Minecraft wiki entry for Development_versions, associated text: Currently added as a feature code file, does not generate in the overworld yet, and can only be generated using add-ons.
Adaptive to the environment: every type of cave generation can be a lush cave.
Moss covers the floors and ceilings, along with moss carpets and grass on the floors.
Spore Blossoms grow from the ceiling and drip particles.
Contains clay pools where dripleaf plants grow out of them.
Clay pools will sometimes generate water sources over air, and the water is suspended and does not flow. This has yet to be fixed.
Contains azalea bushes (both variants).
Cave vines with glow berries grow from the ceiling and light up the caves.