Citrumelo

Citrumelo (× Citroncirus spp.) 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.), developed by Walter Tennyson Swingle.

Citrumelo
Hybrid parentage	Poncirus trifoliata (Japanese bitter orange) x Citrus × paradisi (grapefruit)

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]

The fruit are yellow, and up to 4 inches across in size.^[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]

Taxonomy

See also: Citrus taxonomy § Trifoliate orange

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.