<unk>  (Poncirus<unk> , synonym Citrus<unk> , is a member of the family Rutaceae, closely related to Citrus, and sometimes included in that genus, being sufficiently closely related to allow it to be used as a rootstock for Citrus and to readily hybridize with all Citrus species.
It differs from Citrus in having deciduous, compound leaves, and pubescent (downy) fruit.
It is native to northern China and Korea, and is also known as the Chinese Bitter<unk>  or Hardy<unk> .
The plant is a fairly cold-hardy citrus (USDA zone 6) and will tolerate moderate frost and snow, making a large shrub or small tree 4–8 m tall. Because of the relative hardiness of Poncirus, citrus grafted onto it are usually hardier than when grown on their own roots.
Trifoliate orange
Trypan Blue
Carbon black
Phenol red
Polynoxylin
Hermaphrodite
SeHCAT
Nessler's reagent