This is not exactly a plant but I have no idea what it is. It is growing (or existing) in a sand school that has grass growing in it now. It is little bubbly stuff and is very slippy.
Nostoc. It likes wet ground, and is harmless.
Thank you. Any idea on how to get rid of it as it is in a sand school (horse arena) and the horses are slipping on it.
Apparently baking soda is effective: