The thin woody cone scales number from 4-6 pairs and are persistent and overlapping, with an oblong shape, they are also basifixed.

The closest relatives of Thuja are Thujopsis dolabrata, distinct in its thicker foliage and stouter cones, and Tetraclinis articulata (Ancient Greek θυία or θύα, formerly classed in the genus and after which Thuja is named), distinct in its quadrangular foliage (not flattened) and cones with four thick, woody scales.

T. plicata has wide distribution in the Pacific Northwest from Northern California to Alaska, reaching East into Idaho and central British Columbia.

T. occidentalis has populations in the Northeastern United States, reaching north into Ontario and Quebec, with some distribution as far south as Tennessee.

T. koraiensis is native to both North and South Korea and has a small population in the Northern Chinese province of Jilin.

[18] The newly rediscovered species T. sutchuenensis has extremely limited distribution in the mountains of Chengkou county in southeastern China.

Current research suggests that Thuja originated in the Americas and migrated to East Asia via the Bering land bridge in the Miocene.

Fossil records show that Thuja was significantly more widely distributed during the late Cretaceous and early Tertiary than we see today.

[19] The oldest known Thuja fossil is of T. polaris (an extinct species) from the Paleocene of Ellesmere Island in present-day Nunavut, Canada.

[24] Its combination of light weight and resistance to decay has also led to T. plicata being widely used for the construction of bee hives.

[citation needed] Oil of Thuja contains the terpene thujone which has been studied for its GABA receptor antagonizing effects, with potentially lethal properties.

[27] The natives of Canada used the scaled leaves of Thuja occidentalis to make a tea that has been shown to contain 50 mg of vitamin C per 100 grams; this helped prevent and treat scurvy.