there are a few marine plants that i think could be kept in a nano reef. shaving brush, mermaid fan and halamida are a few that seem to do well. the trick is 1-keep herbavore fish(tangs, rabbits etc.) away, 2- bright light, 3- deep sand bed(2" -3" as they spread by underground rhizomes) and 4- enough nutrients for thier growth. the last is the trickiest to manage because too much nutrients and you get trouble algae but too little and your marine macros starve. i have also had luck with feather caulerpa and grape caulerpa but keep on top of it, it can go crazy. good luck.