Delimitation of genera in the Neotropical tribe Guettardeae (Rubiaceae) has varied; here a key outlines the current taxonomy in South America and southern Central America. Three new species of Chomelia Jacq. are described and illustrated: the unarmed species C. chiquitensis C. M. Taylor of deciduous vegetation in eastern Bolivia differs from C. sericea Müll. Arg. of Bahia, Brazil, in its linear bracts and shorter corollas; the spiny species C. costaricensis C. M. Taylor of humid vegetation in northern Costa Rica differs from C. microloba Donn. Sm. in its longer corolla and lack of domatia on the leaves; and the unarmed species C. torrana C. M. Taylor of wet montane vegetation in northwestern Colombia is distinguished by its short inflorescences with red-violet corollas and its leaves with the higher-order venation not visible. A second species of Neoblakea Standl., N. ecuadorensis C. M. Taylor of seasonal vegetation in western Ecuador, differs from N. venezuelensis Standl. in its leaves broadly obtuse to rounded at the base and its larger fruits. A second species of Pittoniotis Griseb., P. rotata C. M. Taylor, is described based on a specimen from Ecuador and is also known from Peru; it differs from P. trichantha Griseb. of seasonal lowland vegetation in the Caribbean basin in its corollas with shorter tubes, its larger fruits, and its habitat in wet premontane vegetation. The genus Stenostomum C. F. Gaertn. has been recently circumscribed to include several Neotropical species, and three additional species are here transferred to it: Chione darienensis Dwyer, as S. darienense (Dwyer) C. M. Taylor; Guettarda acreana K. Krause, as S. acreanum (K. Krause) C. M. Taylor; and G. turrialbana N. Zamora & Poveda, as S. turrialbanum (N. Zamora & Poveda) C. M. Taylor. Conservation status assessments are presented for all of these species except G. acreanum, which is widespread and in need of further study.