In which year did Canada adopt the maple leaf as its flag?

Fun fact: the leaf on the flag is not supposed to represent a specific species, just maple trees in general. There's a popular factoid about how it's supposed to be a sugar maple but is actually an invasive Norway maple, but that is incorrect. It's a stylized leaf resembling many species.

While there is a maple leaf on Canada's flag, it is not true that the flag of Canada is a maple leaf.