The leaves are needle-like, 7 to 25 mm (1⁄4 to 1 in) long and 1 to 1.5 mm (1⁄32 to 1⁄16 in) broad, soft, blunt-tipped, only slightly flattened in cross-section, pale glaucous blue-green above, and with two broad bands of bluish-white stomata below with only a narrow green midrib between the bands; they differ from those of any other species of hemlock in also having stomata on the upper surface, and are arranged spirally all around the shoot.

[4][5][6] There are three taxa, two subspecies and a minor variety:[4][6] The species name mertensiana refers to Karl Heinrich Mertens (1796–1830), a German botanist who collected the first specimens as a member of a Russian expedition in 1826–1829.

Arborescent individuals that have narrowly conical crowns until old age (300 to 400 years) and shrubby krummholz on cold, windy sites near timberline add beauty to mountain landscapes.

[8] Best development of mountain hemlock is on loose, coarse-textured, well-drained soils with adequate moisture, and in British Columbia, on thick and very acidic organic matter and decayed wood.

[8][10] Mountain hemlock will grow on most landforms, but individuals typically develop best in mixed stands of forest on sheltered slopes or in draws.

The preference for relatively moist, cool sites evidently becomes a necessity as the climate becomes more continental in western Montana and more mediterranean in the central Sierra Nevada at these extremes of its range.

[10] In these locations, mountain hemlock typically grows in isolated populations in north-facing glens and cirque basins where snow collects and may remain well into summer.

In many communities of the mountain hemlock forest in British Columbia and Washington and northern Oregon, Pacific silver fir is a major climax species.

Several cultivars have been selected, mainly for intensely glaucous foliage color including: This article incorporates public domain material from Joseph E. Means.