Some advise

Is it possible to grow any kind of live plants in a normal freshwater tank, nothing that needs to be rooted, but omething more like moss, or the "duck weed" i was reading about, i have a 30 gal tank, with small black gravel on bottom, half is pretty heavily planted(fake), with a cave, the other side more open with only a few hunks of drift wood on the bottom, not sure if this is real wood, since its mounted to a plastic block, but i was just wondering if there some kind of carpet moss that doesnt need massive lights. Something that could just live off of fish waste, help keep ammonia down and just hang out on my drift wood, alos i was reading about the duck weed and it sounds very interesting, i have more of a tall 30 gal tank, so i think the filter shoul not get clogged to back, im sure a sponge could be capped at the end, also could prolly extend the intake tube a bit lower down, since the duck weed is mainly on top, im not ready to do this yet, my tank is still cycling, this a few month in the futrure, once my tank get established, and i figure this hobby out a bit, but i want some advise and some reaserch in advance, let me know what you guys think, if there is any moss like live plant or some input about this duckweed, are these thing i can just toss in? Thanks in advance!! [withstupid]