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Thuja standishii.jpg
Thuja standishii foliage and cones
Scientific classification
Kingdom: Plantae
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Cupressaceae
Genus: Thuja

Thuja koraiensis
Thuja occidentalis
Thuja plicata
Thuja standishii
Thuja sutchuenensis

Thuja (pronounced Thuya) is a genus of coniferous trees in the Cupressaceae (cypress family). There are five species in the genus, two native to North America and three from Eastern Asia. They are commonly known as arborvitae (from Latin for tree of life), due to the evergreen foliage; some are also sometimes known by the incorrect name "cedar" (they are not cedars).

The leaves of Thuja are evergreen and scale-like, except young seedlings, where they are needle-like. The scales are arranged in four rows along the twigs. Thuja species are used as food plants by the larvae of some Lepidoptera species including Autumnal Moth, The Engrailed and Juniper Pug.

The male cones are small and inconspicuous and are located at the tips of the twigs. The female cones start out similarly inconspicuous, but grow to about 1-2 cm long with 6-12 overlapping, thin, leathery scales.

The wood of thujas is light, soft and aromatic. It can be easily split and resists decay. The wood has been used for many applications from making chests that repel moths to shingles. Thuja poles are also often used to make fence posts and rails.

The foliage of thujas is rich in Vitamin C, and are used by Native Americans and early European explorers as a cure for scurvy.

Species of Thuja

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, distinct in its quadrangular foliage (not flattened) and cones with four thick, woody scales.

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