with newts not needing much light in their set ups,planting in an aquatic or semi aquatic set up can be a problem. however there are some almost indestructable aquatic plants that do well in low light situations. The main one I use are Anubias, java moss java fern, and willow moss, all of these do well, and can be used to good effect in newt set ups. for a low light terrestrial set up, devils ivy or normal ivy work well.
Myriophyllum, or Elodea densa should be ok. They are both fairly common in ponds, however getting hold of Myriophyllum* can be hard sometimes, as I believe it's a banned plant species in the UK.