Can anyone tell me what this is? I received it from a friend a few years ago and while I haven't killed it, I feel like it should be growing more than it has. Pieces fall off here and there and sometimes I just stick 'em back in the soil and eventually they root and grow into new stalks.

I'd like more info so I can treat it better but I can't figure out what it's called! It's in a sunny window and I try to water it when it's almost dried out. I should maybe repot it by now, in the 5-1-1?

Thanks in advance! : )

Nicole