Answer: Thuja "Smaragd" (a synonym for "Emerald") is a Thuja occidentalis cultivar originally from Denmark. It should hold a good green color in winter and reach 10 to 15 feet tall and 3 to 4 feet wide.
Thuja "Green Giant" was introduced by the US National Arboretum about ten years ago. It is a larger plant and grows about twice as wide. Here is information and photos of it.
Unfortunately, I am not sure which plant this one would be if it has two different labels on it. I'm sorry I can't be more helpful.
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