Editing Thuja (section)

==Description==
[[File:Thuja 'Rheingold' in Autumn.JPG|thumb|Foliage of the cultivar 'Rheingold']]
''Thuja'' are [[evergreen]] [[tree]]s growing from {{convert|10|to|200|ft|m|0|abbr=off}} tall, with stringy-textured reddish-brown [[Bark (botany)|bark]]. The shoots are flat, with side shoots only in a single plane. The leaves are scale-like and {{convert|1|to|10|mm|abbr=on}} 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 [[conifer cone|cones]] start out similarly inconspicuous, but grow to about {{convert|1|to|2|cm|abbr=on}} long at maturity when 6–8 months old; they have 6-12 overlapping, thin, leathery scales, each scale bearing 1–2 small [[seed]]s with a pair of narrow lateral wings.<ref name=farjon/>

The five species in the genus ''Thuja'' are small to large evergreen trees with flattened [[branchlet]]s. 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 {{convert|9|to|14|mm|abbr=on}} 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.<ref>{{eFloras |1 |family=Cupressaceae |first=Kenton L. |last=Chambers}}</ref><ref>{{cite encyclopedia |first=Henry A. |last=Gleason |encyclopedia=New Britton and Brown Illustrated Flora of Eastern North America and Adjacent Canada |title=Coniferae |url=https://archive.org/details/newbrittonbrowni01glea/page/58/mode/1up |volume=1: The Pteridophya, Gymnospermae and Monocotyledoneae |publisher=Hafner Press |pages=58–67}}</ref>

[[File:Riesenlebensbaumstmrp.jpg|thumb|right|''T. plicata'' bark, foliage]]
[[File:The Kalaloch Cedar - Flickr - rachel thecat.jpg|thumb|right|[[Old growth]] ''T. plicata'', [[Olympic Peninsula]], USA]]
[[File:Podlaskie - Suprasl - Kopna Gora - Arboretum - Thuja occidentalis 'Smaragd' - plant.JPG|thumb|right|Cultivars of ''T. occidentalis'' in an arboretum]]
[[File:Thuja occidentalis 'EuropeGold'-201601-JAPAN.jpg|thumb|''Thuja occidentalis'' cultivar 'EuropeGold']]

A [[Hybrid (biology)|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|Platycladus orientalis]]''. The closest relatives of ''Thuja'' are ''[[Thujopsis|Thujopsis dolabrata]]'', distinct in its thicker foliage and stouter cones, and ''[[Tetraclinis articulata]]'' ([[Ancient Greek]] {{lang|grc|θυία}} or {{lang|grc|θύα}}, 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]].<ref>{{Cite NIE|wstitle=Arbor Vitæ}}</ref>