[6][7][8][2][9] They are medium-sized to large evergreen trees, ranging from 10–60 metres (33–197 feet) tall, with a conical to irregular crown, the latter occurring especially in some of the Asian species.

The leaves are flattened to slightly angular and range from 5–35 millimetres (3⁄16–1+3⁄8 inches) long and 1–3 mm (1⁄32–1⁄8 in) broad.

The leaves are less flattened and arranged all round the shoot, and have stomata above as well as below, giving the foliage a glaucous colour; and the cones are the longest in the genus, 35–80 mm (1+3⁄8–3+1⁄8 in) long and cylindrical rather than ovoid.

[6] The oldest fossils attributed to the genus are twigs, known from the Early Cretaceous of Inner Mongolia, China, though their relationship to modern Tsuga is not unambiguous.

The earliest pollen attributed to the genus is known from the Upper Cretaceous of Poland, dating to around 90 million years ago.

Abundant remains are only known from Eocene onwards, when the modern Tsuga crown group is thought to have begun to diversify.

[11][12] While formerly present in the region Tsuga became extinct in Europe during the Middle Pleistocene epoch around 780-440,000 years ago, due to unfavourable climate change caused by the ongoing Quaternary glaciation.

[6] Moved to other genera: The species are all adapted to (and are confined to) relatively moist, cool temperate areas with high rainfall, cool summers, and little or no water stress; they are also adapted to cope with heavy to very heavy winter snowfall and tolerate ice storms better than most other trees.

[24] The two eastern North American species, T. canadensis and T. caroliniana, are under serious threat by the sap-sucking insect Adelges tsugae (hemlock woolly adelgid).

[26] Larger infected hemlocks have large, relatively high root systems that can bring other trees down if one falls.

The foliage of young trees is often browsed by deer, and the seeds are eaten by finches and small rodents.