Looks like a lichen. Nothing disgusting about it really, they are very interesting plants.

Thanks Steragram

It's a liverwort, one of the most primitive land plants. There's no harm to it, as long as it isn't smothering out young seedlings.

Thanks Tugbrethil - it will be getting removed tomorrow!

Why? Nothing to harm your precious plants!

I rather like them, been on the planet in one form or another for millions of years. Fossilized ones pre date ferns in fact. I leave it alone. You do get it on waterlogged plants as you have found out. They dont have a proper root system so need to be in moist conditions.

i think its rather nice myself .

It looks like a group of green pop eyed little people looking at you from the pot. Think how reproachful those eyes will be when you come along to dispose of them.

from my twisted perspective it looks a bit like coral but green instead of white .

I just think it looks great...

I like it too, even though I got its name wrong.Its still a very interesting plant though, and has a fascinating sex life!

lucky plant lol .

very interesting sex life. it has male swimming gametes like animals. no pollen for this little thing.
i too think they are great.