The original Serissa foetida is a native of southern China (zone 9 I believe).
However, according to IPNI, Lamarque listed it from Japan. Most of the fancy
cultivars were developed in Japan.
The bottom line is that Serissa is what our gardeners would call half-hardy. It
does not like severe prolonged heat, and benefits from a cool winter rest. On
the other hand it should not be left outdoors in Northern winters.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)