Calocedrus, commonly known as incense cedar (or incense-cedar), is a small genus of coniferous trees in the cypress family Cupressaceae, placed in the order Cupressales. The genus was first formally described in 1873. It comprises four recognised extant species: three native to eastern Asia (China, Taiwan, and Vietnam) and one — Calocedrus decurrens, the California incense cedar — native to western North America.
Morphologically, Calocedrus is closely allied to Thuja and shares the same flat, scale-like foliage arranged in overlapping pairs. The key distinction lies in the arrangement of those pairs: in Calocedrus they occur in apparent whorls of four, formed by successive opposite decussate pairs that are unevenly spaced (one pair close, the next distant), whereas in Thuja the pairs are evenly spaced. The seed cones are also diagnostic — Calocedrus bears cones with only 2–3 pairs of moderately thin, erect scales, compared with the 4–6 pairs of very thin scales typical of Thuja.
Among the species, Calocedrus decurrens is by far the most widely known. In its natural habitat along the Sierra Nevada and Cascade ranges it grows as a broadly columnar to spreading tree, but in cooler maritime climates such as those of Britain, Washington state, and British Columbia it develops a strikingly narrow, pencil-like crown whose cause remains unexplained. It is also prized for its strong drought tolerance, making it useful in low-water landscape plantings. The Asian species — C. macrolepis, C. formosana, and C. rupestris — are rarely encountered in cultivation.
Etymology
The genus name Calocedrus derives from the Greek words kalos ("beautiful") and kedros ("cedar"), meaning "beautiful cedar."
Distribution
Three species of Calocedrus are native to eastern Asia (China, Taiwan, and Vietnam), while a fourth, Calocedrus decurrens, is native to western North America, ranging through the mountains of California and Oregon.
Cultivation
Calocedrus decurrens, the California incense cedar, is the most widely cultivated species. It is particularly popular in regions with cool summer climates, such as Britain, Washington state, and British Columbia, where it develops an unusually narrow columnar form not seen in wild-habitat trees. It is valued for its drought tolerance. The Asian species are rarely grown in cultivation.
