To what taxonomic subfamily of flowering perennial evergreen plants do the tallest grasses in the world belong?

Bambusoideae

Bambusoideae is a diverse subfamily of grasses that includes over 1,400 species, ranging from tiny groundcovers to giant timber stalks. Some species are famous for their incredible growth rates, capable of growing up to 35 inches in a single 24-hour period. Because they are technically grasses rather than trees, they lack a vascular cambium and do not produce annual growth rings.