Citrofortunella according to the Swingle system, is a hybrid genus, containing intergenetic hybrids between members of the genus citrus and the closely related Fortunella. As Citrofortunella is a merged word between Citro meaning Citrus, and Fortunella. Such hybrid often combine the cold hardiness of the Fortunella, such as the Kumquat, with some edibility properties of the citrus species. Citrofortunellas, which are all hybrids, are marked with the "X" before the word "Citrofortunella", for example × Citrofortunella microcarpa or × Citrofortunella mitis which refer to the same plant.
These plants are hardier and more compact than most citrus plants, often referred to as cold hardy citrus. They produce small acidic fruit and make good ornamental plants. Citrofortunella hybrids include:
Citrocirus also according to the Swingle system, is a hybrid genus, containing intragenetic hybrids between members of the genus citrus and the closely related Poncirus, which includes the trifoliate orange, a cold hardy plant that commonly uses as a citrus rootstock. Citrocirus commonly refer to the citranges which are somatic hybrid between the trifoliate and sweet oranges. They are botanically classified as ×Citrocitrus. However a molecular investigation suggested that Fortunella, Citrofortunella, Poncirus and Citrocirus should all be equivocally included in the genus citrus.