References

For Exostema

Greuter, W., and R. Rankin-Rodríguez. 2021. Notes on the genus Exostema (Rubiaceae), its limits and sectional subdivision. Taxon Google Scholar

Paudyal, S.K., P.G. Delprete, S. Neupane, and T.L. Motley. 2018. Molecular phylogenetic analysis and generic delimitations in tribe Chiococceae (Cinchonoideae, Rubiaceae). Bot. J. Linn. Soc. 187: 365-396. Google Scholar