mandarin ( C. reticulata ), and grapefruit ( C. paradisi ). These “species” designations are a convenient if inaccurate way to consider this group. Domestication of all but grapefruit occurred before 1000 BCE. The taxonomy of citrus is controversial and reflects a philosophical differences in defining relationships in an ancient group of cultivated plants, complicated by outcrossing, apomixis, and selection (Roose et al. 1995). Thus, Toshio Tanaka proposed 162 species; Walter T. Swingle recognized 16 species, while R.W. Scora, based on biochemical analysis has concluded three primary species: C. medica (citron), C. reticulata (mandarin), and C. grandis (pummelo). Molecular evidence supports the hybrid origin of many so-called species. The Japanese botanist, Tyozaburo Tanaka, has proposed a line of demarcation (now known as the Tanaka Line) from the northeast border of India to the island of Hainan which separates the development of Citrus species and close relatives. The lemon, lime, citron, and pummelo,
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