What is the difference between the words "spruce" and "fir" (or even "fir tree")?
Could they be used interchangeably, for example, when referring to a kind of evergreen trees people decorate on Christmas and New Year holidays?
EDIT (more details about the roots of question):
I've had a conversation with my North American friend about species of trees that are symbols of the holidays in different cultures and was confused about discovering that in some dictionaries both "spruce" and "fir" could be translated similarly into Russian.
Thanks to @TimRomano and @deadrat, I see now that those are clearly distinguished species from the botany point of view. Therefore, let me narrow the question down a little.
When you want to say "Christmas tree", but more specifically in terms of a kind of the tree, could you say, for instance:
Christmas fir (spruce) is the symbol of Christmas in this country.
Or it sounds unnatural as the phrase and better to say something like:
They use fir trees as Christmas trees in their country.