The Umbral Rose is a flower added by Forbidden Magic. It spawns in a 5x5 area around a placed Umbral Rose Bush and can be crafted into Shadow Ink as a Squid-friendly ink alternative to create research notes.
There's no sight more pathetic than a soggy Thaumaturge. For all your great and miraculous powers, you still have to go jump in the nearest lake and hunt for squids every time you want to refill your inkwell.
You're done squid hunting. By infusing a rose with tenebrae and victus, you create a flower that spreads like a weed and whose petals can be crushed for ink.