Western Red Cedar (Thuja plicata D. Don ex. Lambert)

Abstract

A member of the Cupressaceae family, the genus Thuja comprises five species, two of which are native to North America: Thuja plicata D. Don ex. Lambert (Western red cedar; Fig. 1) and Thuja occidentalis L. (white cedar). The three others are native to Asia: Thuja orientalis L. (Chinese cedar), Thuja standishii (Gord.) Carr. (Japanese thuja) and Thuja koraiensis (Korean thuja). The thujas are evergreen coniferous trees with scale-like leaves pressed closely to the stem. The twigs are flattened, usually in horizontal plane, much branched, forming fan-like sprays. The small scale-like, short-pointed, yellow-green leaves are paired or opposite in four rows, mostly shedding together with the twigs after several years. The reproductive organs are of the pine type, with both male and female organs in separate cones on the same tree. The young cones are tiny and inconspicuous at the end of the twigs, with the sexes usually on different branches. The seedlings have two cotyledons. The basic chromosome number of the genus Thuja is n = 22 (Hosie 1969; Zobel and Talbert 1984). These conifers are also known as “arbor vitae”. Thuja plicata (Western red cedar) covers an extensive area of the west coast of North America, from the south of Alaska to lower California and from the coastal regions of the Pacific Ocean to the Rocky Mountains, where it reaches altitudes of up to 1800 m. It is mainly to be found in areas with high atmospheric humidity. Its growth is optimal in well-structured, deep, fresh, and porous soil, at pH 5–6.5.