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We performed molecular phylogenetic analyses of the Randia clade of the tribe Gardenieae using both plastid and nuclear DNA data. In the phylogenetic hypotheses presented, the African genera Calochone, Euclinia, Macrosphyra, Oligocodon, Pleiocoryne, and Preussiodora are resolved as a monophyletic group. Support is also found for a clade of the Neotropical genera Casasia, Randia, Rosenbergiodendron, Sphinctanthus, and Tocoyena. This Neotropical clade is resolved as sister group to the African clade in analyses of combined plastid and nuclear data. The genus Euclinia appears polyphyletic. The species described from Madagascar represent an independent lineage, the position of which is moreover found to be incongruent between datasets. Plastid and ribosomal DNA data support a sister-group relationship to the mainland African clade, whereas the low-copy nuclear gene Xdh supports a closer relationship to the Neotropical genera. The phylogenetic reconstructions also indicate that Casasia and Randia are not monophyletic as presently circumscribed. A taxonomic proposal is made for the recognition of the Malagasy taxon at generic level as Melanoxerus.

Relationships among 38 taxa of Randia (Rubiaceae, Gardenieae) are estimated using nuclear ribosomal internal transcribed spacers (ITS), the 5S non-transcribed spacer (5S-NTS), and six morphological characters. In addition to Randia, 13 species from eight related genera in Gardenieae (four African, four neotropical) formed the ingroup. Three species from three more distantly related genera in Gardenieae (one African, two neotropical) were chosen as the outgroup. Representatives of the African ingroup genera Calochone, Macrosphyra, Oligocodon and Preussiodora formed a well supported monophyletic group as did the neotropical genera Rosenbergiodendron, Sphinctanthus and Tocoyena. Only when including morphological characters did Randia form a monophyletic group corresponding approximately to contemporary circumscription of the genus, but in this analysis Casasia appears sister to a group of Mexican, Central American, and Antillean Randia. There is no strong jackknife support, however, for either Randia or Casasia to be monophyletic. It is concluded that Randia is comprised of several distinct groups, each with its own geographical distribution. One group of Mexican, Central American, and Antillean Randia, including the type species, can be recognized as Randia in a strict sense. Two other South American groups can be recognized as separate taxa. One of these groups comprises mainly lowland species, and the second is comprised of strictly Andean species.

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