is also called Swingle citrumelo trifoliate hybrid, because it is cold hardy and is a hybrid between a 'Duncan' grapefruit and a trifoliate orange (Poncirus trifoliata (L.) Raf.
Citrumelo is widely employed as a citrus rootstock,[1] being resistant to the severe citrus tristeza virus and to phytophthora root rot as well as to blight, cold, and citrus nematode.
[2] The trees can survive temperatures into the teens (Fahrenheit);[3] one specimen in North Carolina reportedly survived temperatures below zero Fahrenheit.
[4][3] Their taste is described as "like a cross between a lemon and a grapefruit",[3] or "if sprinkled with sugar [then] like an ordinary grapefruit, harvested perhaps a bit too early".
[4] Trifoliate orange, according to Swingle, belongs to a citrus-related genus called Poncirus, while grapefruit equivocally belongs to the genus citrus, hence the botanical name × citroncirus is a hybrid genus, derived from citrus and poncirus.