A new species of Paederia L. (Rubiaceae, Rubioideae, Paederieae), P. ntiti Mouly & Puff, endemic to the Comoros (Grande Comore, Anjouan and Mayotte) and occurring in natural elevated forests is described and illustrated. Its conservation status is evaluated and the species is rated ‘Endangered’ (EN). A key to the Paederia taxa of the Comorian archipelago is provided. Also included are notes on the three other species of rubiaceous climbers and lianas known from the Comoros: Paederia bojeriana (A. Rich. ex DC.) Drake, Danais comorensis Drake and Uncaria africana G. Don. In the Comoros, Rubiaceae is one of the largest families of flowering plants, comprising 33 genera and ca 60 species. The family is predominant in several types of primary and secondary vegetation on each of the main Comorian islands. Following a recent survey of the family in the archipelago (Mouly 2009a), two species new to science have been described and a new combination was made within the subfamily Ixoroideae (Mouly and De Block 2008, Mouly 2009b). However, several species belonging to subfamily Rubioideae are still in need of description, amongst them an endemic Paederia L. (Paederieae). This lianescent species is rather rare, and grows in several populations that mostly belong to summit forests in three of the Comorian islands (Anjouan, the Grande Comore and Mayotte). Plants of the Anjouan population were first collected in the late 19th century by Bojer and were then given the provisional name Siphomeris comorensis Bojer, which however, has never been validly published. This nomen nudum and the specimen attached to it (Bojer s.n.) were discussed by Puff (1991b, p. 297). Due to the lack of adequate material, he associated it with another Paederia taxon well known from the Comoros (P. bojeriana (A. Rich. ex DC.) Drake subsp. bojeriana), noting that it is ‘‘a very atypical specimen’’, aberrant in having ‘‘markedly shorter calyx lobes (only ca 1 mm long).’’ Based on recent collections, we are now able to confirm that ‘‘Siphomeris comorensis’’ is a new Paederia species, easily and clearly distinguishable from P. bojeriana. This new species is formally described here, and its position in the genus and its affinities to other species are discussed. Considering the rarity and the declining habitat of the species the conservation status is evaluated. Rubiaceous climbers and lianas are not common in the Comoros (only four species including the one described here). In the light of available treatments for the African mainland and/or Madagascar, and data on species relationships within Rubiaceae, we try to evaluate their affinities. For a generic description of Paederia and the African and Madagascan species, especially P. bojeriana, the reader is referred to Puff (1991a, 1991b). The present taxonomic treatment solely focuses on the species new to science, P. ntiti Mouly & Puff.