Thuja ( THEW-yə) is a genus of coniferous trees or shrubs in the cypress family, Cupressaceae. There are five species, two native to North America and three native to eastern Asia. The genus is most closely related to Thujopsis. Members are commonly known as arborvitaes (from the Latin term for 'tree of life'), thujas, or New World cedars.
Description
Foliage of the cultivar 'Rheingold'
Thuja are coniferous trees that grow up to 10 to 200 feet (3 to 61 metres) tall, with stringy-textured reddish-brown bark. The shoots are flat, with side shoots only in a single plane. The leaves are scale-like and 1 to 10 mm (0.039 to 0.394 in) 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 to 2 cm (0.39 to 0.79 in) 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.
The species in the genus grow 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-bearing sporophylls. Seed cones are ellipsoid, typically 9 to 14 mm (0.35 to 0.55 in) long, and mature and open the first year. The thin woody cone scales number from 4-6 pairs and are persistent and...
