mountain hemlock vs black hemlock

mountain hemlock and black hemlock both are nouns.

Word	Noun	Adjective	Verb	Adverb
mountain hemlock	Yes	No	No	No
black hemlock	Yes	No	No	No

As nouns, mountain hemlock and black hemlock are synonyms defined as:

mountain hemlock and black hemlock: large evergreen of western United States; wood much harder than Canadian hemlock

Other synonyms of mountain hemlock include Tsuga mertensiana.

mountain hemlock (noun)	black hemlock (noun)
large evergreen of western United States; wood much harder than Canadian hemlock	large evergreen of western United States; wood much harder than Canadian hemlock