Yes it's Marchantia! I actually did some studies of the sperm cells of that plant (they make motile sperm instead of pollen) when I was working on microtubule disrupter herbicides with the USDA.
From my experience you definitely want to get rid of it before it takes the place. it is a scourge to nursery people that use lots of pots.
Kevin
PS MERRY XMAS ALL!
