Oxygonum
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Oxygonum comprises about 35 species and is confined to the African continent and Madagascar (Graham 1957; Ortiz & Paiva 1999). Several studies have placed the genus in Polygoneae (Haraldson 1978; Brandbyge 1993; Hong & al. 1998; Galasso & al. 2009), however, Haraldson (1978) suggested a close affinity to Fagopyrum and genera in Rumiceae. Ronse Decraene & Akeroyd (1988) suggested an affinity with Polygonum. Oxygonum has not been sampled in any molecular study, therefore it has been placed as incertae sedis by Sanchez & al. (2011).