There are only a few plants that can do well in low-end brackish conditions. Java ferns, anubias and vallisnerias to name a few usually are fine in it. What is the salinity of the tank?
I've also read in places that dwarf sag does well... which set me down a path of growing dwarf sag... which seems to really grow well. also, not neccessarily aquarium plants, but check out mangroves and lemon bacopa.