There are four North American species. 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). This adelgid, related to aphids, was introduced accidentally from eastern Asia, where it is only a minor pest.
The Common North American Hemlocks
Leaves: persistent or deciduous, linear or needle-like.
Fruit: Woody cones.