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 Thuja subsp. var.  Arborvitae, Red Cedar, White cedar
Thuja occidentalis
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Lifespan: perennial
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Cupressaceae > Thuja var. ,

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Thuja (pronounced /ˈθuːdʒə/ or Template:IPA-en)[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] The genus is monophyletic and sister to Thujopsis.

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 from 10 to 60 ft 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]

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. With the exception of T. plicata, the lateral leaves are shorter than the facial leaves (Li et al 2005). 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'.

Standard Cyclopedia of Horticulture

Thuja (Thya or Thyia, an ancient Greek name for a resinous tree or shrub). Also spelled Thuya or Thuia. Including Biota. Pinaceae. Arbor-vitae. Ornamental woody plants, grown for their handsome evergreen foliage and formal habit.

Resiniferous trees with short horizontal much ramified branches; the flattened branchlets arranged frond-like: lvs. decussate, scale-like, appressed, usually glandular on the back: fls. monoecious, globose, small, terminal on short branchlets, staminate yellow and consisting of usually 6 opposite stamens each with 2-4 anther-cells; pistillate consisting of 8-12 scales in opposite pairs, of which only the middle ones, or in the section Biota the lower ones, are fertile, each scale with 2 ovules inside at the base: strobiles globose-ovate to oval-oblong, with 2 seeds under the fertile scales.— Five species occur in N. Amer., E. and Cent. Asia. The wood is light and soft, brittle and rather coarse-grained, durable in the soil; it is much used for construction, cabinet-making, and in cooperage. T. occidentalis contains a volatile oil, and thujin and is sometimes used medicinally.

The thujas are trees of narrow pyramidal habit, but low and bushy in many of the numerous garden forms, with much ramified branches, the branchlets arranged frond-like, flattened and clothed with small scale-like leaves; the fruit is a small strobile or cone not exceeding 1 inch in length. The well-known T. occidentalis is hardy North; and also T. Standishii, T. plicata, and several forms of T. orientalis are hardy as far north as Massachusetts. Thujas are favorites for formal gardens. They are all of regular symmetrical habit. Their numerous garden forms vary greatly in habit and in color of foliage. For planting as single specimens in parks they are mostly too stiff and formal, but they are well suited for massing on borders of streams or lakes. The most beautiful and the most rapidly growing species is T. plicata. Thujas are well adapted for hedges and windbreaks (see Gn.M.2:15). They bear pruning well and soon form a dense hedge. They thrive best in somewhat moist, loamy soil and are easily transplanted. Propagation is by seeds sown in spring. The varieties, especially those of T. occidentalis, are usually propagated by cuttings taken late in summer and kept during the winter in a cool greenhouse or frame; also by grafting on seedling stock in summer or early in spring in the greenhouse. The varieties of T. plicata and T. orientalis are usually grafted, since they do not grow readily from cuttings, except the juvenile forms of the latter, as var. decussata and var. meldensis. Consult Retinispora.

T. dolobrata, Linn.-Thujopsis dolobrata. CH

The above text is from the Standard Cyclopedia of Horticulture. It may be out of date, but still contains valuable and interesting information which can be incorporated into the remainder of the article. Click on "Collapse" in the header to hide this text.


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