Tsuga mertensiana - mountain hemlock

Mountain hemlock is a tree of the upper slopes of the mountains of western North America, its range extending from Alaska to California. It grows in moist soils in forests, thin-peated spruce mires and rocky areas, favouring cool, moist, northern slopes. It is often considered the beauty of the genus. Unlike the other species, mountain hemlock’s concave needles are the same colour on both surfaces and spread in all directions. This gives the tree an attractive, fluffy, cedar-like appearance.

Tsuga heterophylla - western hemlock

Western hemlock, native to the western parts of North America, is the largest of the hemlocks. Capable of standing deep shade, it grows in mixed forest on mountain slopes and forms dense stands. The crown is narrowly conical and the branches almost horizontal, though the leader and tips of the branches droop in typical hemlock fashion. The needles vary in length, growing outwards and upwards from the branches, covering them so that with age they appear from a distance to be covered in mossy layers.

Tsuga diversifolia - northern Japanese hemlock

The hemlock (Tsuga) genus gets its scientific name from the Japanese word tsuga. The northern Japanese hemlock is one of the two hemlock species native to Japan, and its natural habitat is the mountains of Honshu Island between 900-2200 metres, approaching the tree line. On the best sites it reaches heights of 25 metres but higher up the slopes remains a low shrub. Compared with other hemlocks the crown is exceptionally dense and broad, reminiscent of broadleaf trees. On their undersides the needles are strongly silver-white, of varying length, broad and notched at the tip.

Tsuga caroliniana - Carolina hemlock

The Carolina hemlock is rare, only growing naturally in a restricted area of the Appalachian Mountains in the United States. Its natural habitat is rocky slopes and ravines at heights between 750-1200m asl, in the same areas as catawba rhododendron (Rhododendron catawbiense) and calico bush (Kalmia latifolia). Growing to heights up to 30 metres, the Carolina hemlock is smaller than the other North American species, resembling its close relative eastern hemlock in appearance.

Tsuga canadensis - eastern hemlock

Eastern hemlock grows over a large range in eastern North America. Like the other hemlocks, it is a so-called forest climax species, growing quite happily when young under a shading canopy. Clues to its adaptation to shade are the needles, which densely cover the branches. The species grows rather slowly but eventually becomes a large broad tree. On open sites it produces multiple branches and remains shrubby in habit.