what is it?

Several times now I have pulled a bit of this stuff out of my tank. I've found it in the vallisneria and watersprite. I thought at first it was some kind of hair algae, or bits of feeder roots that came to the surface and broke off? But this last, largest clump I found has a really symmetrical growth pattern, the segments are flat. I did a search on algae types and watersprite and didn't find anything similar. Asked on a planted tank forum- it's riccia fluitans, also called crystalwort. Something that I'd rather not have thrown away, now that I know what it is! I don't know if it would grow with the low light, no-C02 setup I have, but if it did, that would be a cool little plant. It's so primitive looking.

Seems that when people want it, they can't find it to buy. And when they have it by accident, they want to get rid of it! If I find it in my tank again, I'll at least leave it alone for a while and see what it does...