Happened to be in Auckland Botanic Gardens earlier this week and guess what I found? Both of our native hibiscus in flower (see the post below for information about a plant now not considered to be a native hibiscus).
Read more about Hibiscus richardsonii here, although I am surprised to see it growing so tall in the photos. The plants in Auckland were much smaller, more a ground-cover type of thing.
Hibiscus diversifolius is more of a shrub that grows about 1-2m high. It has fine, sharp bristles on its stems and leaves.
Interesting to note that it is also found in other parts of the Southern Hemisphere.