There is a type of refugium algae that grows in freshwater. I ordered some from an online store and it is still growing well. Botanical name is Chaetomorpha. Slow growing, coarse and springy like a plastic loofah sponge.
I don't know if there is a point of a refugium in FW. I'm wondering what I have, because it hasn't melted, and it looks like chaeto. How long does it take to melt? I've had it in there for over a week now. (Darker spaghetti like plant behind the peacock java).
Riccia won't anchor/attach itself to anything, but can get caught on things. (like Subwassertang/Round "Pellia" won't anchor, though Pellia can).
Some consider Riccia as a pest. It can break into little strands and get dispersed around the tank, making it hard to really get rid of all of it (same as subwassertang).
Bit tricky to attach/tie riccia down to anything (it likes to float). Using netting works though.