Citrus taxonomy
All of these hybrids have in turn been bred back with their parent stocks or with other pure or hybrid citrus to form a broad array of fruits. Naming of these is inconsistent, with some bearing a variant of the name of one of the parents or simply another citrus with superficially-similar fruit, a distinct name, or a portmanteau of ancestral species. The Ponderosa lemon ("Citrus limon" × "medica") and Florentine citron ("Citrus x limonimedica") are both true lemon/citron hybrids, the Bergamot orange is a sweet orange/lemon hybrid and the Oroblanco is a grapefruit/pomelo mix, while tangelos are tangerine (mandarin)/pomelo or mandarin/grapefruit hybrids, orangelos result from grapefruit backcrossed with sweet orange, and a sweet orange backcrossed with a tangerine gives the tangor. One lumia, a member of the sweet lemons, is the product of crossing a lemon with a pomelo/citron hybrid, though another lumia variety, the Pomme d'Adam, is a micrantha/citron cross, like the Key lime. The most common and commercially popular 'limes', the Persian limes, are Key lime/lemon hybrids that combine the genetic lineages of four ancestral citrus species: mandarin, pomelo, citron and micrantha.
Watermelon
Citrullus lanatus is a plant species in the family Cucurbitaceae, a vine-like (scrambler and trailer) flowering plant originating in West Africa. It is cultivated for its fruit. The subdivision of this species into two varieties, watermelons ("Citrullus lanatus" (Thunb.) var. "lanatus") and citron melons ("Citrullus lanatus" var. "citroides" (L. H. Bailey) Mansf.), originated with the erroneous synonymization of "Citrullus lanatus" (Thunb.) Matsum. & Nakai and "Citrullus vulgaris" Schrad. by L.H. Bailey in 1930. Molecular data including sequences from the original collection of Thunberg and other relevant type material, show that the sweet watermelon ("Citrullus vulgaris" Schrad.) and the bitter wooly melon "Citrullus lanatus" (Thunb.) Matsum. & Nakai are not closely related to each other. Since 1930, thousands of papers have misapplied the name "Citrullus lanatus" (Thunb.) Matsum. & Nakai for the watermelon, and a proposal to conserve the name with this meaning was accepted by the relevant nomenclatural committee and confirmed at the International Botanical Congress in Shenzhen.