Dismantling the genus Tarenna (Rubiaceae: Pavetteae) in Africa and Madagascar, with the description of three new genera

Abstract As presently circumscribed, the Paleotropical genus Tarenna , belonging to the tribe Pavetteae (Rubiaceae), comprises about 200 species and has its centres of diversity in tropical Asia and Africa. Previous molecular phylogenetic studies of the tribe revealed the polyphyly of Tarenna , suggesting that the genus needs to be recircumscribed. However, a robust phylogeny of Pavetteae using a sufficient sampling of Tarenna and a comparative assessment of the morphological variation of its members throughout the entire geographic range of the genus, needed for such a taxonomic adjustment, are currently lacking. In this study, a new phylogeny of Pavetteae was reconstructed based on four plastid markers ( rps16 , trnT‐F , petD , accD‐psa1 ) and two nuclear markers (nrITS, MADS‐box PI). Our objectives were (1) to produce a robust molecular phylogeny based on a large sampling of Tarenna ; (2) to undertake morphological comparisons between the continental African, Madagascan and Asian/Australasian/Pacific Tarenna ; and, (3) to recircumscribe Tarenna so that the genus is less polyphyletic and to transfer the segregated species to their correct placement within the tribe Pavetteae. Our results support the polyphyly of Tarenna as presently delimited, as its sampled species are resolved in five morphologically distinct and geographically segregated lineages: three restricted to continental Africa, one to Madagascar and the Western Indian Ocean islands and one including the type T. asiatica confined to Asia, Australasia and the Pacific. We propose a narrow circumscription of Tarenna to include the Asian/Australasian/Pacific species but excluding the continental African and Madagascan species. Thirty‐eight continental African Tarenna species are transferred to the hitherto small genus Cladoceras , which is characterized by exotestal cells shaped like puzzle pieces in surface view (versus polygonal exotestal cells in Asian/Australasian/Pacific taxa). The new genus Alatostigma is described to accommodate four continental African species ( A. agnata , A. funebris , A. hutchinsonii , A. jolinonii ) characterized by longitudinally winged abaxial stigma surfaces and polygonal exotestal cells. The new genus Sonbridia , sister to the Paleotropical genus Pavetta , is established to accommodate two continental African species ( S. bipindensis , S. warburgiana , the latter previously known as Tarenna precidantenna ), characterized by short anthers born on long filaments, pedicels thickened below the fruit, and exotestal cells shaped like puzzle pieces in surface view. The species from Madagascar, the Comoros and the Seychelles are transferred to the new genus Nesotarenna , characterized by lax inflorescences, long pedicels, bracteoles borne low on the pedicels and polygonal exotestal cells. The new genera are described in detail and the necessary nomenclatural changes are made to transfer the continental African and Madagascan species to the new genera.