I have a live plant in my fish's 1.5 gallon tank and one of the leaves turned brown ?

Question

and its leaving stuff on the side of the tank and on the mirror... What is it and is it safe for my beta fish?

Answer 1

Just remove the leaf. It's not a big deal.

Answer 2

No, it is not safe.  The live plant is rotting.  

Answer 3

It is probably not getting enough light for photosynthesis, but it is perfectly natural for leaves to turn brown. It turns brown from the food trapped in it, or it is like a waste storage for the excess sugar or glucose.