[cypher]

It looks like moss to me but I'm not sure, you do have to be careful with anything growing in a ham set up as you can't really monitor how much of it they might eat & unless you have a completely open top tank like that condensation, humidity & mould can be a problem. The other thing is for anything green to grow well & continue to grow it will need lots of light which hamsters don't so it's not an easy long term set up to do or manage.