitae
11. ^ Bucur, Voichita. 1995. Acoustics of wood. Boca Raton: CRC Press.
12. ^ Höld KM, Sirisoma NS, Ikeda T, Narahashi T, Casida JE (2000). "Alpha-thujone (the active component of absinthe): gamma-aminobutyric acid type A receptor modulation and metabolic detoxification". Proc. Natl. Acad. Sci. U.S.A. 97 (8): 3826–31. doi:10.1073/pnas.070042397. PMID 10725394.