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.