Suaeda novae-zelandiae is, as the name implies endemic. What is interesting is that is is a scarce species in northern New Zealand, and that it becomes more common as one heads south of Auckland. Puzzled as to why I once asked Dr Trevor Partridge (formerly DSIR Ecology Division), and he explained that is an extreme halophyte, so it does best in very salty conditions. in northern New Zealand estuaries tend to contain more clay, which traps salt so stopping it being available to plants, thus in those sites Suaeda competes poorly. Further south less clay, more salt, more Suaeda. This seems to make sense.