Trees to more than 20 m tall; trunk to 1 m (or more) d.b.h.; bark reddish brown to light grayish brown, thin, flaking in long strips; crown ovoid-pyramidal when young, broadly rounded or irregular when old. Leaves 1-3 mm, apex bluntly pointed; facial leaves rhomboid, with a conspicuous, linear, glandular groove at center abaxially; lateral leaves overlapping facial
ones, boat-shaped, ridged, apex slightly incurved. Pollen cones yellowish green, ovoid, 2-3 mm. Seed cones when immature bluish green, subglobose, ca. 3 mm in diam., when ripe reddish brown, subovoid, 1.5-2(-2.5) × 1-1.8 cm; proximal 2 fertile cone scales 2-seeded, distal 2 fertile scales 1-seeded. Seeds grayish brown or purplish brown, ovoid or subellipsoid, 5-7 × 3-4 mm, slightly ridged. Pollination Mar-Apr, seed maturity Oct.
Platycladus is a distinct genus of evergreenconiferoustree in the cypress family Cupressaceae, containing only one species, Platycladus orientalis, also known as Chinese arborvitae, biota or oriental thuja. It is endemic to northwestern China. It is also now naturalised as an introduced species elsewhere in Asia: eastward to Korea and Japan; southward to northern India; and westward to northern Iran.
Although generally accepted as the only member of its genus, it has been suggested that the closely related species Microbiota decussata could be included in Platycladus, but this is not widely followed. Other fairly close relatives are Juniperus and Cupressus, both of these genera being graft-compatible with Platycladus. In older texts, Platycladus was often included in Thuja, which is reflected in one of its common names, "oriental thuja". But it is only distantly related to the genus Thuja. Differences include its distinct cones, wingless seeds, and its almost scentless foliage.
The binomial Platycladus means "with broad or flattened shoots". The qualifier orientalis refers to its native habitat in China.
The common name 'arborvitae' is from Latin, 'tree of life', and is based on its association with long life and vitality in Buddhist thought in China. This is probably based on the tree's unchanging evergreen nature in the cold dry climate of northwest China, and its longevity; some of the larger specimens planted around Buddhist temples in China are said to be in excess of 1,000 years old. It is called ce bai (側柏) in Chinese.
It is a small, slow-growing tree, to 15-20 m tall and 0.5 m trunk diameter (exceptionally to 30 m tall and 2 m diameter in very old trees). The foliage forms in flat sprays with scale-like leaves 2-4 mm long. The cones are 15-25 mm long, green ripening brown in about eight months from pollination, and have 6-12 thick scales arranged in opposite pairs. The seeds are 4-6 mm long, with no wing.
Platycladus orientalis is most probably a species of the transitional open woodland zone between the steppes of Inner Mongolia and the deciduous oak, oak-birch, and oak-pine forests of NE China. Even within its natural range it is now almost invariably found in secondary vegetation or, nearest to its original habitat, in more or less degraded woodland and forest. As a pioneer species which is relatively long-lived, it can dominate certain slopes for a long time if further disturbances remain absent. Elsewhere it grows together with Pinus tabuliformis, less frequently with P. armandii and Juniperus rigida; Betula chinensis and Populus tremula are followed in the succession by Quercus spp. (some of which may be evergreen) and Castanea. The most arid and steepest slopes may only be covered with Pinus tabuliformis and Platycladus, accompanied by Juniperus rigida and other shrubs, and this vegetation may not represent a seral type, but an edaphically determined climax. The climate in NE China is above all characterized by very cold winters. As a pioneer of relatively dry, open vegetation on often unstable slopes, P. orientalis has found abundant opportunity over much of China, and even beyond (e.g. NE Iran), to establish itself and spread after introduction. It is much used in afforestation in NE and Central China and commonly planted in Central Asia. Buddhism has been instrumental in its spread especially in the SW of China, where it can be abundant on steep slopes of river valleys, but is usually never very far from settlements, monasteries or temples