Two new species of Hexasepalum (Rubiaceae: Spermacoceae) from the ʻcampo rupestreʼ of Brazil

The ʻcampo rupestreʼ is a montane vegetation mosaic associated with rocky outcrops, with outstanding levels of species diversity and endemism. Among its most diverse lineages, Rubiaceae ranks among the ten richest families. Hexasepalum Bartl. ex DC. is nested in the Spermacoce clade of Spermacoceae, the largest predominantly herbaceous tribe in the Rubiaceae. The genus comprises 14 accepted species and is distributed mostly in the Americas. Brazil is home to eight species, occurring mainly in the Caatinga and Cerrado (including the ʻcampo rupestreʼ) domains. The analysis of specimens collected in the ʻcampo rupestreʼ of Bahia (NE Brazil) and Minas Gerais (SE Brazil) revealed two species new to science. Hexasepalum bacigalupoae Cabaña Fader & E.L.Cabral sp. nov. and Hexasepalum motaviananum Cabaña Fader, J.A.M.Carmo & R.M.Salas sp. nov. are described and illustrated. We comment on their distribution, habitat, and taxonomy. We also provide an updated key to the species of Hexasepalum in the Americas. Hexasepalum bacigalupoae and H. motaviananum are preliminarily assessed as Endangered and Critically Endangered, respectively, underscoring the crucial importance of conserving the ʻcampo rupestreʼ.