Tsuga is the genus that contains all true hemlock species. It is so-named because of the similarity of the scent of the foliage to the completely unrelated poison hemlock (Conium maculatum)—the same stuff that killed Socrates. Tsuga foliage however, despite a few reports of causing mild skin irritation, is not poisonous.
Hemlock tends to have poor decay resistance. Some species are mixed with fir species (Abies genus) and used in construction under the label “HEM/FIR.”
Eastern Hemlock (Tsuga canadensis)
Carolina Hemlock Tsuga caroliniana
Western Hemlock Tsuga heterophylla
Mountain Hemlock Tsuga mertensiana