''Thuja'' ( ) is a genus of coniferous

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

or shrub in the Cupressaceae (cypress family). There are five species in the genus, two native to North America and three native to eastern

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an are ...

. The genus is monophyletic and sister to ''

Thujopsis ''Thujopsis'' () is a genus of conifers in the cypress family (Cupressaceae), the sole member of which is ''Thujopsis dolabrata''. It is endemic to Japan, where it is named ''asunaro'' (). It is similar to the closely related genus '' Thuja'' (a ...

''. Members are commonly known as arborvitaes (from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

term for 'tree of life'), thujas or cedars.

Description

''Thuja'' are

evergreen In botany, an evergreen is a plant which has foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, whic ...

s growing from 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 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 A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...

start out similarly inconspicuous, but grow to about long at maturity when 6–8 months old; they have 6-12 overlapping, thin, leathery scales, each scale bearing 1–2 small

seed A seed is an embryonic plant enclosed in a protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, including the gymnosperm and angiospe ...

s with a pair of narrow lateral wings. The five species in the genus ''Thuja'' are small to large evergreen trees with flattened

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