Thuja ( ) is a genus of coniferous tree 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. The genus is monophyletic and sister to
Thujopsis. Members are commonly known as
arborvitaes (from the Latin term for ´tree of life´),
thujas, or New World false cedars.
Thuja are evergreen trees growing from 10 to 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 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 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 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 are ellipsoid, typically 9 to long, and 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.
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 (Ancient Greek or , 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.
The genus
Thuja, like many other forms of conifers, is represented by ancestral forms in Cretaceous rocks of northern Europe, and with the advance of time is found to migrate from northerly to more southerly regions, until during the Pliocene period, when it disappeared from Europe.
Thuja is also known in the Miocene beds of the Dakotas.
Phylogeny: | Stull et al. 2021 |
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| label1=Thuja | 1= Source: Wikipedia, article Thuja sp..
Content adapted from Wikipedia, available under the CC BY-SA 4.0 license.
Accessed on 17/07/2026.
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