# An Overview of Bioactive Flavonoids from _Citrus_ Fruits
## 2 The _Citrus_ Taxonomy  
_Citrus_ is a terrestrial flowering plant that belongs to the family of Rutaceae, the subfamily of Aurantiotiadeae, the tribe of Citreae, and the subtribe of Citrinae (Table 1) [8]. The genus _Citrus_ contains many kinds or types of species that differ regarding their fruits, flowers, leaves, and twigs. The taxonomy of the genus _Citrus_ is complex and controversial, mainly because of sexual compatibility between species and genera, and polyembryony that fixes and reproduces the maternal genotypes. The classification criteria are mainly based on morphological characteristics. There are two principal systems of _Citrus_ taxonomy: [PERSON] [PERSON]'s (1967) system [9], and [PERSON]'s (1977) system [10]. These two authors presented two different concepts of classification. [PERSON] was able to identify only 16 species of _Citrus_, while [PERSON] defined 156 species. The classification of [PERSON] and [PERSON] (1967), based on the edibility of fruits, distinguishes between the subgenus of _Eucitrus_, where all cultivated taxa are grouped, and the subgenus of _Papeda_[9]. The last-mentioned subgenus consists of six species: _C. micrantha_ [PERSON] (currently a synonym of _C. hystrix_ DC. ), _C. ichangensis_ [PERSON] (currently a synonym of _Citrus cavaleriei_ H.Lev. [PERSON] Cavalerie), _C. hystrix_ DC., _C. latips_ (Swingle) [PERSON]. [PERSON], _C. celebica_ [PERSON] (currently a synonym of _Citrus hystrix_ DC.) and _C. macroptera_ Montr. ([PERSON]) (currently a synonym of _Citrus hystrix_ DC. ). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Tribe** & \
\begin{tabular}{c} **Subtribe** \\ **(Subtribe Group)** \\ \end{tabular} & **Genus** &
\begin{tabular}{c} **Number of** \\ **Species** \\ \end{tabular} & **Origin** \\ \hline
2 Tribes & 6 Subtribes & 33 Genera & 203 Species & - \\ \hline \multirow{5}{*}{_Clusenane_} & _Micromelium_ & _Micromelium_ & 9 & S.E. Asia, Oceania \\ \cline{2-5}  & & _Glycosmis_ & 35 & S.E. Asia, Oceania \\ \cline{2-5}  & _Clausenae_ & _Clausen_ & 23 & S. Asia, Oceania \\ \cline{2-5}  & _Murraqu_ & 11 & S. and S.E. Asia, Oceania \\ \cline{2-5}  & _Merillinae_ & _Merillia_ & 1 & S.E. Asia \\ \hline \multirow{5}{*}{_Triphasine_} & _Wenzelia_ & 9 & Oceania \\ \cline{2-5}  & _Monthocitrus_ & 1 & Oceania \\ \cline{2-5}  & _Ovanthera_ & 4 & Oceania \\ \cline{2-5}  & _Merope_ & 1 & S.E. Asia, Oceania \\ \cline{2-5}  & _Triphasine_ & 3 & S.E. Asia, Oceania \\ \cline{2-5}  & _Pamburus_ & 1 & S. and S.E. Asia, Oceania \\ \cline{2-5}  & _Laveugna_ & 12 & S. and S.E. Asia, Oceania \\ \cline{2-5}  & _Paramignya_ & 15 & S. and S.E. Asia, Oceania \\ \cline{2-5}  & _Severinia_ & 6 & S. China, S.E. Asia \\ \cline{2-5}  & _Pleispersimium_ & 5 & S. Asia, Oceania \\ \cline{2-5}  & _Burkillanthus_ & 1 & S.E. Asia, Oceania \\ \cline{2-5}  & _Limnocitrus_ & 1 & S.E. Asia \\ \cline{2-5}  & _Hesprethus_ & 1 & S. and S.E. Asia \\ \cline{2-5}  & _Citropsis_ & 11 & Central Africa \\ \cline{2-5}  & _Atalantia_ & 11 & S. and S.E. Asia \\ \hline \multirow{5}{*}{_Citrinae_ (group B)_} & _Fortunella_ & 4 & S. China \\ \cline{2-5}  & _Eremocitrus_ & 1 & Australia \\ \cline{2-5}  & _Poncirus_ & 1 & Central and N. China \\ \cline{2-5}  & _Clymenia_ & 1 & Oceania \\ \cline{2-5}  & _Microcitrus_ & 6 & Australia \\ \cline{2-5}  & _Citrus_ & 16 & S. and S.E. Asia, S. China \\ \hline \end{tabular}
\end{table} 
Table 1: The subfamily of Aurantioideae [8,11]. The subgenus _Eucitrus_ encompasses ten cultivated species: _C. medica_ L. (citron), _C. aurantium_ L. (sour orange), _C. sinensis_ (L.) Osbeck (sweet orange), _C. limon_ (L.) Osbeck (lemon), _Citrus aurantiifolia_ (Christm.) Swingle (key lime), _C.maxima_ (Burm.) Merr. (pomelo), _C. paradi_si Macfad. (grapefruit), _C. reticulata_ Blanco (mandarin orange), _C. indica_ Yu.Tanaka (Indian wild orange), and _C.tachibana_ (Tachibana orange), which is currently a synonym of _C. reticulata_ Blanco. [PERSON]'s taxonomy is much more detailed than that adopted by [PERSON] and [PERSON].