Black Hemlock or Tsuga

The hemlock of this entry is the conifer, not the poisonous herb Conium maculatum. Unlike that herb, Tsuga species are not poisonous. The herb is unrelated to the coniferous trees of the genus Tsuga. Tsuga is the Japanese name for hemlock.

The tree ranges from northeastern Minnesota eastward through southern Quebec and into Nova Scotia. It is found mostly in cool coves but can also be present on rock outcrops, especially on north-facing slopes. The tree can grow to heights of more than 30 metres and tolerates shade, moist soil and slopes. The oldest recorded specimen, found in Tionesta, Pennsylvania, was at least 554 years old. The needles are flat and green above, with shallow white bands on the underside. Hemlocks have shallow root systems that leave them susceptible to drought, wildland fire and wind fall. The dense, flat needles help regulate stream temperatures. The understory of hemlock forests is characterized as dark, damp and cool.

Hemlock wood is used in construction and for railroad ties. Eastern hemlocks are popular as ornamental trees. Eastern hemlock is the state tree of Pennsylvania.

The invasive hemlock woolly adelgid infests and eventually kills the trees. Declines caused by the adelgid have led to the species being listed as Near Threatened on the IUCN Red List. The adelgid is an insect native to East Asia that feeds by sucking sap from hemlock and spruce trees.

The ester content of spruce and hemlock oils, calculated as bornyl acetate, is 37-45%. Bornyl acetate has the molecular formula C₁₂H₂₀O₂ and a molecular weight of 196.29. One volume of the oil dissolves in at least one volume of 90% ethanol, and solutions may become hazy when more than two volumes of 90% ethanol are added.

Regulatory identifiers

Hemlock oil is registered under CAS number 8008-10-4 and carries the FEMA number 3034. It also appears in the list of substances added to food, under the entry for hemlock needles and twigs, oil (Tsuga spp.).