Citrus taxonomy is complicated and controversial. Different systems place various types of kumquats in different species or unite them into as few as two species. Botanically, many varieties of kumquats are classified as their own species, rather than cultivars. Historically, they were viewed as falling within the genus
Citrus, but the
Swingle system of citrus taxonomy elevated them to their own genus,
Fortunella. Recent phylogenetic analysis suggests they do fall within
Citrus. Swingle divided the kumquats into two subgenera, the
Protocitrus, containing the primitive Hong Kong kumquat, and
Eufortunella, comprising the round, oval kumquat, Meiwa kumquats, to which Tanaka added two others, the Malayan kumquat and the Jiangsu kumquat. Chromosomal analysis suggested that Swingle's
Eufortunella represent a single 'true' species, while Tanaka's additional species were revealed to be likely hybrids of
Fortunella with other
Citrus, so-called x
Citrofortunella. One recent genomic analysis concluded there was only one true species of kumquat, but the analysis did not include the Hong Kong variety, seen as a distinct species in all earlier analyses. A 2020 review concluded that genomic data were insufficient to reach a definitive conclusion on which kumquat cultivars represented distinct species. In 2022, a genome-level analysis of cultivated and wild varieties drew several conclusions. The authors found support for the division of kumquats into subgenera:
Protocitrus, for the wild Hong Kong variety, and
Eufortunella for the cultivated varieties, with a divergence predating the end of the
Quaternary glaciation, perhaps between two ancestral populations isolated south and north, respectively, of the
Nanling mountain range. Within the latter group, the oval, round, and Meiwa kumquat each showed a level of divergence greater than between other recognized citrus species, such as between pomelo and citron, and hence each merits species-level classification. Though Swingle had speculated that the Meiwa kumquat was a hybrid of oval and round kumquats, the genomic analysis suggested instead that the round kumquat was an oval/Meiwa hybrid.
Hybrids Hybrid forms of the kumquat include the following: •
Calamansi:
mandarin orange x kumquat •
Citrangequat:
citrange x kumquat •
Limequat:
key lime x kumquat •
Orangequat:
Satsuma mandarin x kumquat •
Procimequat:
limequat x kumquat •
Sunquat:
Meyer lemon (?) x kumquat •
Yuzuquat:
yuzu x kumquat == Origin and distribution ==