Trees to 15(--38) m, stunted or prostrate in harsh environments; trunk to 0.9(--1.8) m diam., sometimes divided into 2--3 secondary stems, often reproducing by layering or forming erect, rooted branches from fallen trunks; crown conical. Bark reddish brown or grayish brown, 6--9 mm thick, fibrous, fissured. Leaves of branchlets (1.5--)3--5 mm, acute, dull yellowish green on both surfaces of branchlets. Pollen cones 1--2 mm, reddish. Seed cones ellipsoid, (6--)9--14 mm, brown; fertile scales usually 2 pairs, each minutely mucronate. Seeds ca. 8 per cone, 4--7 mm (including wings), reddish brown. 2 n = 22.

On mostly calcareous substrates, neutral to basic swamps, shores of lakes and rivers, uplands, cliffs, and talus; 0--900 m; Man., N.B., N.S., Ont., P.E.I., Que.; Conn., Ill., Ind., Ky., Maine, Md., Mass., Mich., Minn., N.H., N.Y., N.C., Ohio, Pa., Tenn., Vt., Va., W.Va., Wis.

Isolated stands of Thuja occidentalis occur north and east of its general range in Canada (to 51° 31' N latitude in Ontario, 50° N in Quebec). In the United States south of the Great Lakes and in southern New England, it occurs locally in scattered stands and is rare or extirpated at numerous former sites. In some areas, heavy winter browsing by deer greatly reduces reproductive success through elimination of seedlings or saplings.

Thuja occidentalis is widely utilized in ornamental silviculture and has more than 120 named cultivars. It was probably the first North American tree introduced into Europe (ca. 1566). It is an important timber tree; the wood is used for applications requiring decay resistance.

Tree 15 - 20 m tall, trunk 0.5 - 1 m in diameter

Leaves: scale-like, apressed, bright green above, paler beneath, 2 - 4 mm long, egg-shaped to rounded, dotted with a gland on back. Foliage turns yellowish to brownish green in winter.

Bark: grayish brown to reddish brown, fissured with shredding ridges.

Twigs: flattened into fan-like sprays, yellowish green, becoming reddish brown with age, soft textured, usually divided three to four times.

Buds: tiny, covered by the leaves.

Form: conical to broad pyramidal with horizontal branches to the ground.

Pollen cones: 1 - 2 mm long, egg-shaped to rounded.

Seed cones: 0.7 - 1.2 cm long, egg-shaped, with four to six pairs of scales but often only middle two pairs fertile. Ripened cones change from green to reddish brown, developing two seeds in each fertile scale. Seeds narrow-oblong, 2 - 3 mm long, with two wings nearly circling each seed. Pollination occurs from April to May.

Similar species: Thuja occidentalis is easily distinguished from the junipers found in the Chicago Region. It has flattened branches, all scale-like leaves, and woody cones. The junipers of the region all have berry-like cones and branches that are not flattened.

Habitat and ecology: Calcareous slopes with springs, bogs, and lightly shaded sandy slopes.

Occurence in the Chicago region: native

Notes: Resistant to decay, the wood of this species is used to make boats and canoes, posts for fences and boat docks, and shingles. It is also a commonly used landscape plant with many available cultivars. Native Americans taught French settlers to use the plant as a scurvy treatment. Therefore, the settlers named the tree arborvitae, French for "tree of life," which is still used as a common name.

Etymology: Thuja is the Greek name for the plant. Occidentalis comes from the Latin word for western.

Author: The Morton Arboretum

There are three old reports for this species from Lake County and I have an Umbach specimen collected near Pine. I collected it about 2 miles east of Indiana Harbor in 1906 but I have not seen it since in this county. No doubt later reports are based upon the early reports. Several authors report it from Mineral Springs bog, Porter County and Lyon reports a few trees near Tamarack. I have seen it in only two places in Porter County and, doubtless, there are only two colonies of it in the county. In the Mineral Springs bog there are quite a number of trees 4-6 inches in diameter but their number is rapidly decreasing. Buried remains of this species have been found as far south as Henry County.

Conical tree to 20 m, with widely spreading branches; ultimate branchlets very soft and flat, 1-2 mm wide; lvs closely imbricate, broadly ovate to rotund, 2-4 mm, glandular, persisting and enlarging on the older branches; cone ca 1 cm, the outer scales nearly as long as the inner; 2n=22. Moist or wet soil, often in swamps; Que. and N.S. to Hudson Bay, s. to N.J., O., n. Ind. and Ill., Wis., Minn., and in the mts. to N.C. and Tenn.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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