This was planted by a previous owner, and I long wondered what it was - apart from obviously being in the hibiscus family.
The flowers change from yellow to pink as they age, and attract large honeyeaters to feed at them, e.g. https://pbase.com/donfranklin/image/150742521 .
I eventually tracked it down and was amazed to discover that it is a species native to one small island off Norfolk Island in the Pacific Ocean.
And that in the wild there's just two clumps left in existence; https://en.wikipedia.org/wiki/Hibiscus_insularis .