(Citrus, Orange, Grapefruit, Lemon, Lime, Citron, Pummelo, Kumquat, Trifoliate Orange)
A genus of about 27-35 species, trees, of s. and se. Asia. Recent studies (followed here) provide compelling arguments in favor of a broad circumscription including Poncirus and Fortunella, based on DNA analyses and other considerations (Bayer et al. 2009; Araújo, Queiroz, & Machado 2003; Mabberley 1997). The recognition of Poncirus and other segregate genera would render Citrus paraphyletic because of the position of Citrus medica (the type species of Citrus) as basal to these genera and the rest of Citrus.
ID notes:Citrus has simple to trifoliolate, evergreen, coriaceous, acuminate, glossy green leaves, and the familiar spherical fruits. Citrus ×limon (Linnaeus) Burman f., Lemon, C. ×paradisi Macfadyen in Hooker (pro sp.), Grapefruit, and C. ×sinensis (Linnaeus) Osbeck, Orange, have been grown on the Outer Banks of North Carolina in Buxton, Dare County, NC (Brown 1959). They are apparently not naturalized there, being killed outright or severely damaged by occasional colder winters, and are not keyed or otherwise treated here.