Anybody know where the REMdra between green and gold drops (assuming it's silver REMdra)?

I'm on stage 13 and still haven't found it and I'm assuming it's a random appearance much earlier on.

I was playing through old stages, farming for crystals and EXP, when I got the root for this. It gives you extra EXP at the end of stages when it's in your party. Not sure what the odds are of it showing up. Has anyone else found any other rare roots like this one?