American Arbor-vitae or White Cedar Thuja occidentalis L.
This tree is a native of the eastern United States and Canada, where it is found mainly in river valleys and moderately swampy sites. It was introduced into Europe as early as 1540 and today is widely cultivated there, especially in parks and cemeteries. The growth rate is slow and the tree attains a height of only 20 metres or so, with oblong crown reaching to the ground. The grey-brown furrowed bark peels in narrow, longitudinal strips. The terminal shoot stands erect, the lateral branchlets are more or less horizontal. The leaves are scale-like and grow in twin pairs closely pressed to each other. The upper-surface of the twig is dark green, the under-surfacc yellow green without markings. The inconspicuous flowers are borne at the tips of the branchlets. The oblong cones, 7 to 10 mm long, open in October to release the small, winged seeds.
The tree is very resistant to frost and tolerates both shade and pruning well. It is used to form all green hedges. In sunny situations it is affected by changes in temperature, and sometimes frost causes it to dry up. Its many ornamental forms make it particularly desirable for park landscaping.
Leaves: Scale-like, growing in pairs, the tips of lateral needles curved inward.
Flowers: Female greenish, 2 mm long; male grey-green.
Cones: 7—12 mm long with 3 to 5 pairs of scales.
Seed: Two winged