Original: Tilia is a genus of about 30 species of trees, native throughout most of the temperate Northern Hemisphere, in Asia (where the greatest species diversity is found), Europe and eastern North America; it is not native to western North America.
Simplified: Tilia is a genus of between 30 and 45 species of trees in the Northern Hemisphere, in Asia (where the greatest species diversity is found), Europe and eastern North America; it is absent from western North America.