I can’t find the name of them but in one of the Star Wars novels the Millenium Falcon ends up trapped in some ice caverns and they encounter sentient clouds of gas, methane iirc.

So we do have some people making up cool aliens.

Oh, the Pequeninos in Speaker for the Dead. They were sentient humanoid beings that became the trees of their world when they died. There’s more to it than that, but that’s the gist.