The Paleotropical genus Gaertnera Lam. (nom. cons.) comprises 69 species, plus one presumed natural hybrid, of shrubs and small trees found from West Africa to Sulawesi in southeastern Asia, with 13 of them newly described here. Gaertnera is characterized in the Rubiaceae by its tubular stipules of various forms, secondarily superior ovaries, and drupaceous fruits. Molecular phylogenetic analyses support Gaertnera as monophyletic and sister to the Neotropical genus Pagamea Aubl., but do not support infrageneric classification of Gaertnera. The morphology of Gaertnera is notably variable; molecular analyses indicate that most diversification is within regions, and that much of it is autapomorphic or homoplasious. Gaertnera species of Africa, Madagascar, the Mascarene Islands, and Sri Lanka are hermaphroditic and usually demonstrably distylous, while those of Southeast Asia for which information is available are dioecious, sometimes cryptically so, and apparently derived within the genus. All species recognized here are regional endemics, and accordingly regional keys are included here. In Africa, 12 species and two subspecies are recognized in this present work; G. paniculata Benth. is the most widespread of these; G. aurea Malcomber, G. gabonensis Malcomber, and G. letouzeyi Malcomber are newly described here; and the new combination G. longivaginalis (Schweinf. ex Hiern) E. M. A. Petit var. bracteata (E. M. A. Petit) Malcomber is made based on G. bracteata E. M. A. Petit. In Sri Lanka, six species plus the presumed natural hybrid G. ×gardneri Thwaites are recognized; all of these have been previously described; G. vaginans (DC.) Merr. is the most commonly collected. In Southeast Asia, 14 species are recognized here; G. junghuhniana Miq. is the most commonly collected and widespread; G. alstonii Malcomber, G. aphanodioica Malcomber, G. belumutensis Malcomber, G. capitulata Malcomber, and G. kochummenii Malcomber are newly described here. Gaertnera has its center of diversity in Madagascar and the Mascarene Islands, with 36 species and two subspecies recognized in this present work; G. obovata Baker of Madagascar is the most widespread and common; G. ianthina Malcomber, G. lowryi Malcomber, G. monstruosa Malcomber, G. raphaelii Malcomber, and G. schatzii Malcomber are newly described here; and the new combination G. obovata var. sphaerocarpa (Baker) Malcomber is made based on G. sphaerocarpa Baker. Here, G. vaginans is treated as a morphologically well-defined species of Sri Lanka, and the remaining plants included in this species by some previous authors are treated here in 10 additional species, four of them newly described. The following names are newly lectotypified: G. crinita Drake, G. dinklagei
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