Hemlock trees (Tsuga): how to identify them

Eastern hemlock

Eastern hemlock (Tsuga canadensis) is also called Canada hemlock and hemlock spruce, and in Québec pruche du Canada. The USDA Forest Service's Silvics of North America maps it from Nova Scotia, New Brunswick and extreme southern Quebec west through south-central Ontario and northern Michigan to the western third of Wisconsin, with outliers in northeastern Minnesota. In the United States it grows throughout New England, New York, Pennsylvania and the Middle Atlantic States, and south along the Appalachians into northern Georgia and Alabama.

It is a slow, long-lived tree. Typical old stands carry trees approaching 400 years, 35 to 40 inches across and over 100 feet (30 m) tall, and the record age is reported as 988 years (Silvics). NRCan calls it very shade-tolerant: small trees can wait in closed stands for decades. NRCan says it needs a cool, moist site and grows in pure stands or with yellow birch, eastern white pine, red spruce, sugar maple and American beech (NRCan).

The closely related Carolina hemlock (Tsuga caroliniana) is limited to Appalachian slopes from Virginia and West Virginia into Georgia, inside eastern hemlock's range (Silvics). If you are in those mountains, a single sprig may not separate the two.

Western and mountain hemlock

Western hemlock (Tsuga heterophylla), also called Pacific hemlock, is a much bigger tree. The Forest Service's western hemlock silvics gives heights of 165 to 200 feet (50 to 61 m) as not uncommon on good sites, a maximum of 259 feet (79 m), and a recorded age of over 700 years. It grows along the Coast Ranges from central California north to the Kenai Peninsula in Alaska, on the Cascades in Oregon and Washington, and inland on the west side of the Continental Divide in Idaho and Montana, north to Prince George, British Columbia.

Virginia Tech's western hemlock fact sheet gives flat needles 1/4 to 3/4 inch with two white bands beneath, and egg-shaped reddish-brown cones about 1 inch long; the Forest Service gives 0.75 to 1.25 inches. On the Pacific Coast it grows beside Douglas-fir, western redcedar and Sitka spruce; the Pacific Northwest tree guide sorts them zone by zone. Western redcedar carries tiny scale-like leaves instead of flat needles; the cedar page covers it with the other trees called cedar.

Higher up, mountain hemlock (Tsuga mertensiana) looks different. NRCan's mountain hemlock factsheet describes blunt needles 20 to 30 mm long, rounded in cross-section and bluish-green on both sides, crowded around the twig, and cylindrical cones 30 to 80 mm long. It grows in subalpine forests at 750 to 1,800 m (about 2,500 to 5,900 ft) and becomes a low, spreading shrub on exposed ridges.

Hemlock tree vs poison hemlock

"Hemlock" is two unrelated plants, and the confusion matters because one of them is dangerous.

• Hemlock tree (Tsuga): an evergreen conifer in the pine family, with needles and woody cones. NRCan and the Forest Service file it with the other conifers.
• Poison hemlock (Conium maculatum): a weed, not a tree. Penn State Extension's poison hemlock page describes a biennial that forms a low rosette of leaves in its first year and a stem up to 6 feet tall in its second, with very distinctive purple spots on the stem and small white flowers in umbrella-like clusters from June into August. It states that all parts of poison hemlock are toxic to humans and other animals.

If the plant has needles and cones, it is not poison hemlock. If it is a soft-stemmed plant with purple-spotted stems and white umbrella-like flower clusters, keep away from it and do not handle it to identify it. Never eat any part of either plant on the strength of a web page or an app; for a plant a child or pet has swallowed, call a poison center.

Hemlock vs yew, fir and spruce

Short flat needles in two rows also belong to yews and firs, so check the underside and the fruit. NC State Extension's English yew profile describes needles dark green above and yellowish-green beneath, and a red, fleshy, cup-shaped aril around the seed instead of a cone; it also rates the yew as highly poisonous. Hemlock needles have two white lines beneath, and the tree bears small brown cones. The yew page covers the yews in detail.

Douglas-fir, the hemlock's neighbor in western forests, has longer needles, 3/4 to 1 1/4 inches, and cones 3 to 4 inches long; the Douglas-fir page shows its three-pointed cone bracts. Spruces have four-sided needles on woody pegs, and the spruce page sorts the species.

In Tree Identifier, a photo of the underside of a sprig with a cone attached gives the most to work with. Eastern hemlock is among the 138 species in the app's Collection. The app shows no confidence score and no look-alike list, so check a hemlock answer against the white lines and the cone size above, and use the follow-up chat to ask how it differs from the yew or fir next to it.