Maple trees are not classified into "kingdoms". Here's the breakdown of the scientific classification of maple trees:

* Domain: Eukarya (organisms with cells that have a nucleus)

* Kingdom: Plantae (plants)

* Phylum: Magnoliophyta (flowering plants)

* Class: Magnoliopsida (dicotyledons)

* Order: Sapindales

* Family: Sapindaceae

* Genus: Acer

* Species: Various, such as Acer saccharum (sugar maple), Acer rubrum (red maple), Acer platanoides (Norway maple), etc.

"Kingdom" is a high-level taxonomic rank. Maple trees, like all other plants, belong to the Kingdom Plantae. The term "kingdom" is not used to further classify organisms within a specific plant family like Acer (maple).