Thuja occidentalis

Thuja occidentalis
Thuja occidentalis foliage and cones
Conservation status
Least Concern (IUCN 2.3)
Scientific classification
Kingdom:	Plantae
Division:	Pinophyta
Class:	Pinopsida
Order:	Pinales
Family:	Cupressaceae
Genus:	Thuja
Species:	T. occidentalis
Binomial name
Thuja occidentalis L.

Thuja occidentalis (Eastern Arborvitae, Northern Whitecedar) is an evergreen coniferous tree, in the cypress family Cupressaceae, which is widely cultivated for use as an ornamental plant. The endemic occurrence of this species is a north-eastern distribution in North America. It is thought to be the first tree of that region to be cultivated in Europe.

Description

An evergreen tree with fan-like branches and scaly leaves. Unlike the closely related species, Thuja plicata (Western Redcedar), it is only a small tree. Growing to a height of 10-20 m tall with a 0.4 m trunk diameter, exceptionally to 30 m tall and 1.6 m diameter, the tree is often stunted or prostrate. The bark is red-brown, furrowed and peels in narrow, longitudinal strips. The foliage forms in flat sprays with scale-like leaves 3-5 mm long. The cones are slender, yellow-green ripening brown, 10-15 mm long and 4-5 mm broad, with 6-8 overlapping scales. The branches may take root if the tree falls.^[1]

Eastern white-cedars found to be growing on cliff faces in Southern Ontario are the oldest trees in Eastern North America and all of Canada, growing to ages in excess of 1653 years old.^[2]

Distribution

Native to the northeastern U.S. and southeastern Canada, from central Saskatchewan east to New Brunswick, and south to eastern Tennessee in the Appalachian Mountains.

Naming and taxonomy

The species was first described by Carolus Linnaeus in 1753, the name remains current. Common names include Eastern Arborvitae, American Arborvitae, Techny Arborvitae, or just Arborvitae, the last particularly in the horticultural trade. This name, arbor vitae, is derived from the tree of life motif - for the supposed medicinal properties of the sap, bark and twigs.^[3] Other names by which it is known include Northern Whitecedar, Eastern Whitecedar or White Cedar, and Swamp Cedar. Thuja occidentalis trees are unrelated to cedars, or to the Australian tree, Melia azedarach, also known as White Cedar. A large number of names for cultivars are used by horticulturalists.

Ecology

T. occidentalis growing out of a rocky ledge, Potawatomi State Park, Wisconsin, USA

Thuja occidentalis grows naturally in wet forests, being particularly abundant in swamps where other larger and faster-growing trees cannot compete successfully. It also occurs on other sites with reduced tree competition such as cliffs. Although not currently listed as endangered, wild Thuja occidentalis populations are threatened in many areas by high deer numbers; deer find the soft evergreen foliage a very attractive winter food, and strip it rapidly. The largest known is 34 m tall and 175 cm diameter, in South Manitou Island within Leelanau County, Michigan.

It can be a very long-lived tree in certain conditions, with notably old specimens growing on cliffs where they are inaccessible to deer and wildfire; the oldest known living specimen is just over 1,100 years old, but a dead specimen with over 1,650 growth rings has been found.^[4] These very old trees are, despite their age, small and stunted due to the difficult growing conditions. The Witch Tree, a T. occidentalis growing out of a cliff face on Lake Superior in Minnesota, was described by a French explorer as being a mature tree in 1731; it is still alive today.

Uses

A trimmed Eastern Arborvitae hedge

Thuja occidentalis is widely used as an ornamental tree, particularly for screens and hedges. Over 300 cultivars exist, with some of the more common ones being: 'Degroot's Spire', 'Ellwangeriana', 'Hetz Wintergreen', 'Lutea', 'Rheingold', 'Smaragd' (a.k.a. 'Emerald Green'), 'Techny', and 'Wareana'. It was introduced into Europe as early as 1540 and is widely cultivated now, especially in parks and cemeteries.

Northern white cedar is commercially used for rustic fencing and posts, lumber, poles, shingles and in the construction of log cabins, ^[5] White cedar is the preferred wood for the structural elements, such as ribs and planking, of birchbark canoes and the planking of wooden canoes.^[6]

The foliage of thuja is rich in Vitamin C and is believed to be the annedda which cured the scurvy of Jacques Cartier and his party in the winter of 1535–1536.^[5] Due to the neurotoxic compound thujone, internal use can be harmful and is not recommended.

The essential oil within the plant has been used for cleansers, disinfectants, hair preparations, insecticides, liniment, room sprays, and soft soaps. There are some reports that the Ojibwa made a soup from the inner bark of the soft twigs. Others have used the twigs to make teas to relieve constipation and headache.^[6]

Gallery

Leaves on an Eastern Arborvitae

Trunk

Botanical illustration from a 1913 Flora

References

Wikimedia Commons has media related to: Thuja occidentalis

General references

1. Conifer Specialist Group (1998). Thuja occidentalis. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
2. Gymnosperm Database: Thuja occidentalis
3. Borealforest.org: Thuja occidentalis