On another site, someone posted the same question. They said the leaves were turning black and something about being crossed with purple urkle and when people read that, they said, "clone it." It was noted as being black, not purple. Anyway, I've never seen black on a leaf before, but if the room has kind of high humidity, usually due to a lack of fresh airflow, then this most likely is a fungus or mold. A shame as it looks like a nice plant otherwise. Don't consume anything when you don't know what it is.