北美香柏种

别名

香柏（通用名），美国侧柏（中国树木分类学），黄心柏木（中国木材学）

Thuja occidentalis, also known as northern white-cedar, eastern white-cedar, or eastern arborvitae, is a coniferous tree in the cypress family, Cupressaceae, which is native to eastern Canada and much of the north-central and northeastern United States. It is widely cultivated as an ornamental plant. It is not to be confused with Juniperus virginiana (eastern red cedar).

Common names

Its additional common names include swamp cedar, American arborvitae, and eastern arborvitae. The name arborvitae is particularly used in the horticultural trade in the United States; it is Latin for 'tree of life' due to the supposed medicinal properties of the sap, bark, and twigs. It is sometimes called white-cedar (hyphenated) or whitecedar (one word) to distinguish it from Cedrus, the true cedars.

Description

Unlike the closely related western red cedar (Thuja plicata), northern white cedar is only a small or medium-sized tree, growing to a height of 15 m (49 ft) tall with a 0.9 m (3.0 ft) trunk diameter, exceptionally to 38 metres (125 ft) tall and 1.8 metres (5.9 ft) diameter. The tree is often stunted or prostrate in less favorable locations. The bark is red-brown, furrowed and peels in narrow, longitudinal strips.

Northern white cedar has fan-like branches and scaly leaves. The foliage forms in flat sprays with scale-like leaves 3–5 millimetres (1⁄8–3⁄16 in) long.

The seed cones are slender, yellow-green, ripening to brown, 9–14 millimetres (3⁄8–9⁄16 in) long and 4–5 millimetres (5⁄32–3⁄16 in) broad, with six to eight overlapping scales.

Taxonomy

The species was first described by Carl Linnaeus in 1753. Over 30 synonyms are listed in Kew's Plants of the World Online database.

Distribution

Northern white cedar is native to an area in the southern part of eastern Canada and the adjacent part of the northern United States. It extends from southeastern Manitoba east throughout the Great Lakes region and into Ontario, Québec, New York, Vermont, New Hampshire, Maine, Prince Edward Island, New Brunswick, and Nova Scotia. Isolated populations occur in west-central Manitoba, and to the south in Massachusetts, Connecticut, Ohio, and Illinois and in the Appalachian Mountains of Kentucky, Tennessee, North Carolina, Pennsylvania, Maryland, Virginia, and West Virginia. In Canada, its range reaches the Arctic treeline and the southern tip of Hudson Bay.

Ecology

Northern white cedar grows naturally in wet forests, being particularly abundant in coniferous 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 white cedar 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 specimen is 34 m (112 ft) tall and 175 cm (69 in) diameter, on South Manitou Island within Leelanau County, Michigan.

Uses

Thuja occidentalis is commercially used for rustic fencing and posts, lumber, poles, shingles, and in the construction of log cabins. It is the preferred wood for the structural elements, such as ribs and planking, of birchbark canoes and the planking of wooden canoes.

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

Eastern white cedar – as arborvitae – is a popular ornamental plant used in both residential and commercial landscapes.

Cultivation

T. occidentalis is widely used as an ornamental tree, particularly for screens and hedges, in gardens, parks, and cemeteries. Over 300 cultivars exist, showing great variation in colour, shape, and size, with some of the more common ones being 'Degroot's Spire', 'Ellwangeriana', 'Hetz Wintergreen', 'Lutea', 'Rheingold', 'Smaragd' (or 'Emerald Green'), 'Techny', and 'Wareana'. It was introduced into Europe as early as 1540.

• These cultivars have gained the Royal Horticultural Society's Award of Garden Merit:
• 'Danica'
• 'Golden Tuffet'
• 'Holmstrup'
• 'Rheingold'
• 'Smaragd'