It's a toadstool leather. Not a leather mushroom. ;)
It looks very bleached (white). What kind of light do you have? Usually they are very hardy and can recover from damage or injury. I wouldn't remove it unless it starts melting away and disintegrating.
How long has the leather been in your tank?
And have you made any changes to the tank in the past few weeks?
What about the smaller leathers next to it, are they retracted for long periods too?