I have some fresh water seaweed (Subwassertang) that grows in any condition as long as no ferts are given to your plants. It is a very primitive/interesting plant. I find my smaller fish put into my tank to clear some moss off of a log will munch on this as well. If you tie it to a rock it will bush out in a very attractive manner.
I would suggest it to anyone who has a small tank, fry or other small fish that like to hide, or a low amount of light. With CO2 injection the plant will get bushier then without but it will grow no matter what.
You should check it out.