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Citrus taxonomy refers to the botanical classification of the species, varieties, cultivars, and somatic hybrid or graft hybrids within the genus ''Citrus'', subgenus ''Papeda'', and related genera, found in cultivation and in the wild. Citrus taxonomy is very complex. 〔(What is an Orange )〕 Cultivated citrus are derived from various forms of old citrus species found in the wild. Some are only selections of the original wild types, while others are hybrids between two or more ancestors. Citrus plants hybridize easily between species with completely different morphologies, and similar-looking citrus fruits may have quite different ancestries.〔(A genealogy of the citrus family )〕〔 (An Introduction to Citrus )〕〔 Most hybrids express different ancestral traits when planted from seeds (F2 hybrids) and can continue a stable lineage only through vegetative propagation. Others do reproduce true to type via nucellar seeds in a process called apomixis. Many different-looking varieties are nearly genetically identical, and differ only by a bud mutation. Some differ only in disease resistance.〔(【引用サイトリンク】title=The Origin of Cultivated Citrus as Inferred from Internal Transcribed Spacer and Chloroplast DNA Sequence and Amplified Fragment Length Polymorphism Fingerprints )〕 Clear genetic lineages are very important for breeding improved cultivars.〔(【引用サイトリンク】title=Genetic Diversity Assessment of Acid Lime (''Citrus aurantifolia'' Swingle) Landraces in Nepal, Using SSR Markers - Open Access Library )〕 ==Genetic history== Interbreeding seems possible between all citrus plants, and between citrus plants and some plants which may or may not be categorized as citrus. The ability of citrus hybrids to self-pollinate and reproduce sexually also helps create new varieties. The four core ancestral citrus taxa are citron (''C. medica''), pummelo (''C. maxima''), mandarine (''C. reticulata''), and papeda (''C. micrantha'').〔(【引用サイトリンク】title=BMC Genetics - Full text - Next generation haplotyping to decipher nuclear genomic interspecific admixture in Citrus species: analysis of chromosome 2 )〕 These taxa all interbreed freely, despite being quite genetically distinct. They probably arose through allopatric speciation, with citrons evolving in northern Indochina, pummelos in the Malay Archipelago, and mandarines in Vietnam, southern China, and Japan.〔 The hybrids of these four taxa include familiar citrus fruits like oranges, grapefruit, lemons, limes, and some tangerines.〔〔(Phylogenetic Relationships of ''Citrus'' and Its Relatives Based on matK Gene Sequences )〕〔(Citrus limon (L.) Burm. f. (pro. sp.) — Classifications: Lemon ) and more〕 In many cases these crops are propagated asexually, and lose their characteristic traits if bred. However, some of these hybrids have interbred with one another and with the original taxa, making the citrus family tree a complicated network. There are also groups that interbreed with the four core taxa, but which have not historically be categorized as citrus. The trifoliate orange and kumquats do not naturally interbreed with the four undisputed citrus taxa, due to different flowering times,〔(【引用サイトリンク】title=New universal mitochondrial PCR markers reveal new information on maternal citrus phylogeny )〕 but hybrids (such as the citrange and calamondin) exist. Australian limes and ''Clymenia'' are native to Australia and Papua New Guinea, so they did not naturally interbreed with the four core taxa; but they have been crossbred with mandarins and calamondins by modern breeders. Humans have deliberately bred new citrus fruits, by propagating wild-found seedlings (e.g. clementines), creating and/or selecting mutations of hybrids, (e.g. Meyer lemon), and crossing different varieties (e.g. 'Australian Sunrise', a finger lime and calamondin cross). Genetic analysis is starting to make sense of this complex phylogeny. Two citrus fruits have had their full genomes sequenced (sweet orange and clementines). Many different phylogenies for the non-hybrid citrus have been proposed,〔〔(【引用サイトリンク】title=Assessing genetic diversity and population structure in a citrus germplasm collection utilizing simple sequence repeat markers (SSRs) )〕〔 and taxonomic terminology is not yet settled. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Citrus taxonomy」の詳細全文を読む スポンサード リンク
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