Arborvitae, thuya, cèdre [Greek name for some evergreen, resinous trees]

Kenton L. Chambers

Trees evergreen, small to large. Branchlets flattened, in fan-shaped, flattened, frondlike sprays. Leaves opposite in 4 ranks. Adult leaves heteromorphic; those on larger branchlets with sharp, erect, free apices to ca. 2 mm; those on flattened lateral branchlets crowded, appressed, scalelike, lateral pairs keeled, facial pairs flat; abaxial glands present or absent. Pollen cones with 2--6 pairs of sporophylls, each sporophyll with 2--4 pollen sacs. Seed cones maturing and opening first year, ellipsoid, (6--)9--14(--18) mm; scales persistent, 4--6 pairs, overlapping, oblong and basifixed, thin and woody, 2--3 central pairs fertile, uniformly thin or with slightly enlarged apex, remaining scales sterile. Seeds 1--3 per scale, lenticular, equally 2-winged; cotyledons 2. x = 11.

Species 5 (2 in the flora): North America, e Asia.

Two Asiatic species, Thuja koraiensis Nakai (Korean arborvitae) and T . standishii (Gordon) Carrière (Japanese arborvitae), are occasional in cultivation. They differ from the native species in having more closely spaced long-shoot leaves with shorter, spreading points.

Lower Taxa

• Thuja occidentalis Linnaeus
• Thuja plicata Donn ex D. Don