Because the people who named it were called Peter and Sapphire Tree ,so they named it after themselves
The only Shirley I know of in the plant world are Shirley Poppies.
There is a family of trees called Beech trees. Latin name is Fagus.
Because they are trees that you get in Christmas time so its called a Christmas tree instead of tree.
It is so that people can communicate and describe something.
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