Kumquat
They are much hardier than citrus plants as oranges. The 'Nagami' kumquat needs a hot summer, ranging from 25 °C(77 °F) to 38 °C(100.4 °F), but can withstand frost down to about -10 °C(14 °F). It grows in the tea regions of China where the climate is too cold for other citrus fruits, even the Mikan (also known as the Satsuma) orange.