Arborvitae
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 Thuja standishii foliage and cones
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Thuja koraiensis |
Arborvitae' is the common name for any of the coniferous evergreen trees or shrubs comprising the genus Thuja (pronounced "thoo-ya" or "thoo-ja") in the cypress family, Cupressaceae. There are five species in the genus, two native to North America and three from Eastern Asia. Some are colloquially known as cedars, such as the western redcedar, Thuja plicata, one of the largest trees in total volume in the world. (However, the "true cedars" comprise comprising trees in the genus Cedrus.)
The name arborvitae comes from the Latin for "tree of life."
importance
Overview
Arborvitae (Thuja) is a type of conifer. The conifers comprise division Pinophyta (also known as division Coniferae), one of 13 or 14 division-level taxa within the Plant Kingdom (Plantae). They are cone-bearing seed plants (specifically gymnosperms) with vascular tissue. All living conifers are woody plants, the great majority being trees with just a few being shrubs. Typical examples of conifers include cedars, cypresses, firs, junipers, pines, redwoods, spruces, and yews. As gymnosperms, conifers bear their seeds "naked"; not covered by an ovary. The other type of seed plants, the angiosperms (flowering plants), cover their seeds by including them in a true fruit. All living conifers are woody plants, and most are trees, the majority having monopodial growth form (a single, straight trunk with side branches) with strong apical dominance (the truck is dominant over the branches).
Arbovitae belong to the cypress family, Cupressaceae. This is a conifer family with worldwide distribution, including about 27 to 30 genera with about 130-140 species. The bark of mature trees is commonly orange- to red- brown and of stringy texture, often flaking or peeling in vertical strips, but smooth, scaly or hard and square-cracked in some species. The leaves are arranged either spirally, in decussate pairs (opposite pairs, each pair at 90° to the previous pair) or in decussate whorls of 3 or 4, depending on the genus. On young plants, the leaves are needle-like, becoming small and scale-like on mature plants of many (but not all) genera; some genera and species retain needle-like leaves throughout their life. Most are evergreen with the leaves persisting 2-10 years, but three genera (Glyptostrobus, Metasequoia, Taxodium) are deciduous or include deciduous species. The seeds are mostly small and somewhat flattened, with two narrow wings, one down each side of the seed; rarely (e.g. Actinostrobus) triangular in section with three wings; in some genera (e.g. Glyptostrobus, Libocedrus) one of the wings is significantly larger than the other, and in some others (e.g. Juniperus, Microbiota, Platycladus, Taxodium) the seed is larger and wingless. The pollen cones are more uniform in structure across the family, 1-20 mm long, with the scales again arranged spirally, decussate (opposite) or whorled, depending on the genus;
The Cupressaceae family is notable for including the largest, tallest, and stoutest individual trees in the world, and also the second longest lived species in the world. The largest is the Giant Sequoia (1486.9 m³ trunk volume), the tallest is the Coast Redwood (115.55 meters tall), the stoutest is the Montezuma Cypress or Ahuehuete (11.42 meters in diameter), and the second oldest is the Alerce (3622 years).
Description
The thuja can grow 3-5 feet (1-1.5meters) per year and can obtain heights of nearly 50 feet (15 meters). Amongst its many uses is the ability to create a natural privacy fence in a very short time.
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, 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 wood of Thuja plicata is commonly used for guitar soundboards.
The foliage of thujas is rich in Vitamin C, and was used by Native Americans and early European explorers as a cure for scurvy.
Oil of thuja is often quoted as an herbal remedy to be used topically to aid in the treatment of HPV, genital or common warts. However, clinical evidence for this action is lacking.
Thuja is a popular homeopathic remedy used to treat a variety of psychological and physiological conditions.
- Largest trees
The largest trees in total volume are those that are tall, of large diameter, and in particular, which hold a large diameter high up the trunk. Measurement is very complex, particularly if branch volume is to be included as well as the trunk volume, so measurements have only been made for a small number of trees, and generally only for the trunk. No attempt has ever been made to include root volume.
The top four species measured so far are (Gymnosperm Database):
- Giant Sequoia Sequoiadendron giganteum: 1489 m³, General Sherman tree
- Coast Redwood Sequoia sempervirens: 1045 m³, Del Norte Titan tree
- Western Redcedar Thuja plicata: 500 m³, Quinault Lake Redcedar
- Kauri Agathis australis: 400 m³, Tane Mahuta tree (total volume, including branches, 516.7 m³)
However, the Alerce Fitzroya cupressoides, as yet unmeasured, may well slot in at third or fourth place, and Montezuma Cypress Taxodium mucronatum is also likely to be high in the list. The largest broadleaf tree is an Australian Mountain Ash, the “El Grande” tree of about 380 m³ in Tasmania.
Species of Thuja
- Thuja koraiensis - Korean Thuja
- Thuja occidentalis - Eastern Arborvitae, Northern Whitecedar
- Thuja plicata - Western Redcedar
- Thuja standishii - Japanese Thuja
- Thuja sutchuenensis - Sichuan 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.
External links
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