Bone meal can be used on saplings that are on moss blocks, but they cannot grow into trees.
Saplings dont grow on top of moss blocks
Azalea and Flowering Azaleas can take bone meal despite being on clay
Bone meal is consumed when used on fern, grass and seagrass even if it cannot grow
You can use bone meal on sea pickles in situations where no sea pickles will grow
Single dark oak saplings accept bone meal despite not being able to grow
Red and brown mushrooms accept bone meal even on blocks not in #minecraft:mushroom_grow_block
Bone Meal can still be used on a Glow Lichen when it is unable to grow