The most critical way to differentiate between Eastern and Western Hemlock, despite their similar foliage, is by observing the arrangement of leaves on their branches.
Key Distinguishing Feature
While both Eastern Hemlock (Tsuga canadensis) and Western Hemlock (Tsuga heterophylla) share a similar yew-like appearance with their short, flat needles featuring two white lines beneath, a key difference lies in the way their leaves are presented along the branch.
Eastern Hemlock is uniquely identified by a distinctive line of reversed leaves running along the top of its branches. This arrangement means that the white undersides of these particular leaves are prominently visible, facing upwards.
In contrast, the foliage of the Western Hemlock typically lies flatter along the stem, lacking this characteristic line of inverted leaves. All leaves on Western Hemlock branches generally present their green upper surfaces, with the white undersides only visible when the needle is turned over.
Visual Cues for Identification
When examining a hemlock branch, pay close attention to the following:
- Eastern Hemlock: Look for a noticeable strip of leaves on the upper side of the branch where the lighter, white undersides of the needles are clearly facing upwards. This creates a subtle, light-colored stripe along the top.
- Western Hemlock: The leaves on Western Hemlock branches will generally lie in a flatter, more uniform spray, with the green upper surfaces of all needles predominantly visible. There will be no obvious line of reversed, white-underside-up leaves along the top.
Comparative Summary
To easily distinguish between these two hemlock species, consider the following visual characteristics:
| Feature | Eastern Hemlock (Tsuga canadensis) | Western Hemlock (Tsuga heterophylla) |
|---|---|---|
| Foliage Aspect | Needles are yew-like with two white lines underneath. Crucially, a line of reversed leaves along the top of the branch shows their white undersides uppermost. | Needles are yew-like with two white lines underneath. Foliage lies flatter along the branch, lacking the distinct line of reversed leaves on the upper side. |
| Key Identifier | Presence of a prominent line of upward-facing white leaf undersides on the branch top. | Absence of upward-facing white leaf undersides on the branch top; leaves generally lie flat. |
By focusing on this specific arrangement of leaves, particularly the presence or absence of the reversed leaves on the upper surface of the branch, you can reliably tell the difference between Eastern and Western Hemlock.
