Thuja occidentalis is an evergreen coniferous tree, in the cypress family Cupressaceae, which is native to the northeast of the United States and the southeast of Canada, but widely cultivated as an ornamental plant. T. occidentalis has fan-like branches and scaly leaves. Thuja occidentalis 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 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 foliage of Thuja occidentalis is rich in Vitamin C but due to the presence of the neurotoxic compound thujone, internal use can be harmful if used for prolonged periods or while pregnant.

The essential oil within the plant has been used for cleansers, disinfectants, hair preparations, insecticides, liniment, room sprays, and soft soaps. In the 19th century, Thuja was in common use as an externally applied tincture or ointment for the treatment of warts, ringworm and thrush. An injection of the tincture into venereal warts is said to cause them to disappear. 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.